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THERMAL BELTS AND FRUIT GROWING IN NORTH CAROLINA
Harvey J . Cox
THE LIBRARY OF THE UNIVERSITY OF NORTH CAROLINA
THE COLLECTION OF NORTH CAROLINIANA
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W. B. No. 796
U. S. DEPARTMENT OF AGRICULTURE WEATHER BUREAU
MONTHLY
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WEATHER
SUPPLEMENT No. 19
REYIEW
THERMAL BELTS AND FRUIT GROWING IN NORTH CAROLINA
By Heney J. Cox, Meteorologist
APPENDIX:
THERMAL BELTS FROM THE HORTICULTURAL VIEWPOINT
By W. N. Hutt, Former State Horticulturist
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Submitted for publication February 7, 192ff
W. B. No. 796
U. S. DEPARTMENT OF AGRICULTURE
WEATHER BUREAU
MONTHLY
WEATHER
SUPPLEMENT No. 19
REYIEW
THERMAL BELTS AND FRUIT GROWING IN NORTH CAROLINA
By Henry J. Cox, Meteorologist
APPENDIX:
THERMAL BELTS FROM THE HORTICULTURAL VIEWPOINT
By W. N. Hutt, Former State Horticulturist
Submitted for publication February 7, 19
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WASHINGTON
GOVERNMENT PRINTING OFFICE 1923
SUPPLEMENTS T6 THE MONTHLY WEATHER REVIEW.
During the summer of 1913 the issue of the system of publications of the Department of Agriculture was changed and simplified so as to eliminate numerous independent series of Bureau bulletins. In accordance with this plan, among other changes, the series of quarto bulletins — lettered from A to Z — and the octavo bulletins — numbered from 1 to 44 — formerly issued by the U. S. Weather Bureau have come to their close.
Contributions to meteorology such as would have formed bulletins are authorized to appear hereafter as Supple¬ ments of the Monthly Weather Review. (Memorandum from the Office of the Assistant Secretary, May 18, 1914.)
These Supplements comprise those more voluminous studies which appear to form permanent contributions to the science of meteorology and of weather forecasting, as well as important communications relating to the other activities of the U. S. Weather Bureau. They appear at irregular intervals as occasion may demand, and contain approximately 100 pages of text, charts, and other illustrations.
Owing to necessary economies in printing, and for other reasons, the edition of Supplements is much smaller than that of the Monhly Weather Review. Supplements will be sent free of charge to cooperating meteorological services and institutions and to individuals and organizations cooperating with the Bureau in the researches wnich form the subject of the respective supplements. Additional copies of this Supplement may be obtained from the Superintendent of Documents, Washington, D. C., to whom remittances should be made.
The price of this Supplement is 50 cents.
ii
TABLE OF CONTENTS.
Acknowledgments .
Introduction .
Description of region .
General temperature and rainfall conditions in region as
affected by elevation .
Scheme of work and distribution of stations .
Description of topography of the individual slopes and
exposure of the instruments .
Arrangement of tables .
Physical explanation of local variation in temperature in
daytime and nighttime .
Maximum Temperature .
Average monthly and annual maximum temperature .
Average maxima at individual slopes; also maxima during
sunshiny periods .
Variations in maximum temperature in clear and cloudy
weather . .
Rates of decrease in monthly and annual average maximum
temperature on six selected long slopes .
Monthly and annual average maxima at the two stations having, respectively, the highest and lowest elevations. .
Minimum Temperature .
Inversions and norms .
Additional types of inversions .
Mountain breezes .
Average monthly and annual minimum temperature .
Average minimum temperature on individual slopes; also
minima during periods of inversion and norm .
Variation in minimum temperature during periods of
inversion in spring and autumn .
Rates of increase or decrease in average monthly and annual
minimum temperature on six selected long slopes .
Monthly and annual average minima at the two stations having the highest and lowest elevations, respectively. . . .
Norms .
Absolute Maximum and Absolute Minimum Tempera¬ tures .
Range in Temperature .
Absolute range .
Average annual range in temperature .
Daily range and seasonal variation .
Mean Temperature .
Monthly and annual mean temperatures .
Rates of decrease in monthly and annual mean tempera¬ ture on six selected long slopes . .
Monthly and annual mean temperature at the two stations having, respectively, the highest and lowest elevations . .
Page. Pagei
1 Inversions . 55
2 / Topographical and meteorological factors in inversions . 55
2 Selected months of inversions on the long slope at Ellijay
and on the short slope at Highlands . 55
3 Inversions on six selected long slopes having a vertical
4 height of 1,000 feet or more . 58
Inversions on six selected short slopes . 59
5 Inversions of stated amounts on six selected long slopes in
21 the year 1914 . 60
Inversions of stated amounts on six selected short slopes in
21 1 the year 1914 . 63
23 ’•Effects of variation in vapor pressure, relative humidity,
25 j and temperature upon degree of inversion . 64
’Effect of wind direction and velocity upon degree of inver-
26 / sion . 66
* Effect of variation of soil cover upon degree of inversion. . 67
32 Inversions on individual slopes as affected by topography. . 67
Isopleths showing progressive distribution of temperature
33 during a May period of inversion at Ellijay . 75
Mean minimum temperatures during inversion weather at
33, 14 base stations corrected for latitude and to the 2,000-foot
level . 75
34 Approximate vertical temperature gradients during typical
34 periods of inversion . 77
34 Height of Thermal Belt . 78
34 | Average position of the center of thermal belt od nights of
36 ^Seasonal fluctuation of the thermal belt . 79
Top Freezes and Norms . 80
43 Norms on selected long slopes having a vertical height of
1,000 feet or more . 81
44 Isopleths showing progressive distribution of temperature
at Ellijay during a December period . 83
45 \ Hour-Degrees of Frost . 84
45 \ Verdant Zones . 87
Rise in temperature at summit stations earlier than on the
46 valley floor . 89
49 Dew point and ensuing minimum temperature . 90
49 Length of growing season . _ . 92
50 Fruit growing iD the Carolina mountain region and percent-
50 age of crops, 1913-1916 . 95
52 Fruit growing at high elevations in the West . 97
52 Conclusion . 97
53
54
APPENDIX.
Page.
Thermal belts from the horticultural viewpoint . 99
Late blooming varieties . 102
Fruit report for 1914 . 102
Fruit crop report for 1915 . 103
The danger period of 1916 . 104
Page.
Thermal belts from the horticultural viewpoint — Continued.
Frost pockets . 105
Conclusions . 106
Selected bibliography . 106
hi
ILLUSTRATIONS.
Page.
Frontispiece. — Relief map of western North Carolina . opp. 1
Fig. 1. — Average annual rainfall and temperature, western
North Carolina, 1913-1916 . 3
Fig. 2. — Bryson, Contour map and profile . 6
Fig. 3. — Eliijay, contour map and profile . 7
Fig. 4. — Station No. 5, Eliijay . opp. 6
Fig. 5 — Slope north side Eliijay creek facing research stations
showing snow line April 9, 1916 . opp. 7
Fig. 6. — Highlands, contour map and profile . 8
Fig. 7. —Cooperative Weather Bureau staton, Rock House, N.
C. (near Highlands) . opp. 7
Fig. 8. — Station. 3, Highlands, coldest of all stations . opp. 7
Fig. 9. — Blantyre, contour map and profile . 9
Fig. 10. — Station No. 1, Blantyre, on State farm directly below a
northeast slope of French Broad River . opp. 7
Fig. 11. — Station No. 2, Blantyre, on State farm in sag at base
of Little Fodderstack Mountain . opp. 7
Fig. 12. — Stations Nos. 3 and 4, Blantyre, in orchard of State farm
Little Fodderstack Mountain . opp. 7
Fig. 13. — Hendersonville, contour map and profile . 10
Fig. 14. — Station No. 1, Hendersonville . opp. 7
Fig. 15. — Station No. 2, Hendersonville . opp. 7
Fig. 16. — Station No. 3, Hendersonville . opp. 7
Fig. 17. — Asheville, contour map and profile . . . 11
Fig. 18. — North slope in orchard near Asheville, looking down
valley . opp. 7
Fig. 19. — Northerly slope of orchard, in which stations Nos. 2
and 3 are located . opp. 7
Fig. 20. —Southerly slope opposite orchard, Station No. 2a, in
center; Station No. 3a above No. 2a obscured by timber . opp. 7
Fig. 21. — Tryon, contour map and profile . 12
Fig. 22. — Station No. 1, Tryon, on valley floor, Pacolet River — ■
Warrior Mountain in background . opp. 7
Fig. 23. — Warrior Mountain, Tryon, showing location of stations
Nos. 2, 3, and 4 . •. . opp. 7
Fig. 24. —Station No. 3, Tryon, on slope above vineyard . opp. 7
Fig. 25. — Cane River, contour map and profile . 13
Fig. 26. — Altapass, contour map and profile . 14
Fig. 27. — Station No. 2, Altapass, photographed February 28,
1916 . opp. 7
Fig. 28. — Station No. 4, Altapass, orchard on steep slope . opp. 7
Fig 29. — Station No. 5 Altapass, on grass plot on summit, orchard
on left and below . opp. 7
Fig. 30. — Blowing Rock, contour map and profile . 15
Fig. 31. — Grandfather Mountain from Blowing Rock . opp. 7
Fig. 32. — Flat Top Orchard, Blowing Rock, stations 3, 4, and 5. opp. 7 Fig. 33. ■ — Portion Flat Top Orchard from station No. 4, Blowing Rock. Looking southeast small lake in foreground, above
which is station No. 3 . opp. 7
Fig. 34. — South slope of orchard at Valle Crucis, near Blowing
Rock . opp. 7
Fig. 35. — Globe, contour map and profile . 16
Fig. 36. — Gorge, contour map and profile . 17
Fig. 37. — Transon, contour map and profile . 18
Fig. 38. — Wilkesboro, contour map and profile . . 19
Fig. 39. —Mount Airy, contour map and profile . 20
Fig. 40. — Sparger Orchard, Mount Airy, station No. 1 on extreme
left . . . opp. 7
Fig. 41. — Sparger Orchard, Station No. 4, Mount Airy in center, opp. 7 Fig. 42. — Effect of varying inclination and direction of slopes
upon maximum temperatures . 26
Fig. 43. — Thermograph traces, north-and-south-facing slopes, October 30— November 1, 1913, Asheville: Stations 2 and 3, and 2a and 3a are located on opposite slopes facing north and
south, respectively . 27
Fig. 44. Thermograph traces, January 4-5, 1916, Stations Nos. 1,
3, and 4, Cane River . 29
Fig. 45. — Average daily maxima during selected period of clear weather in spring; stations grouped according to elevation above sea level . 33
Page.
Fig. 46. — Average daily maxima during selected period of clear weather in autumn; stations grouped according to elevation
above sea level . . . 33
Fig. 47.— Average daily minima during selected inversion periods in spring: stations grouped according to elevation
above sea level . 35
Fig. 48 — Average daily minima during selected inversion period in autumn; stations grouped according to elevation above sea
level . 35
Fig. 49. — Average daily minima during eight selected norm nights in January, February, and March, 1916; stations grouped
according to elevation above sea level . 46
Fig. 50. — Absolute and average annual maximum and minimum temperatures and range, six long slopes; solid lines show
extremes; shaded, averages . 50
Fig. 51. — Average daily range in temperature, six longslopes _ 51
Fig. 52. — Monthly frequency, average and extreme degrees of
inversion on five selected long slopes . 59
Fig. 53. — Relation of degree of inversion to variation in vapor
pressure and relative humidity . 64
Fig. 54. — Thermograph traces, January 3-5, 1916, stations Nos.
1 and 5, Altapass, showing importation of warm air at summit. . 68
Fig. 55.- — Thermograph traces, May 2-3, 1913, north and south
facing slopes, Asheville . 68
Fig. 56. — Thermograph traces, November 12-14, 1913, stations
Nos. 1, 2, 3 and 4, Blantyre; large inversions. . . 68
Fig. 57. — Thermograph traces, November 1-5, 1916, stations
Nos. 1, 2, 3, and 5, Blowing Rock . 69
Fig. 58.— Thermograph traces, January 27-29, 1914, stations
Nos. 1 and 4, Cane River, large inversion . 70
Fig. 59. — Thermograph traces, December 19-23, 1916, stations
Nos. 1 and 4, Cane River . 71
Fig. 60. — Thermograph traces, November 2-5, 1916, and Novem¬ ber 19-21, 1913, stations Nos. 1, 2, and 4, Hendersonville . 72
Fig. 61. — Thermograph traces, October 11-12, 1916, stations Nos.
2 and 3, Mount Airy; variation in minimum temperature due
to inclination of slope . 73
Fig. 62. — Thermograph traces, October 28-31, 1914, stations Nos.
1, 2, and 4, Tryon . 73
Fig. 63.— Vertical temperature gradients under varying condi¬ tions, October 29-31, 1914, Tryon . 74
Fig. 64. — Isopleths, selected inversion period, May, 1914, Eliijay. 75 Fig. 65. — Approximate free air temperature gradients over western North Carolina during periods of inversion in spring
and fall . 77
Fig. 66. — Average position of thermal belt on six long slopes,
during typical inversion weather . 78
Fig. 67. — Monthly frequency and average and extreme degrees
of norm on six long slopes . 83
Fig. 68. — Isopleths and thermograph traces, selected period
December, 1916, Eliijay . 83
Fig. 69. — Thermograph traces, March 2-4, 1916, stations Nos. 1
and 5, Altapass, and stations Nos. 1 and 5, Eliijay . 84
Fig. 70. — Average number hour-degrees of frost, 10 selected in¬ versions . 86
Fig. 71. — Average number hour-degrees of frost, 10 selected norms 86
Fig. 72. — Average total number hour-degrees of frost, 10 selected •
inversions and 10 selected norms . 87
Fig. 73. — Thermograph traces and vertical temperature grad¬ ients, April 8-10, 1916, stations Nos. 1, 2, and 4, Tryon . 87
Fig. 74. — Possible variation in limits of verdant zone on moun¬ tain slopes . 88
Fig. 75. — Thermograph traces, November 12-13, 1913, stations
Nos. 1 and 5, Gorge . 89
Fig. 76. — Average monthly difference between evening dew¬ point and ensuing minimum temperature . 91
Fig. 77. — Length of growing season . 92
Fig. 78.— Length of growing season ; stations grouped according to elevation above sea level . 93
IV
LIST OF TABLES.
Page.
1. — Monthly and annual average maximum temperatures . 23
la. — Average maximum temperatures during selected clear
periods . . . 24
lb. — Average differences between the maximum temperatures
on the three long slopes of Altapass, Ellijay, and Gorge on selected days of cloudy weather, showing the rate of decrease with elevation . 25
lc. — Rate of decrease in monthly and annual average maximum
temperatures on six selected long slopes . 25
ld. — Monthly and annual average maximum temperatures at
the two stations having the highest and lowest elevation respectively with rates of decrease in elevation . 25
2. — Monthly and annual average minimum temperatures . 35
2a. — Average minimum temperatures during selected inversion
and norm periods . 37
2b. — Rate of increase or decrease in monthly and annual average minimum temperatures on six selected long slopes . 44
2c. — Monthly and annual average minimum temperatures at the two stations having respectively, the highest and lowest elevations with rate of decrease in elevation . 45
3. — Absolute annual maximum and minimum temperatures and
range . 48
4. — Monthly and annual mean temperatures . 52
4a. — Rate of decrease in monthly and annual mean tempera¬ tures on six selected long slopes . 54
4b. — Monthly and annual mean temperatures at the two stations having the highest and lowest elevations with rate of decrease with elevation . 54
5. — Monthly record of minimum temperatures and differences,
May, 1914, Ellijay . 56
6. — Monthly record of minimum temperatures and differences,
May, 1914, Highlands . 57
7. — Monthly record of minimum temperatures and differences,
November, 1914, Ellijay . 57
Page.
8. — Monthly record of minimum temperatures and differences,
November, 1914, Highlands . 57
9. — Monthly record of minimum temperatures and differences,
July, 1916, Ellijay . 57
10. — Monthly record of minimum temperatures and differences,
July, 1915, Ellijay . 58
11. — Monthly record of minimum temperatures and differences,
January, 1916, Ellijay . 58
12. — Monthly record of minimum temperatures and differences,
February, 1915, Ellijay . 58
13. — Total monthly and annual number of inversions of 5° or
more on six long slopes, 1913-1916 . 60
14. — Total monthly and annual number of inversions of 5° or
more on six short slopes, 1913-1916 . 61
15. — Total monthly and annual number of inversions of 5°, 10°,
15°, and 20° on six long slopes, 1914 . 62
16. — Total monthly and annual number of inversions of 5°, 10°,
15°, and 207 on six short slopes . 63
17. — Average hourly temperature during clear humid and clear
dry weather, Ellijay . 65
18. — Effect of wind direction and velocity on inversions . 67
19. — Average minimum temperatures during inversion weather
at 14 base stations, corrected for latitude and to the 2,000-foot level . 76
20. — Seasonal fluctuation of the thermal belt . 80
21. — Monthly record of minimum temperatures March, 1916,
Ellijay . 81
22. — Total monthly and annual number of norms of 5° or more
on six long slopes . 82
23. — Rises in temperature at summit stations . 90
24. — Length of growing season . 94
25. — Length of growing season and number of hour-degrees of
frost combined . 96
APPENDIX.
Page.
1. Summary of horticultural data for season of 1913 . - 100
2. Temperatures at different slope stations, freeze of April
22-23,1913 . . . 100
3. Temperatures at different stations in cold spell of May 11-12,
1913 . 101
Page.
4. Summary of horticultural data for season of 1914 . 103
5. Summary of horticultural data for season of 1915 . 103
6. Minimum temperatures at different stations March 16, 1916. . 104
7. Summary of horticultural data for season of 1916 . 105
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THERMAL BELTS AND FRUIT GROWING IN NORTH CAROLINA
Henry J. Cox, Meteorologist.
ACKNOWLEDGMENTS.
Acknowledgment is made of the assistance of Prof. Charles- F. Marvin, Chief, U. S. Weather Bureau, who in his former position in charge of the Instrument Di¬ vision, cooperated to the fullest extent in supplying in¬ strumental equipment for the observations, and who later advised as to the scope of the research and reviewed the manuscript, offering many helpful suggestions. Ac¬ knowledgment is made to Prof. A. J. Henry, U. S. Weather Bureau, who reviewed and edited the manuscript and gave much time to an examination of the tables, maps, and graphs.
The assistance of those who have taken part in this investigation is also hereby acknowledged: Mr. E. IP. Haines, U. S. Weather Bureau, performed the work in the field and assisted in the compilations and in the preparation and discussion of the material; Mr. W. P. Day, U. S. Weather Bureau, prepared the illustrations and assisted in the compilations and in the preparation and
discussion of the material; Mr. L. A. Denson, U. S. Weather Bureau, made the installations of the stations and gave personal attention to the instrumental equip¬ ment during the period of the research; Mr. W. M. IPutt, formerly State Horticulturist, North Carolina, offered suggestions and advice, with special reference to the horticultural side of the research; Mr. F. R. Baker, Drainage Engineer, North Carolina Department of Agri¬ culture, made surveys of the slopes upon which the ex¬ perimental stations were located and prepared the original topographical maps. Acknowledgment is also made of the courtesies extended by the owners of the various orchards or other properties in which the experimental stations were operated and of the cooperation of the in¬ dividual observers.
A vast amount of tabulated data has been prepared, but the number of tables published has necessarily been greatly reduced for want of space.
1
INTRODUCTION.
A research (upon the thermal conditions in the North Carolina mountain region) was inaugurated in 1912 by the United States Weather Bureau at the request of the North Carolina State Board of Agriculture and the State Horticulturist, with a hope that the so-called Thermal Belts might be more clearly defined, and that safe eleva¬ tions in the various sections for the planting of fruit trees might be determined, as far as possible.
Considerable success had been obtained in many por¬ tions of that region in the growing of hardy fruit, es¬ pecially apples, but here and there marked failures had occurred, supposedly because either of too great altitude or of unfavorable topography, inducing freezes in the one case and severe frosts m the other.
Heretofore the planting of orchards in the mountain region had been carried on in a rather haphazard way, so far as the influence of temperature conditions was con¬ cerned, and it was believed by the State Horticulturist that an exhaustive study of the various problems might furnish valuable information for the guidance of or- chardists in the development of their properties.
The special meteorological stations that were estab¬ lished in the North Carolina mountain region for the purpose of this study at points shown in relief map in frontispiece were conducted under the direction of the Weather Bureau,' while the State Horticulturist has afforded assistance with advice and suggestions.
Reference has frequently been made in meteorological and climatological literature to thermal belts or frostless zones in mountain districts, both in this country and in Europe. These belts, of varying width in which frost is never observed, were said to be found on certain slopes between the valley floor and the summit, their development being mainly due to the fact that during certain cool nights the temperature is relatively high on the slope — much higher than at the base.
This phenomenon, termed the inversion of temperature, is observed most frequently on clear, quiet nights, but somefctimes on partly cloudy and even cloudy nights. It is called an "in version” because ordinarily we expect a fall in temperature with elevation, which, for the want of a better name, we may here term a “norm” in contrast with the term “inversion. ” On the average the tempera¬ ture of the free air falls with height, the mean rate of decrease being 1° F. in 300 feet of ascent, and there are many nights in the mountain region when this decrease in temperature with elevation or even a greater one is observed, especially when the weather is cloudy and windy. There are still other nights, moist and damp, when the differences in temperature between various ele¬ vations are hardly appreciable.
Both inversions and norms prevail within mountain valleys to a considerable vertical height, and are important factors in the question of fruit growing. In the one case the minumum temperature is lowest at the base and high¬ est at some point on the slope or at the summit, while in the other case the minimum is lowest at the summit and highest at the base; and, through a combination of these two conditions, we sometimes have a belt more or less indefinite in width where the minima average higher than 2
at either the base or the summit, free from the frosts of the valley and from the freezes of the higher levels. Within this belt, which might properly be called a “verdant zone,” the foliage is fresh and green as compared with that above and below.
DESCRIPTION OF REGION.
More has probably been written regarding thermal belts in the North Carolina mountains than in any other section of the country, doubtless because the phenomena are more pronounced there than elsewhere in the East on account of the more extensive slopes and the greater area. The Appalachian Mountains, which form the divide be¬ tween the great central valleys of theUnited States and the Atlantic Plain, extend in a southwest-northeast direction from Pennsylvania to northwest Georgia, but the cul¬ minating section of the system lies in western North Carolina. While the elevation of the Atlantic Plain at the base of the mountains is only 150 feet in Pennsylvania, and perhaps 500 feet in Virginia, in North Carolina it rises to about 1,000 feet.
The Appalachians divide into two chains in Virginia, one known as the Great Smokies, continuing in its south¬ westerly course and forming the boundary of western North Carolina, and the other, retaining the name of the Blue Ridge, as the range in the north is called, crossing the State farther eastward and forming the great watershed of the drainage of that section. Be¬ tween the two chains lies a remarkable region of valleys and plateaus, at no point falling to a lower elevation than 2,000 feet, while portions of the plateau in Watauga County to the north and Macon County to the south have elevations ranging from 3,500 to 4,000 feet. Within this system scores of mountain peaks rise to an altitude of more than 5,000 feet, and many even more than 6,000 feet, Mount Mitchell being the highest, with an elevation of 6,711 feet.
The North Carolina mountain region, then, is preemi¬ nently a land of high mountains and plateaus, and because of its elevation it is known as the “Land of the Sky,” a region most irregular in shape, having an area of over 5,000 square miles and extending in a northeast-south¬ west direction, about 125 miles.
In a general view the eastern chain, or Blue Ridge, is seen to be irregular and fragmentary, while the western chain, the Great Smokies, is more regular, elevated, and continuous. Nevertheless, the drainage of the plateau between the two is thrown entirely to the westward. Numerous cross chains uniting the main ranges form basins which contain the mountain tributaries of the Tennessee River. Projecting into the Piedmont region east of the Blue Ridge are a few detached chains and isolated knobs.
The principal streams of the mountain region rise in the Blue Ridge, and those trending westward break through the more elevated western barrier in deep chasms, the French Broad, the North Toe, and the Pigeon, all three flowing into the Tennessee; and the Tuckasegee, into the Little Tennessee; while those on the other side of the
THERMAL BELTS AND FRUIT GROWING IN NORTH CAROLINA.
ridge trending eastward are the Yadkin, emptying into Ree Pee River? and the Catawaba, separated from the i adkin by the Brushy Mountains and flowing first easterly and then southerly through the Piedmont region into the Atlantic.
. The mountains are for the most part covered with timber up to their very summits, even Mount Mitchell having considerable forest growth at the highest points; but there are a few peaks, termed “ Balds, with eleva¬ tions of 5,000 feet or more, whose rounded knobs are almost bare of timber.
The relief map in the frontispiece shows the general topography of the region.
GENERAL TEMPERATURE AND RAINFALL CONDITIONS IN REGION AS AFFECTED BY ELEVATION.
The modifying effect of elevation on the general meteorological conditions of the region is twofold — viz, a reduction in temperature and an increase in rainfall. The isotherms as they approach from the eastern low¬ lands curve southward rapidly and, after crossing the mountains more or less irregularly at right angles, bend sharply northward, while the rainfall is much greater in the mountain region than at the lower levels, and is greatest over the more elevated sections, especially those on the side of the mountains facing the rain¬ bearing winds.
Figure 1 gives the average annual percipitation over western North Carolina for the four years 1913^1916. Isotherms for the same period are also shown and in the upper left-hand corner will be found a key to the loca¬ tion of the observing stations, also the mean annual
temperature and elevation above mean sea level of the base stations.
Taking temperature conditions in the sections to the east of the mountains as a basis, there is normally, because of the difference in latitude, about 2° difference in the mean annual temperature between the northern and southern limits of this mountain region. In the lower levels the isotherm of 59° F 1 runs somewhat south of the Virginia-North Carolina border, while that of 61° is approximately in line with the Georgia-North Carolina boundary. Temperature data for the summits of the highest mountains in North Carolina are not available, but the means deduced from the observations at places
having altitudes up to 4,000 feet are sufficient to show strikingly the effect of elevation upon temperature. The lowest annual mean for a considerable period in the mountain region is 49° at Blowing Rock and Highlands, both about 3,600 feet above sea level, the first in the extreme northwestern portion and the other in the extreme southwestern portion of the State. Because of the difference in latitude, Blowing Rock should nor¬ mally average 2° colder than Highlands, but this varia¬ tion is not apparent in the observations because of the difference in topography, the station at the latter place being located in a well-marked frost pocket where the night temperature averages uniformly low. This mean annual temperature of 49° is approximately the mean of .the Weather Bureau station at Albany, N. Y., where the thermometer shelter stands about 100 feet above sea level.
1 Fahrenheit degrees and English units are used throughout this discussion.
Meon Annuo! Temperature
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GORGE © GLOBE ® BRYSON © BLANTYRE © /-iENDERSONY/LLB @ ALTARASS* t @ ELUJA Y 0 ASH3Y/LL3.
Fig. 1.— Average annual rainfall and temperature, western North Carolina, 1913-16.
4
SUPPLEMENT NO. 19.
The rainfall in the Carolina mountain region, as shown in Figure 1, varies considerably and it is generally much heavier than on the Atlantic Plain. The largest amounts occur along the main Blue Ridge, especially on its south¬ ern and eastern sides, as the principal rain-bearing winds in that section are from east to south. The southerly winds carry the moisture-laden air from the Atlantic and the Gulf of Mexico, and naturally the greatest rainfall is recorded at the stations farthest to the south, where these east to south winds, moving inland, pass upward over the slopes, the cooling of the air resulting in con¬ densation, often excessive. During a four-year period, 1913-1916, inclusive, the gauge at Highlands registered an average annual precipitation of 97.86 inches, the total in 1915 being 111.21 inches, and in 1916, 105.10 inches, two extremely wet years. In the same period the cooper¬ ative station at Rock House, formerly known as Horse Cove, (Fig. 7), about six miles southeast of Highlands, recorded an average rainfall of 94.62 inches. These figures are considerably above the average for a long eriod of years, which are, respectively, 80 and 82 inches, ut in any case this spot in the mountain region close to the North Carolina-Georgia boundary is the wettest place in the United States except the extreme northwest racific coast.
The rainfall over the Great Smokies is much less than along the Blue Ridge, because the southerly and easterly rain-bearing winds are shut off, or at least their moisture is largely condensed over the Blue Ridge before reaching the Smokies. Moreover, the rainfall on the plateau in¬ closed by these two mountain ranges is very much less than on the surrounding mountains, obviously because of the condensation of alarge portion of the moisture at the higher levels before the winds reach the plateau. Asheville, in the valley of the French Broad River and walled in by mountains has an average annual rainfall of only 39 inches.
SCHEME OF WORK AND DISTRIBUTION OF STATIONS.
Although the special research was inaugurated in 1912, it was not until the first part of 1913 that all the stations selected were in full operation. Stations were installed at 16 places in the mountain region, Bryson, Ellijay, Highlands, Waynesville, Blantyre, Hendersonville, Ashe¬ ville, Tryon, Cane River, Altapass, Blowing Rock, Globe, Gorge, Transon, Wilkesboro, and Mount Airy. Bryson is the most westerly, Mount Airy, close to the Virginia border, the most northerly and easterly, and Highlands and Tryon, close to the Georgia and South Carolina borders, respectively, the most southerly. At the 16 points of of observation there was a total of 68 stations, varying at each point from 3 to 5. The point having the greatest elevation is Highlands, where the stations range from 3,350 feet to 4,075 feet in altitude, and the lowest is Tryon, its base station having an altitude of only 950 feet. Six of the slopes, Ellijay, Tryon, Cane River, Altapass, Globe, and Gorge, have differences in elevation between base and summit of 1,000 feet or more, the longest slope, 1,760 feet, being at Ellijay. Some of the slopes are steep, and others are gentle, irregular, and broken up into coves and frost pockets. Some are heavily timbered, while others are comparatively free from forest growth, just as certain of the individual stations are surrounded by dense vegetation while others are more or less bare.
At one point, Asheville, the stations were located above a valley floor on two slopes, northerly and southerly, facing each other, while at two other places, Bryson and Mount Airy, the stations were on slopes leading down
from different sides of knobs. Nearly all the short slopes lead up to isolated knobs, also some of the longer ones, and in other cases there is a large extent of surface area near the summit. Some of the valleys at the base of the slopes are narrow and confined, and others are com¬ paratively broad ; again, some base stations are located on broad benches. A wide range of conditions has thus been afforded for investigation.
The places were fairly well distributed geographically, all being located in the main portion of the mountain district with the exception of Wilkesboro and Mount Airy, which lie in the foothills to the east. Two places, Blowing Rock and Altapass, are on the main Blue Ridge. There was no definite uniformity observed in determining the positions of the stations on the individual slopes, the exact locations in some cases being dependent upon conditions beyond the control of the leader, the purpose being to place at least one or two stations in each group within an orchard, when one was available.
The task of selecting locations for the stations was rather difficult. The purpose was, of course, to make as complete a survey as possible of the meteorological con¬ ditions in the mountain region. The scope of the work, however, had its limitations because of the difficulty in securing and training competent observers and because of the impracticability of locating stations in some cases where most desired. To do the observation work with absolute completeness, experienced observers should have been located at many elevated points well-nigh inac¬ cessible; but this was, of course, impracticable. The bureau was obliged to select places where men were available to take observations, generally superintendents or foremen employed in the orchards, and these men had to be trained as observers, the observation work being incidental and in addition to their regular duties.
The places selected were for the most part on slopes having orchards already planted, the number of stations at each place averaging four. For purposes of conven¬ ience the stations were numbered in consecutive order from the base to the summit, station No. 1 being on the valley floor, or at least at the base of the particular slope, and stations Nos. 3, 4, or 5, as the case might be, at the summit, or as far up as practicable. In some places, where there was a further descent below the base, as at Altapass, the No. 1 station was not placed actually on the valley floor; while at a few places, as at Asheville, the highest station was not at the summit, the location in each case being governed by the exigency of the situation.
The observations continued at all 16 places until the close of 1916, with the exception of Waynesville, where the work was terminated in the middle of the period. The data at that place, on account of this interruption, have consequently not been included herein. For the sake of uniformity and convenience, the dicussion of the observations in this research is limited to the four years, 1913-1916.
The individual stations were furnished with ther¬ mometer shelters containing thermographs and maxi¬ mum and minimum thermometers, these instruments being placed about 5J feet above the ground; and one station in each place, called the “home station,” was supplied with a mimimum thermometer attached to the outside of the shelter, a sling psychrometer, and a rain gauge. This home station was the one nearest to the residence of the observer — at some places at the base, at others on the slope or even on the summit, depending upon the convenience of the particular point to the observer’s residence. At the home stations the observa-
THERMAL BELTS AND FRUIT GROWING IN NORTH CAROLINA.
5
tions were made and the thermometers set daily, while at the other stations the readings were made twice a week only, the thermograph traces, however, furnishing a continuous record. However, the data at the home stations are more complete and dependable than at the others. In addition to the instrumental record of temper¬ ature and precipitation, data as to wind direction and estimated velocity, especially at sunrise and sunset, and notes as to the character of the weather during both day and night were kept by the observers. The regular equip¬ ment at Tyron was supplemented by a hygrograph at station No. 3.
There were not available at any of the special stations instrumental records of wind or sunshine, but the records of the regular Weather Bureau station in the city of Asheville have been used to supplement the observations made in the field. Asheville is fortunately located in the very center of the region under investigation, and one group of orchard experimental stations was estab¬ lished a few miles distant from the city.
Moreover, the observations made by the orchard ob¬ servers were supplemented in the spring of 1916 by special work at Ellijay, Highlands, Tryon, and Blowing Rock by Mr. E. H. Haines, of the Chicago Weather Of¬ fice, and in the spring of 1915, at Ellijay and Highlands by Prof. H. H. Kimball and Mr. R. N. Covert, of the Central Office at Washington. Professor Kimball’s ob¬ servations2 have already been published.
TOPOGRAPHY OF THE INDIVIDUAL SLOPES AND THE EXPOSURE OF THE INSTRUMENTS.
A complete description of the conditions under which the instruments were exposed is essential to an under-
* Kimball, H. H., Nocturnal Radiation Measurement?, Monthly Weather Review, February, 1918, 46 : 57-60.
standing of the observations, and detailed statements regarding the environment of each group of stations will be found with the contour maps of the respective stations. It is important to know whether the slope is steep or gentle, whether regular or broken up into coves and pockets; also its height above the base and above sea level, the direction of its inclination, its general environ¬ ment as regards topography and vegetation — in a word, to know every condition that might possibly affect the temperature, rainfall, humidity, or wind. It will be found later, as the observations are discussed, that exposure and environment have a most important bear¬ ing upon the situation.
The stations are not located necessarily at the exact oints where the numbers appear in the relief map, ecause these numbers are entered at the positions of the various cities or villages, while in many instances the experimental stations are a few miles distant. This variation will be explained under the description of each group of stations, and the special contour maps and accompanying profiles will show in detail the local topog¬ raphy at each place. The profiles indicate the vertical distances between the base and the summit stations and the vertical and horizontal distances from station to station. As stated previously, the lowest, or base sta¬ tion, is always numbered 1, while the highest in the group has been numbered 3, 4, or 5, as the case may be, depending upon the number of stations employed.
u the descriptions of the stations and their exposures, only important features are mentioned; but these, at least, are necessary to an understanding of the observa¬ tions.
The shaded portions of the topographical maps indicate cleared areas in the vicinity of the observation stations.
The arrangement of the stations is from west to east, following the numbers on the relief map which forms the frontispiece.
SUPPLEMENT NO. 19.
BRYSON.
Capt A. M. Frye, Observer.— A group of four stations in the orchard of the observer, about 2 miles northeast of the village of Bryson and U miles (north of the Tuckasegee River, on the valley floor of Deep Creek in a region hemmed in on the north by the spurs and ridges of the
rated from station No. 1 by a knob, the summit of which is about 400 feet southwest of station No. 2. No. 2a, home station, on south slope 385 feet above station No. 1; same elevation as station No. 2, but over the hill and on the opposite side; shelter in midst of orchard close to apple trees; ascending slope on all sides, except gradually descending on south side between two hills; timber to south and west about 100 feet
Fig.
2. — Bryson, contour map and profile.
Great Smokies and on the south by the Yalaka Mountains; mountains at varying distances tower above on nearly all sides. Base station, No. 1, 1,800 feet above sea level, in a grass plot on a flat plain with the country in the immediate vicinity rolling and broken. Station No. 2, in a cove or gully 385 feet above and in a horizontal direction 3,000 feet northeast of station No. 1; in the midst of apple orchard, the trees being a few feet from the shelter on all sides; on northerly slope sepa-
distant. Station No. 3 on a small knob 5?0 feet above station No. 1; not in orchard; shelter surrounded by ferns and scrub oaks; also high timber to the south and southwest 15 to 20 feet and to the east 30 feet distant; sharp descent to orchard below. The slope in the orchard, as a rule, is quite gradual. The vertical distance between stations Nos. 1 and 3 is 570 feet, and the horizontal distance is 3,000 feet, a grade of 12°.
M. W. R., Supplement No. 19.
(To face p. 6.)
Fig. 7. — Cooperative Weather Bureau station, Rock House, N. C. (near Highlands).
Fig. 8.— Station No. 3, Highlands— coldest of all stations.
M. W R., Supplement No. 19.
(To face p. 7.)
Fig. 10. — Station No. 1, Blantyre, on State farm directly below a northeast slope of French Broad River.
Fig. 11— Station No_ 2, Blantyre, on State farm in sag at base of Little.Fodderstack Mountain
Fig. 12. Stations Nos. 3 and 4, Blantyre, in orchard of State farm on Little Fodderstack Mountain,
M. W. R., Supplement No. 19.
(To face p. 7.)
Fig 14. — Station No. 1, Hendersonville.
Fig. 15.— Station No. 2, Hendersonville.
Fig. 16. — Station No. 3, Hendersonville.
Fig. 18. — North slope in orchard near Asheville, looking down valley.
Fig - 19. — Northerly slope of orchard in which stations Nos. 2 and 3 are located
Fig. 20.— Southerly slope opposite orchard, station No. 2a in center; station No. 3a above No. 2a obscured by timber
M. W. R., Supplement No. 19.
(To face p. 7.)
Fig. 22.— Station No. 1, Tryon. on valley floor Pacelet River, Warrior Mountain in background
Fig. 2.3 —Warrior Mountain, Tryon, show ing location of stations Nos. 2, 3, and 4.
Fig. 28. — Station No. 4, Altapass; orchard on steep slope.
Fig. 29. — Station No. 5, Altapass, on grass plot on summit, orchard on left and below
M. W. R., Supplement No. 19
(To face p. 7.)
Fig. 31. — Grandfather Mountain from Blowing Rock.
Flo. 32.— Flat Top orchard, Blowing Rock, stations 3, t. and ■'>.
Flo. 40. Sparger orchard. Mount Airy, station No. 1 on extreme left.
Fig. 41. -parser orchard, station No. 4. Mount Alrv, In center
THERMAL BELTS AND FRUIT GROWING IN NORTH CAROLINA.
ELLIJAY.
thfir MinCV' °}>sen)er—^? Elliiay stations, on the property of on a steep northerly slope of a spur of the Cowee Moun¬ tains, the base station, No. 1, being in the valley floor of Ellijay Creek at an elevation of 2,240 feet, while the high station, No. 5, is on the summit of a knob 1,760 'feet above the base and 4,000 feet above sea level . k ation -No. 1, in a field about 30 feet south of the creek, over grass plot, at a considerable distance from any trees; across creek to the north,
station No. 1, over sod in apple orchard on moderate slope though steeper above and below, slope broken up into ridges and hogbacks. Station No. 4, 1,240 feet above station No. 1, in clearing and on edge of steep northerly slope, in corn and potato patch; brush about 16 feet to the west; some timber 100 feet to the west and southwest. In winter sun shut off during greater part of day. Station No. 5, 1,760 feet above station No. 1, a level field near the summit of a high knob, another prominence, Peak Knob, 180 feet higher than station No. 5, distant 1,800 feet to the south; timber to the west, southwest and south, mostly
steep high slopes, more or less broken, while to the south, slope abrupt near the valley floor; orchard at some distance south of shelter on north¬ erly slope broken and uneven with natural terraces here and there; valley narrow and trending in east-west direction, almost entirely inclosed by mountains. Station No. 2, in orchard, on rather steep northerly slope with ferns and weeds on all sides, 310 feet above station No. 1; timber to north, northwest, west and southwest; cleared land directly to east, northeast, and southeast, and for some distance to the south, about 500 feet. Station No. 3, the home station, 620 feet above
dead, close by; abrupt slopes to the north and east. (See fig. 4, Peak Knob in the distance to the right.) Ellijay Creek, near which station No. 1 stands, flows in a westerly direction through a narrow valley, and the slope on the north side is broken up into spurs and hogbacks. (See fig. 5 for photograph taken from station No. 4, showing mountains and slopes on north side of Ellijay Creek.) For a vertical distance of 1,760 feet between stations Nos. 1 and 5 at Ellijay, there is a hori¬ zontal distance of about 5,100 feet, equivalent to an average grade of 19°. The grade on some portions of the slope is more than 30°.
8
SUPPLEMENT NO. 19.
HIGHLANDS.
T. G. Earbison, Observer. — Highlands is on an elevated plateau close to the Georgia border, and its group of five stations is on the property of the observer in two different orchards more than 2 miles apart, No. 1 and 2 being in the Satulah orchard on a southerly slope directly below Mount Satulah, and Nos. 3, 4, and 5 in the Waldheim orchard on the southeast slope of Dog Mountain. These stations have the highest elevation of all used in the research, station No. 5, near the summit of the Waldheim orchard slope, having an altitude of 4,075 feet. The place is near the southern end of the Blue Ridge. There are several mountain peaks in the vicinity, the more prominent being Satulah and Whiteside, with elevations of 4,560 and 4,930 feet,
feet distant. Timber within 30 or 40 feet of shelter and between it and Mount Satulah, located to the northeast and north, which towers directly above and appears like an immense rock reaching an elevation of more than 1,000 feet above station No. 2. The grade from that station to the summit of the rock is 45°, while the average grade in the orchard itself is only 10° or 11°; timber to west is close by and reaches also a little to the south and is rather high. Station No. 3, the base station of the group in the Waldheim orchard, has an elevation of 3,675 feet above sea level; shelter in grass plot in a sink immediately below orchard; slope above not steep, except near the lower edge directly above station No. 3, and for a short distance above station No. 4. Station No. 3 near the bottom of a general east to southeast slope, surrounded by trees, except where the ground slopes upward
Fig. 6. — Highlands, contour map and profile.
respectively. Highlands is only a few miles northwest of Rock House or Horse Cove, where the largest amount of rainfall in the United States is recorded with the exception of the extreme north Pacific coast. (Fig. 7 shows the cooperative station at Rock House, the thermometer shelter being in the center of the picture.) Station JNo. 1, in the Satulah orchard, the home station, 3,350 feet above sea level, almost directly south of Mount Satulah and about 1,500 feet distant from its base. The ground slopes rapidly away from the shelter to the southeast and west. Slope rather moderate immediately to the north in orchard ; in fact, slope in that direction does not become steep for more than 1,000 feet, but beyond that point toward Mount Satulah the grade is quite steep. Station No. 2, 200 feet above station No. 1, in a horizontal direction about 1,000 feet distant. Shelter located over a grassy plot with apple trees all around and only a few
toward the orchard on the northwest side; no descent on any side of this depression, but land somewhat broken. The depression is a natural frost pocket. (Fig. 8 shows station No. 3, looking to the northwest toward orchard.) Station No. 4, 200 feet above station No. 3, on a southeast slope in orchard over sod covered with grass, weeds, and bushes in the midst of apple trees; slope at this point moderately steep and in an east-southeast direction. Station No. 5, 400 feet above station No. 3, in apple orchard 20 to 30 feet below upper limit; slope moderate near shelter and moderately steep most of the way down; shelter 150 to 120 feet below the summit of Dog Mountain. Timber above orchard to the west and northwest, also to the south, but not heavy, the closest timber being about 25 feet distant. Average grade between stations Nos. 3 and 5 is 16°, much greater than between stations Nos. 1 and 2 in the Satulah orchard.
THERMAL BELTS AND FRUIT GROWING IN NORTH CAROLINA.
BLANTYRE.
John E Davidson Observer. -A group of four stations on the State h arm at Blantyre, located in the vallev of the French Broad River which is rather wide at this point. The river falls here at the rate ?, only about 100 feet in 35 miles of meandering over the plateau. Base station No. 1, close to the valley floor, 2,090 feet above sea level; the other three stations about a half-mile distant on the northwest slope of Little Fodderstack and separated from the base station by a gradual ascent partly timbered. Big Fodderstack, a few hundred
southeast and a small hill to the north and northwest; shelter in lower edge of apple orchard. Above station No. 2 the grade rather steep and the side of the mountain terraced; the slope broken up consider- ably in various directions. The sag in which station No. 2 is located slopes gently from the southwest to the northeast; and this is apart from the general slope thence upward to summit of Little Fodderstack in a southeast to south direction. Station No. 3 in the midst of apple orchard, 150 feet above station No. 2, is about half way up Little Fodderstack. Shelter located on a hogback or ridge 50 or 60 feet broad running northwest down to station No. 2. Slope down, steep,
Fig. 9. — Blantyre, contour map and profile.
feet higher than Little Fodderstack, distant about a mile to the south¬ west, but no high mountains in the immediate vicinity. Nine or ten miles away are several high peaks, including Mount Pisgah, which stands to the northwest in the distance with a maximum height of 5,749 feet. Country in immediate vicinity of research stations rolling and broken. Station No. 1, home station (fig. 10), over a grass plot slightly above the bottom lands on one of several terraces 15 feet wide, with moderate slope; gentle slope upward in rear of shelter to the south and southwest only few degrees to base of Little Fodderstack; to the southeast of shelter a peach orchard in terraces about 30 feet distant from shelter. Station No. 2 (fig. 11), 300 feet higher than station No. 1, in a sag between Little Fodderstack to the
20 feet northwest of shelter, slope upward directly beyond shelter, more moderate. Station No. 4, 300 feet above station No. 2 and 600 feet above station No. 1; shelter on a hogback almost on summit of Little Fodderstack, but the ground a few feet higher to the south, southeast, and east; 20 to 40 feet south and southeast of shelter it slopes almost generally in all directions. Sparse timber southwest, south, southeast, and east of shelter 20 to 40 feet distant; clear view at station No. 4 at sunrise and sunset; shelter located overgrass and just beyond upper limit of orchard. Average grade between stations Nos. 2 and 4 about 22°, only a few slopes, such as Altapass, Ellijay, Globe, and the China orchard at Blowing Rock having sections any steeper. Fig. 12 gives good view of orchard including stations Nos. 3 and 4.
10
SUPPLEMENT NO. 19.
HENDERSONVILLE.
S. McCarson, Observer.— The group of four stations at Hendersonville located 3 miles to west of the city, the base station in a meadow and the other three in the apple orchard of Capt. M. 0. Toms on the moderate slope of Echo Mountain, or Hickory Hill, some distance southwest of the base station. This group of stations is only about 7 miles distant from Blantyre on the other side of the French Broad River. Jump Off Mountain, the most prominent point in the vicinity, with an elevation of 3,141 feet, lies distant less than a mile west of Echo Mountain, which
respectively; brush and scrub pine to west 40 feet and timber to west about 300 feet distant. Station No. 2 (fig. 15) over thin grass on sandy soil 450 feet above station No. 1, and 3,500 feet distant in a horizontal direction west by south, at the bottom of apple orchard; timber, not heavy, surrounds shelter from southwest to northeast by way of south¬ east, at varying distances, forming a semicircle. Station No. 3 (fig. 16) in midst of apple orchard, soil covered with grass, 600 feet above station No. 1, on a uniform northeast to east slope from the summit; slope at No. 3 more easterly, continuing in that direction for descent of from 40 to 50 feet, then a little gap between two small knolls to the
Fig. 13.— Hendersonville, contour map and profile.
has an elevation of 2,950 feet, there being a sag between the two knobs. There is also a small knob, Mount Davis, a short distance to the north and of about the same elevation as Echo Mountain. Below these mountains there is a more or less gradual downward slope in practically all directions to an extensive plain which reaches for many miles, mountains in the distance surrounding. Station No. 1 (fig. 14), 2,200 feet above sea level on a bench some distance removed from the valley floor, on a grassy plot with a very slight declination to the east; shelter surrounded by timber except at opening to east through a narrow gap; slight slopes upward to north and south, on both of which timber is located, the timber being 30 to 50 feet north and south of shelter,
north and to the south. Station No. 4, the home station, 750 feet above station No. 1, in apple orchard on the knoll called Hickory Hill or Echo Mountain. The shelter distant 10 feet or more from small apple trees, with clover, grass, and weeds covering the soil. The general slope at Hendersonville is more gradual than at any of the other places, except possibly Gorge and Transon, the slope being sharp at only a few points. The average grade between stations Nos. 1 and 4 is only 7° and that between stations Nos. 1 and 2 about the same. However, the grade between station Nos. 3 and 4 is somewhat steeper. There is here a wider expanse of surrounding plains than in the vicinity of any other station, except possibly Wilkesboro and Mount Airy.
THERMAL BELTS AND FRUIT GROWING IN NORTH CAROLINA.
ASHEVILLE.
Chas. I . Joyner , Observer. — The five stations on Mr. Chas. H Webb’s P^Pert+y> abo,l.lt 4 mile8 northeast, of the city of Asheville, on a bench bove the valley of the French Broad River, which is approximately the center of the North Carolina mountain region. Mr. Webb’s prop¬ erty lies on the north and south slopes of Bull Cove Branch (fig. 18 photograph taken from north slope in the orchard looking dow^i the
of the top of a spur reaching westward from the peak of Bull Mountain, which towers a thousand feet above, but station No. 3a, in a clearing surrounded by timber on the opposite slope, is within about 100 feet of the summit of the ridge, projecting across from Rice Knob. The southerly slope is much steeper than the northerly one. While stations Nos. 3 and 3a are each 380 feet above station No. 1, the horizontal distance on the south slope is only 1,200 feet, while it is 2,000 feet on the north slope. The north slope is broken up into ridges and hog-
valley toward the city of Asheville). Station No. 1, the home station, over grass at an elevation of 2,445 feet above sea level, in a sag between northerly and southerly slopes. Stations Nos. 2 and 3 on rough broken soil in apple orchard (fig. 19) on a northerly slope of Bull Mountain, 155 feet and 380 feet, respectively, above station No. 1. Stations Nos. 2a and 3a on the opposite southerly slope (fig. 20) at the same elevations, respectively, as stations Nos. 2 and 3. Station No. 3, only a few feet distant from heavy timber to the south, west, and east within 300 feet
backs, but the south slope is more regular. The southerly slope has a grade of nearly 18°, while the opposite northerly slope has a grade of only 10.)°. It is rather level immediately in the vicinity of shelter at No. 2 on northerly slope in the midst of the orchard, but quite steep at point opposite on southerly slope where No. 2a is located in open field over short grass (fig. 20). The shelter at No. 3, because of its location on a northerly slope and proximity to timber, is shut off from prac¬ tically all sunshine.
30442—23 - 2
12
SUPPLEMENT NO. 19.
TRYON.
W. T. Lindsey, Observer.—1 The stations at Tryon, four in number, located about 2 miles to the northwest of the village; station No. 1 (fig. 22), on the valley floor of the Pacolet River, at an elevation of 950 feet'above sea level, the lowest of the experimental stations used in this research; stations Nos. 2 and 3 in the vineyard of the observer, on the southeast slope of Warrior Mountain, and station No. 4 higher up on the slope, with an elpvation of 1,100 feet above station No. 1 and within 400 feet of the summit (figs. 22 and 23). There are several other mountains in the immediate vicinity in the same range, the
station No. 2 is rather steep to the east and southeast, but almost level as station No. 1 is approached; shelter over broken ground with grass and weeds, especially to the north; timber covers most of the slope between stations Nos. 1 and 2, also some timber to the east 50 to 75 feet; vineyard practically surrounded by timber, terraced and fairly steep, but not so steep as immediately below or above. Station No. 3 (fig. 24), 570 feet above station No. 1, on southeast slope about 50 feet above upper rim of vineyard; in a small apple orchard over grass, weeds and rocks; rather a steep slope above to station No. 4, with brush and high timber about 100 to 150 feet to north, northwest, west, and southwest, half encircling station. Station No. 4, 1,100 feet above
ROUND MT,
.WARRIOR
BUCK MT.
jTjor eh
T ryon
Fig. 21. — Tryon, contour map and profile.
most prominent being Tryon Mountain to the northeast, with an eleva¬ tion of 3, 231 feet, while that of Warrior is only 2,465 feet. Then there is Round Mountain, almost midway between Warrior and Tryon. Across the Pacolet valley is Melrose Mountain (see fig. 24), but not near enough nor of sufficient mass to serve effectively as an opposing slope to Warrior Mountain where the research stations were located. Station No. 1, located on the rather wide valley floor of the Pacolet River running in east-west direction, is well situated for the experi¬ mental work, being at the foot of Warrior Mountain, on a grass covered plot on ground practically level. Shelter at the home station, No. 2, on lower edge of vineyard, on southeast slope 380 feet above station No. 1, the horizontal distance being 4,000 feet. The slope below
station No. 1, is on southeast slope on edge of cliff with sharp drop of several hundred feet to station No. 3; is over grass and weeds in small cleared space; timber and brush within 10 to 20 feet on all sides except south and southwest, where sheer drop occurs. From station No. 4 the ground slopes upward rather steep in p laces to the summit of mountain more than 400 feet above. Slope is heavily tim¬ bered above and below station No. 4. The slope, as a whole, from station No. 1 to station No. 4 has an average grade of about 11J°> but immediately above the valley floor, between stations Nos. 1 and 2, the grade is very gentle, while between stations Nos. 2 and 4 the grade is quite steep, especially above station No. 3. The average grade between stations Nos. 2 and 4 is about 26°.
13
THERMAL BELTS AND FRUIT GROWING IN NORTH CAROLINA.
CANE RIVER.
f 06s™-Cane River is located on the northwest
Ll Jk th/oB ai Mountains, and the orchard stations, four in number
the hn«^\2tml eS Wef °fithie V!Ilage’ on the Property of the observer; the base station in a level plot having an elevation of 2,650 feet above
sea level and somewhat above the valley floor of McElroy Creek a branch of Cane River. The summit station is high up on a knob above a steep timbered slope 1,100 feet above the base and about
northerly slope; heavy timber on steep upslope to the south, south- west, and southeast of shelter; some timber also to the east aud west more distant; hills also in those directions 500 or 600 feet away; shelter located over grass-covered surface. Station No. 3, 400 feet above station No. 1, on northerly slope moderately steep; shelter in upper portion of apple orchard near base of mountain in a cove-like inclosure, with grass-covered surface; heavy timber to east, southeast, south, southwest, and west. Sun shut off by timber during early morning and late afternoon hours for the greater portion of the year; steep
1,000 feet distant from Rocky Knob, which stands 250 feet higher. The country throughout this section is rolling and broken and most picturesque, with knobs of various elevations here and there. The two knobs, with generally sharp profile and small mass in proportion to their elevation, are isolated peaks which rise considerably above surrounding peaks within a radius of several miles. Station No. 1, the home station, on a nearly level plot, which was covered with grass in 1913 and 1914; in 1915 and 1916 planted in corn; slope gener¬ ally from north to south, but very slight at station No. 1. Station No. 2, 190 feet above station No. 1, in apple orchard on moderate
upward slope to south and also where timber is located to east; a sharp ascending slope covered with heavy timber from station No. 3 to station No. 4. Station No. 4, 1,100 feet above station No. 1, on knob with steep slope downward from the shelter in every direction, except toward Rocky Knob to south, there being a sag between the two knobs; small timber 10 feet north and west of station No. 4, also 15 to 20 feet northeast; heavy timber beyond in practically all direc¬ tions. The slope, as a whole, from station No. 1 to station No. 4 has an average grade of 16°, being quite gentle below station No. 3 and steep above, the incline above station No. 3 being 24°.
14
SUPPLEMENT NO. 19.
ALTAPASS.
R. F. Brewer , Observer— Altapass is on the main range of the Blue Rid o^e Mountains, the village itself being on the divide directly north of McKinney Gap, with the Black Mountains, including Mount Mitchell, Clingmans Peak, and Celo Mountain standing up at great heights to the west, Grandfather Mountain and Brown Mountain to the east, and smaller knobs in between. The . southeasterly slope containing the experimental stations is steep, while the slope on the other side of the Blue Ridge to the north and northwest is gentle. Five stations here
timber and hills to east and west 200 feet or so. Station No. 3, home station, 500 feet above station No. 1, shelter in peach and apple orchard on sharp southeasterly slope; slope broken into ridges and hogbacks. Station No. 4 (fig. 28), 750 feet above station No. 1; shelter in apple orchard with small trees in vicinity; on steep southeasterly slope; soil badly gullied and worn away here by flood in the summer of 1916. Station No. 5 (fig. 29), 1,000 feet above station No. 1, on summit of ridge 200 feet wide and extending in a northeast-southwest direction and nearly level for a mile or so; shelter in midst of small trees over
are in the orchard of the Holston Corporation, the base station, No. 1, being 2,230 feet above sea level, with the others each 250 feet above its lower neighbor. While the summit station is directly on the main ridge, No. 1 is really on the slope, as the descent below continues 730 feet down to the valley floor at a place called North Cove, two miles distant from station No. 1. Station No. 1 is a small level plot in corn¬ field and surrounded by dense vegetation; timber and hills to west, northwest, and southwest close by; also to east but much farther away; hills to the north. Station No. 2 (fig. 27), 250 feet above station No. 1, in small level plot in cornfield in midst of steady southeasterly slope;
grass and weeds, in marked contrast to the comparatively bare soil at the stations lower down on the slope, as shown in figure 28, where the vegetal cover is thin because of the steepness. The slope becomes steadily steeper from station No. 1 to summit and is especially steep between stations Nos. 4 and 5. The average grade of entire slope from station No. 1 to station No. 5 is about 16° and is probably more regular and uniform than any other long slope, except Ellijay; which has an average grade of 19°. The entire Altapass slope, including that below station No. 1, is about 1,730 feet in height, and the Ellijay slope is 1,760 feet.
THERMAL BELTS AND FRUIT GROWING IN NORTH CAROLINA.
BLOWING ROCK.
15
E G. Underdown, Observer.— The village of Blowing Rock is 1 neat pH
tL creTL thGprridfa Rer/l0Untain (fig 31) on the P^ateau f,UEh «'ith tiie crest of the Blue Ridge, running parallel there to the Tennessee
boundary line and distant from it about 10 miles. The plateau here
" e, a® at Highlands, close to the Georgia boundary, averages more
£?*’™«** m elevation. To the west and south of' the village there
s a sharp descent to the valley of the Johns River, and beyond as far
IpnlTn.r T nreit0ICring mo,mtaills- On the plateau itself are lnobsA°i whlc.h rnV0 °nes lie 1° the north of the
1 lage, Pine Ridge and Flat Top, with elevations of 4,400 feet and 4,590
grassy plot, 4o0 feet above No. 1, on rather steep southerly slope broken up into ridges and hogbacks, so that while the general slope is south and southeast the local slopes in the orchard vary. The orchard extends upward from station No. 2, with a rather uniform steepness, the average slope in this orchard is about 15°. The slope extends 320 feet above ho. 2 and 1,130 feet below No. 1, in all a vertical height of about 1,800 feet, even greater than those at Altapass and Ellijay, but for purposes of the discussion this slope will not be classed with the erm°ng s*°Pes because of lack of suitable observation stations. The llat Top orchard (figs. 32 and 33) is shaped much like an amphitheater which gradually slopes down from the upper rim to a lake or large pond at the base. The basin is mostly inclosed, and the descent at the outlet
feet, respectively. The experimental stations are five in number, divided into two groups, three in the Flat Top orchard and two in the China orchard, both apple orchards, and owned by Mrs. Abram Cohn, located, respectively, from 1 to 2 miles north and northwest of the village, and distant from each other about one-half mile. In these two and the Green Park orchard, another property of the Cohn family in the vicinity, are approximately 40,000 apple trees, the three combined being probably the largest property of the kind in the East. The China orchard, containing stations Nos. 1 and 2, is on a steep and narrow southerly slope which drains into the Johns River. Station No. 1, elevation 3,130 feet above sea level; shelter over sod on southerly slope; timber on sharp slopes to east, southeast, southwest, and west from 30 to 50 feet from shelter. The slope continues downward from the China orchard to a ravine far below. Station No. 2, in rough
is gradual. The orchard is broken up into moderate ridges and saddles, but generally all slopes lead toward the lake, while beyond hills and slopes extend in different directions with small gaps between the hills. Station No. 3 in the Flat Top orchard has an elevation of 3,580 feet, the same as No. 2 in the C hina orchard, and is on the valley floor, near a large pond or lake, shown in figure 33, on an almost level surface over rather thick grass. The ground at station No. 3 slopes gradually up¬ ward to the northwest to a smaller pond, a steep slope beginning im¬ mediately beyond and rising in a northwesterly direction to stations Nos. 4 and 5. There are sharp slopes on both sides of station No. 3 to the east and northeast and the west and northwest, respectively, the slope on the east side being distant about 25 feet, while that on the west is about 100 feet. Station No. 4, 175 feet above station No. 3, over grass on moderate slope in midst of apple trees; the slopes curve around more
16
SUPPLEMENT NO. 19.
or less brokenly tending on one side downward toward the east and on the other toward the west or southwest. Station No. 5, 350 feet above station No. 3, the home station; located on upper rim of orchard just below roadway near the residence of owner. Shelter is over long grass. From this station the orchard stretches down in all directions, except to the northeast, north, and northwest. The average slope from station No. 3 to station No. 5 in the Flat Top orchard is less than 9°,
compared with the slope of 15° between Nos. 1 and 2 in the China orchard. There is a large extent of surface area in the vicinity of No. 5 approximately at the same level, and the surroundings are much unlike the knobs on which several of the summit research stations were located. No. 3 is the valley floor station for the Flat Top group at Blowing Rock, just as No. 3 at Highlands is the valley floor station of the Waldheim group.
Fig. 35. — Globe, contour map and profile.
GLOBE.
Julius L. Gragg, Observer. — Globe, with its group of three stations, is located in the midst of mountains, Grandfather Mountain to the north¬ west and Brown Mountain to the southwest. The Summit station is on the southeasterly slope of a spur of Grandfather, called Snake Den Mountain. The valley of Gragg Fork, in which the base station is located, is here narrow and winding and reaches generally in a north¬ west-southeast direction; but below, the direction is more southerly, draining the northern portion of the eastern slope of Grandfather Moun¬ tain. The slopes are steep on both sides of the valley, except in the lower levels of the mountain, where the slope is gradual. Station No. 1, the home station, 1,625 feet above sea level, on a level grass plot across Gragg Fork from the base of mountain, shade trees in yard about
25 feet distant from shelter to the north; south aud east is timber about 300 feet distant and to the west about 600 feet. Station No. 2, 300 feet above station No. 1, in small orchard on east to southeast slope; shelter in small patch of cleared land surrounded by timber 200 to 300 feet distant on side of mountain on moderate slope, but steep above and below; sunshine cut off early in afternoon, especially in late fall and winter. Station No. 3. on summit of ridge 1,000 feet above station No. 1 on Snake Den Mountain; shelter in clearing surrounded by brush and timber about 20 feet distant in all directions; grade steep up the mountain from station N o. 2 to station No. 3. Timber covers practically the entire mountain; peaks all-around. The entire slope from station No. 1 to station No. 3 averages about 13°, but that from station No. 2 to station No. 3 averages more than twice this— 28°.
THERMAL BELTS AND
FRUIT GROWING IN NORTH CAROLINA.
17
gorge.
Mountain and^ the! 25?W*"^Gor?e is located at the base of Brown lountain and the stations, five in number, reach along the Black
^onpBdnwCh UPi \he- S 0-Pe t0 the summit of Little Chestnut Knob, the slope downward being in a general northeasterly direction. The main
peak of Brown Mountain is distant about a half mile to the southeast with a sag between. The region is quite mountainous, but there are
the Blue RidrJeaiieftgeh^ln the/,mmediate vicinity. The main chain of the Blue Ridge lies to the north, northwest, and west of Brown Moun¬ tain. Station No. 1 the home station, 1,400 feet above sea level in the valley floor of Wilson Creek, is in a gap close to Black Bee Creek
farther away. Although the general slope on this side of the mountain is northeasterly, the ground is so broken at No. 3 the slope turns there to the southerly, thus forming a cove or pocket partly inclosed, with sunshine cut off m the afternoon. Station No. 4 (old), 840 feet above No; 1, in an abandoned orchard on the north slope on a hogback which slopes off gently to the east and west; in the midst of brush, apple and other small trees, and 20 to 30 feet away from larger timber but none very large ; station in operation in 1913 and 1914 only. Station No. 4 (new), 840 feet above No. 1, in operation in 1915 and 1916, located on a moderate northerly slope in clearing over thin grass, although the general slope is northeasterly. Station is surrounded by trees of dif¬ ferent heights at distances varying from 60 to 125 feet; small brush all
and a short distance west of Wilson Creek, into which Black Bee empties. The gap runs from west to east between hills for 500 feet. The station, over comparatively bare soil and on rather level plot with brush close at hand, is surrounded by hills and mountains, with timber. Sta¬ tion No. 2, in Bagley orchard, 290 feet above station No. 1, on north¬ easterly slope, about 50 feet east of Black Bee Creek. The valley here runs from southwest down to northeast and is surrounded by hills, this location partaking of base station conditions. Surface under shelter rather bare; slope up from No. 1 to No. 2 gentle, as is, in fact, almost the entire slope. Station No. 3, 615 feet above No. 1 in Chestnut Hollow Cove, on moderate north to south slope; timber is rather thin and 100 to 300 feet distant in all directions. Hills and mountains are
around. This station is distant about 4,500 feet in a horizontal direc¬ tion from the old No. 4, and was substituted for it at the close of 1914 be¬ cause of the inconvenience in reaching the old location. Station No. 5, 1,040 feet above station No. 1; shelter on Chestnut Knob in midst of brush; sparse timber distant 20 to 30 feet in all directions; knob slopes off on all sides, there being a level space of about 30 feet square on the top where shelter stands. The timber around station No. 5 does not cast nearly as much shade as at station No. 4. For a long slope, Gorge is the most gradual of all employed in this research, the horizontal distance between the base and the summit stations being about 2 miles for a vertical distance of 1,040 feet. The entire slope from base to summit averages only 6°.
18
SUPPLEMENT NO. 19.
TRANSON.
Sidney M Transon, Observer. — Transon is in the extreme northern portion of the Carolina Blue Ridge region at a considerable elevation, the lowest of the experimental stations in the group of four stations being 2 970 feet above sea level. The country m the immediate vicinity is rolling and broken with peaks here and there m the distance
tion No. 3, 300 feet above station No. 1, has much the same exposure as No. 2, over grass; rather flat surface with general westerly gradual slope; some timber about 300 feet to the south. Station No. 4, 450 feet above station No. 1, in a flat grassy plot on a small knob. Almost the entire slope is gradual, except immediately below station No. 4. Stations Nos. 1, 2, and 3, are in the same straight line, and for a vertical
although not so mountainous as the sections farther south. The stations are on the property of the observer. The base station, No. 1, 2,970 feet above sea level; the home station, on a level grass plot in a cove on the westerly slope about 300 feet above the valley floor of Peak Creek; no timber in the immediate vicinity. Station No. 2, over grass, also on the west slope 150 feet higher up, the ground being rather flat where the shelter stands and the general slope gradual. Sta-
difference of 300 feet between stations Nos. 1 and 3 there is a horizontal distance of about 3100 feet. While the general slope is westerly, it is not a steady decline from station No. 4 to the base, there being some small secondary hills or humps on the way. Above, as well as below, station No. 3, for instance, the ground descends, and also at station No. 2, but to a lesser extent. The entire slope between stations Nos. 1 and 4 averages about 8°.
THERMAL BELTS AND FRUIT GROWING IN NORTH CAROLINA.
WILKESBORO.
John Johnston, Observer.— Wilkesboro is considerbly east of the Blue Ridge, m the valley of the Yadkin to the north of the Brushy Mountains The principal town there is now called North Wilkesboro, but the ex¬ perimental stations, four in number, on the north slope of the Brushy Mountains, are nearer to the old town of Wilkesboro. The stations are in the orchard of Dr. Charles A. Willis and lie on a moderate northerly
in apple orchard across road just below station No. 3, on moderate slope with grass covered soil. Station No. 3, 350 feet above station No. 1, on northerly slope, on knob in orchard over weedy surface; sag between it and station No. 4; ground flat around shelter for 100 to 200 feet or more then slopes off all directions. Station No. 4, 430 feet above station No. 1, on grass covered soil in apple orchard on rather level ridge, extending north and south and about 130 feet below summit, of the
slope at a point about midway between Nos. 15_ and 38, as shown on the relief map. Station No. 1, with an elevation of 1,240 feet above sea level, about 300 feet above the valley floor of the Yadkin, on a bench a few hundred feet in extent on a northerly slope. The ground in vicinity of station No. 1 is rather uneven and almost bare of grass and about 400 feet distant to the north descends to the valley floor below; some timber to the west of shelter, 1,000 feet, and to the east, 120 feet. Station No. 2, on notherly slope, 150 feet above station No. 1; shelter
Brushies, which lie to the south about 1,000 feet or more across a sag running west to east. A short distance to the north is a sharp slope downward; directly east and west of shelter is a slope downward to broken country, and to the south 200 to 300 feet there is considerable timber. Below to north, northeast, and northwest lies a broad valley or level plain extending 20 to 30 miles to the Blue Ridge beyond. The differences in elevation between these stations are slight; the grade between Nos. 1 and 3 is 13° and between Nos. 1 and 4, 8°.
20
SUPPLEMENT NO. 19.
MOUNT AIRY.
J. A. Sparger, Observer. — -Mount Airy, close to the Virginia border, is of course, even farther than Wilkesboro from the main mountain re¬ gion, and in the viinity there are only a few spurs or peaks, and these are of rather slight elevation. The experimental stations here, four in number, are on the property of the Sparger Orchard Co., about 6 miles east of the city of Mount Airy, on Slate Mountain, station No. 1 at the base, stations Nos. 2 and 3 on the western and eastern slopes,
directions is rather flat, but the land becomes rolling as the mountain is approached. Station No. 2, in orchard in cultivated area, 160 feet above station No. 1, on fairly steep westerly slope, with timber 150 feet upslope; the land on this slope somewhat broken to the north and south; slope to the south rather moderate, but steep to north from a point 30 feet from shelter. Station No. 3, on easterly slope, with the same elevation as station No. 2; slope more gradual as compared with the westerly slope; not in orchard but on rough weedy ground, and between it and the summit is a belt of timber. Station No. 4
respectively, and station No. 4 at the summit. Slate Mountain overlooks the city of Mount Airy, which stands on a broad plain to the west. Distant 10 to 20 miles farther west are the Sorrytown Mountains, a branch of the Blue Ridge, extending in a southwesterly direction and across the Yadkin to the southwest, 30 miles or more away are the Brushy Mountains. To the east is a broken country for 15 to 30 miles with several spurs of varying heights. Station No. 1 (fig. 40), the home station, 1,340 feet above sea level, on a level plot of grass, some¬ what distant from the base of the mountain on which the orchard is located. The country near station No. 1 for several hundred feet in all
(fig. 41), in orchard 360 feet above station No. 1, is on the summit of the ridge 200 feet across and almost level, with slight slopes leading thence directly toward the west and east. The ridge runs from north¬ east to southwest 1 mile, undulating somewhat brokenly; a portion of the ridge to the northeast about a quarter of a mile away is about 30 feet higher than shelter No. 4. Horizontal distance between station No. 3 and the summit is nearly three times as great as the distance between the summit and station No. 2. The average grade on the westerly slope between stations Nos. 2 and 4 is 16°, as compared with the average grade on the easterly slope between stations Nos. 3 and 4 of 10°.
THERMAL BELTS AND FRUIT GROWING IN NORTH CAROLINA.
21
ARRANGEMENT OF TABLES.
It is necessary to limit the publication of the tabular matter to the smallest size consistent with an under¬ standing of the problems under consideration. If only a few slopes were under investigation, it might have been possible to publish the data in greater detail, as there would then have been a relatively small number of stations involved; but in this case we shall have to be content for the most part with summarized tables, except when it becomes necessary in expounding certain theories to give daily and hourly values.
The average maximum, average minimum, absolute maximum, and absolute minimum temperature, and the absolute and average range and mean temperature will be discussed in the order named, and then will follow special chapters on inversion and norm conditions, frosts, lengths of the growing season, and a few supple¬ mentary studies bearing upon the situation. Graphs have been employed to emphasize special features, and it is thought that those, together with the tables, will be considered sufficiently comprehensive.
Physical explanation of local variation in temperature. — Before taking up the discussion of the observational data or dealing with the question of temperature and circulation within the valleys, it appears highly important to present in a connected form a somewhat comprehensive explanation of the causes of the conditions which the observations disclose.
It must be recognized that the progressive changes of temperature from hour to hour and from day to day at
any one locality result from a great many causes, but our present problem is chiefly concerned with changes going on between daytime and nighttime in mountain valleys at times when the atmosphere is clear and little or nor wind prevails, especially at night. Even in the daytime on these occasions the motions of the atmosphere are more or less dominated by local influences rather than the general cyclonic or anticyclonic circulation and changes of temperature are then due primarily to solar insolation in the daytime and radiation at night.
It is well known that atmospheric absorption and radiation, especially when the atmosphere is relatively dry or free from clouds, are very small. Important changes of temperature are then brought about chiefly by contact with the earth’s surface, which is warm or cold according to circumstances. It is important to recognize that on this account we must regard the walls and floors of valleys as the primary heating agency of the atmosphere during the daylight hours, and, conversely, during the nighttime these same walls and floors are the primary cooling agencies by reason of the active loss of tempera¬ ture by the surface cover and vegation of the walls, due to nocturnal radiation.
The processes by which the heating in the daytime and the cooling which occurs at nighttime communicate heat to the atmosphere or receive heat from the atmos¬ phere are the phenomena which we will try to make clear in the interpretation of such observational data as have been collected in this study.
■
.
.
:
23
THERMAL BELTS ANB FRUIT GROWING IN NBRTH CAROLINA.
TEMPERATURE.
MAXIMUM TEMPERATURE.
In the discussion of average maximum temperature Table 1 is supplemented by Tables la, lb, lc, and Id.
The avearge maximum readings contained in these tables are deduced from the maxima observed during the daytime only, instead of the 24-hour maxima, just as later in the discussion of the mean minimum temperature night minima only are used. This plan has been adopted in order to make possible comparisons of day conditions, on the one hand, and of night conditions, on the other,
and the influence of maxima that occurred in the nighttime or minima in the daytime will thus be eliminated.
The maxima in the mountain region vary considerably because of difference in latitude, elevation above sea level, character of the weather, whether cloudy or sun¬ shiny, shade from neighboring timber, hills, or mountains, the direction and degree of inclination of the slope, the seasonal variation of the sun, the character and amount of vegetal cover, and the absolute and relative humidity of the air.
Table 1. — Monthly and annual average maximum temperatures, 1913-1916.
[The differences between the averages at the base station and those of the respective slopes may be seen by simple inspection.)
|
Principal and slope stations elevation above mean sea level of base station (feet). |
Height of slope sta¬ tion above base (feet). |
Janu¬ ary. |
Febru¬ ary. |
March. |
April. |
May. |
June. |
|
Altapass: No. 1, base station, eleva¬ tion 2, 230 . |
'47.4 |
1 47.3 |
150.7 |
65.7 |
75.0 |
79.3 |
|
|
No. 2, SE . |
250 |
1 46.6 |
146.4 |
1 49.6 |
64.8 |
74.6 |
79.0 |
|
No. 3, SE . |
500 |
144.9 |
1 44.7 |
1 48. 0 |
63.3 |
73.2 |
77.4 |
|
No. 4, SE . |
750 |
1 43.9 |
1 43.4 |
1 47.4 |
62.0 |
71.8 |
76.1 |
|
No. 5, summit . |
1,000 |
1 43. 1 |
142.7 |
1 46.6 |
61.5 |
70.8 |
75.3 |
|
Asheville: No. 1, base station, eleva¬ tion 2,445 . |
50.8 |
48.2 |
52.2 |
64.8 |
75.2 |
79.5 |
|
|
No. 2, N . |
155 |
49.4 |
46.7 |
51.2 |
64.0 |
74.8 |
78.8 |
|
No. 2a, S . |
155 |
50.1 |
47.7 |
51.5 |
63.9 |
74.0 |
78.2 |
|
No. 3, N . . |
380 |
47.0 |
44.9 |
49.6 |
63.0 |
72.8 |
75.9 |
|
No. 3a, S . |
380 |
51.0 |
48.8 |
52.9 |
66.3 |
75.6 |
79.2 |
|
Blantyre: No. 1, base station, eleva¬ tion 2,090 . |
52.5 |
51.2 |
55.8 |
68.2 |
78.0 |
82.0 |
|
|
No. 2, NW . |
300 |
50.8 |
49.3 |
54.3 |
67.7 |
77.8 |
81.4 |
|
No. 3; NW . |
450 |
50.7 |
49.2 |
52.4 |
67.1 |
77.3 |
80. S |
|
No. 4, NW . |
eoo |
51.3 |
51.0 |
54.6 |
68.9 |
77.9 |
81.6 |
|
Blowing Rock: No. 1, base station, eleva- |
44.5 |
42.5 |
46.4 |
59.0 |
69.8 |
74.4 |
|
|
No. 2, S . |
450 |
44.0 |
42.5 |
46.1 |
59.0 |
69.2 |
74.2 |
|
No. 3, SE . |
450 |
42.8 |
41.2 |
44.7 |
58.2 |
68. 2 |
73.2 |
|
No. 4, SE . |
625 |
43.5 |
41.8 |
45.1 |
57.8 |
68.2 |
73.4 |
|
No. 5, SE . |
800 |
43.0 |
40.6 |
44.8 |
57.8 |
67.7 |
73.0 |
|
Bryson: No. 1, base station, eleva- |
2 52. 2 |
151.3 |
154.1 |
69.0 |
79.2 |
83.5 |
|
|
No. 2, h . |
385 |
2 50. 6 |
151.1 |
1 54.1 |
68.9 |
79.4 |
82.8 |
|
No. 2a, S . |
385 |
2 52. 3 |
152.2 |
155.1 |
69.8 |
79.7 |
82.9 |
|
No. 3, summit . |
570 |
2 51.1 |
152.1 |
155.9 |
72.7 |
81.6 |
84.1 |
|
Cane River: No. 1, base station, eleva- |
1 47.9 |
146.0. |
148.5 |
63.6 |
74.1 |
78.5 |
|
|
No. 2, N . |
190 |
1 46.9 |
1 45. 5 |
14S. 2 |
63.3 |
73.9 |
78.4 |
|
No. 3, NE . |
400 |
143.2 |
1 42.6 |
1 46.7 |
62.8 |
73.5 |
77.4 77.2 |
|
1,100 |
144.1 |
1 42.9 |
1 46.1 |
62.6 |
74.6 |
||
|
Ellijay: No. 1, base station, eleva- |
151.4 |
151.0 |
153.6 |
68.1 |
78.1 |
81.8 |
|
|
No. 2, N . |
310 |
1 50.2 |
1 50.2 |
1 52.9 |
67.1 |
77.1 |
80. 8 79.0 76.8 1 75.3 |
|
No. 3^ N . |
620 |
149.1 |
148.6 |
151.3 |
64.9 |
75.0 |
|
|
No. 4,' N . |
1,240 |
1 45. 0 |
145.1 |
148.4 |
63.5 |
73.6 |
|
|
1,760 |
2 45. 8 |
2 46.0 |
1 48.2 |
1 63.0 |
172.7 |
||
|
Globe: No. 1, base station, eleva- |
50.5 |
50.0 |
54.8 |
67.9 |
78.2 |
82.2 |
|
|
No. 2, E . |
300 |
48.2 |
49.0 |
54.0 |
67.8 |
77.4 |
80. 1 80.1 |
|
1,000 |
48.0 |
48. 2 |
53.1 |
67.3 |
77.4 |
||
|
Gorge: No. 1, base station, eleva- |
50.0 |
50.5 |
56.3 |
69.7 |
80.3 |
83.9 82.0 79.8 80.8 80.1 |
|
|
No. 2 'l^E . |
290 |
50.2 |
49.6 |
54.8 |
68.0 |
78.5 |
|
|
No. 3* S . |
615 |
49.1 |
48.2 |
53.6 |
66. 4 |
76.4 |
|
|
No. i) N. (old); NE. (new).. |
840 1, 040 |
48.5 48.0 |
4S.0 47.9 |
53.3 53.1 |
67.1 67.0 |
77.4 76.8 |
|
|
Hendersonville: No. 1, base station, eleva- |
>48.9 |
149.8 |
153.4 |
67.2 |
76.7 |
80.6 78.5 77.5 77.2 |
|
|
450 |
147.0 |
147.0 |
1 50. |
64.6 |
74. 6 |
||
|
Nn 3' E . |
600 |
1 47. 1 |
146.6 |
1 49.7 |
63.8 |
73.7 |
|
|
750 |
1 46.0 |
145.9 |
1 49.0 |
63.3 |
73.4 |
||
|
Highlands: No. 1, base station, eleva¬ tion, 33150 . No 2 SE . |
. 266" |
145.9 147.3 |
144.1 147.4 |
148.6 147.9 |
62.8 62.6 |
72.4 73.0 73.0 70.5 70.8 |
75.9 76.2 73.8 73.9 74.4 |
|
No. 3^ SE . |
325 |
M3. 1 |
142.9 |
146.1 |
60.7 60.1 |
||
|
No. A, SE . |
525 |
143. 1 |
1 42.0 |
1 44.2 |
|||
|
No. 5, SE . |
725 |
142.7 |
141.9 |
1 43. 6 |
60. 4 |
||
|
Mount Airy: No. 1, base station, eleva- |
49.7 |
48.7 |
54.6 |
68.4 |
78.5 78.1 77.4 77.2 |
84.6 |
|
|
Nn 2 W . |
160 |
48.4 |
147.2 |
53.6 |
67.2 66.8 1 66.9 |
||
|
No 3 E . |
160 |
48.8 |
47.4 |
! 53.7 |
82.1 |
||
|
360 |
47.6 |
47.0 |
1 53. 5 |
||||
|
1 3-year average. |
|
July. |
I August. |
Septem¬ ber. |
October. |
Novem¬ ber. |
Decem¬ ber. |
Annual. |
|
82.0 |
81.2 |
74.9 |
68.2 |
58.6 |
46.8 |
64. S |
|
81.1 |
80.2 |
74.8 |
67.9 |
57.6 |
46.2 |
64. 1 |
|
79.2 |
78.4 |
72.7 |
65.4 |
55.8 |
44.6 |
62.3 |
|
78.1 |
77.6 |
71.3 |
64.7 |
55.2 |
43.1 |
61.2 |
|
77.7 |
76.9 |
71.2 |
63.8 |
54.6 |
43.0 |
60.6 |
|
81.9 |
81.5 |
76.2 |
68.2 |
59.0 |
47.6 |
65.4 |
|
81.1 |
‘80.2 |
174.8 |
66.1 |
56.9 |
46.0 |
64.2 |
|
80.4 |
80.2 |
75.3 |
67.2 |
58.2 |
47.3 |
64.5 |
|
78.0 |
76.8 |
70.4 |
62.4 |
53.8 |
43.6 |
61.5 |
|
81.2 |
80.3 |
74.8 |
67. S |
60.6 |
48.3 |
65.6 |
|
83.8 |
82.5 |
76.4 |
68.7 |
60.2 |
48.2 |
67.3 |
|
82.9 |
81.5 |
75.4 |
68.2 |
59.5 |
47.4 |
66.4 |
|
82.4 |
81.1 |
74.8 |
68.3 |
59.7 |
47.4 |
66.1 |
|
83.0 |
82.3 |
76.7 |
69.5 |
60.8 |
4S.0 |
67.2 |
|
76.8 |
75.6 |
69.9 |
62.4 |
52.9 |
42.0 |
59.7 |
|
76.1 |
74.4 |
69.3 |
61.8 |
53.0 |
42.3 |
59.4 |
|
75.1 |
73.8 |
68.0 |
61.2 |
51.8 |
41.3 |
58.3 |
|
75.8 |
74.6 |
68.9 |
61.4 |
52.5 |
42.2 |
58.8 |
|
75.4 |
74.2 |
68.3 |
60.8 |
51.6 |
41.3 |
58.2 |
|
85.6 |
84.9 |
79.8 |
71.4 |
1 61.4 |
1 48.3 |
68.4 |
|
84.8 |
84.2 |
79.2 |
70.4 |
* 59.8 |
‘46.4 |
67.6 |
|
84.7 |
83.8 |
79.0 |
71.4 |
161.6 |
* 48.2 |
68.4 |
|
84.9 |
84.0 |
78.6 |
70.1 |
1 60.2 |
1 46.3 |
68.5 |
|
81.3 |
80.7 |
75.1 |
66.9 |
57.2 |
45.7 |
63.8 |
|
80.6 |
79.7 |
73.8 |
66.0 |
56.9 |
45.1 |
63.2 |
|
79.2 |
77.6 |
70.8 |
61.9 |
52.0 |
41.4 |
60.8 |
|
79.0 |
77.4 |
70.7 |
62.8 |
54.4 |
42.9 |
61.2 |
|
83.8 |
83.1 |
78.2 |
70.3 |
61.3 |
49.8 |
67.5 |
|
82.9 |
81.8 |
77.2 |
68.9 |
60.0 |
48.6 |
66.5 |
|
81.0 |
80.0 |
74.6 |
67.4 |
58.6 |
47.7 |
64.8 |
|
79.0 |
78.2 |
72.5 |
64.6 |
155.1 |
44.1 |
62.2 |
|
177.0 |
‘76.8 |
1 72.1 |
1 64.4 |
155.0 |
1 44.1 |
‘61.7 |
|
84.5 |
82.8 |
77.1 |
70.4 |
60.8 |
48.4 |
67.4 |
|
1 82.1 |
1 81.3 |
75.3 |
68.1 |
58. 1 |
45.5 |
65.6 |
|
82.1 |
80.4 |
74.2 |
67.3 |
58.4 |
45.8 |
65.2 |
|
86.3 |
84.0 |
77.8 |
70.9 |
60.8 |
47.4 |
68.2 |
|
84.5 |
83.4 |
77.4 |
69.6 |
60.0 |
47.2 |
67.1 |
|
82.4 |
81.0 |
75.2 |
68.4 |
59.4 |
46.7 |
65. 6 |
|
82.7 |
81.4 |
74.6 |
67.6 |
57.9 |
45.9 |
65.4 |
|
82.2 |
80.4 |
73.7 |
66.4 |
58.4 |
45.4 |
65.0 |
|
83.0 |
81.2 |
75.0 |
68.0 |
59.1 |
47.2 |
65.8 |
|
80.7 |
79.2 |
73.3 |
65.9 |
57.1 |
45.9 |
63.7 |
|
80.2 |
78.5 |
72.4 |
64.8 |
56.5 |
45.0 |
63.0 |
|
79.8 |
78.6 |
72.6 |
65.0 |
56.2 |
44.6 |
62.6 |
|
77.6 |
76.8 |
71.6 |
64.4 |
56.6 |
45.8 |
61.9 |
|
77.4 |
77. 1 |
71.8 |
64.6 |
56.2 |
40. 6 |
62. 5 |
|
75.4 |
75.1 |
69.2 |
62.4 |
54.4 |
43.9 |
60.0 |
|
75.8 |
76.2 |
68.6 |
61.5 |
53.8 |
42.8 |
59.4 |
|
76.5 |
75.4 |
69.2 |
‘62.2 |
54.6 |
43.5 |
5y. 6 |
|
85.8 85.2 |
83.0 82.4 |
77.7 77.1 |
69.5 68.8 |
59.2 58.2 |
46.7 45.5 |
67.2 66.3 |
|
84.8 84.2 |
82.3 81.7 |
77.0 75.9 |
68.4 67.9 |
58.2 57.8 |
46.2 45.4 |
66. 1 65.6 |
2 2-year average.
24
SUPPLEMENT NO. 19.
Table 1. — Monthly and annual average maximum temperatures, 1918-1916 — Continued.
[The differences between the averages at the base station and those of the respective slopes may be seen by simple inspection.]
|
Principal and slope stations elevation above mean sea level of base station (feet). |
Height of slope sta¬ tion above base (feet). |
Janu¬ ary. |
Febru¬ ary. |
March. |
April. |
May. |
June. |
July. |
August. |
Septem¬ ber. |
October. |
Novem¬ ber. |
Decem¬ ber. |
Annual. |
|
Transon: No. 1, base station, eleva- |
46.2 |
43.8 |
48.4 |
61.8 |
71.9 |
77.1 |
79.6 |
78.1 |
72.7 |
65.2 |
54.6 |
43.8 |
61.9 |
|
|
No. 2, W . |
150 |
44.1 |
48.0 |
46.3 |
60.2 |
69.8 |
75.2 |
77.0 |
75.8 |
69.3 |
61.6 |
52.4 |
41.2 |
59.8 |
|
No. 3, W . |
300 |
44. 1 |
42.0 |
46.4 |
60.7 |
70.2 |
75.7 |
77.8 |
76.1 |
70.7 |
62.9 |
52.7 |
41.2 |
60.0 |
|
No. 4, Summit . |
450 |
1 41.4 |
141.1 |
i 43.5 |
58.4 |
68.1 |
73.9 |
76.1 |
75.1 |
69.8 |
60.7 |
51.3 |
40.3 |
58.4 |
|
Tryon: No. 1, base station, eleva- |
54.6 |
54.3 |
59.2 |
71.7 |
81.4 |
86.2 |
88.6 |
86.7 |
80.9 |
74.0 |
63.8 |
51.8 |
71.1 |
|
|
No. 2, SE . |
380 |
53.4 |
53.9 |
59.0 |
72.0 |
81.4 |
83.4 |
88.1 |
86.2 |
80.6 |
73.2 |
63.9 |
51.5 |
70.6 |
|
No. 3, SE . |
570 |
52.0 |
51.9 |
56.3 |
69,2 |
78.8 |
80.7 |
85.1 |
83.8 |
77.6 |
68.9 |
60.7 |
48.7 |
68.0 |
|
No. 4, SE . |
1,100 |
51.6 |
.50.7 |
55.4 |
68.0 |
77.1 |
79.0 |
84.2 |
82.9 |
77.0 |
70.4 |
61.1 |
48.5 |
67.3 |
|
Wilkesboro: No. 1, base station, eleva¬ tion, 1,240 . |
51.4 |
50.4 |
56.3 |
69.8 |
79.4 |
85.2 |
87.5 |
84.9 |
79.2 |
71.8 |
61.1 |
48.6 |
68.8 |
|
|
No. 2, N . |
150 |
50.6 |
49.8 |
55.8 |
69.5 |
79.7 |
84.6 |
87.2 |
84.3 |
77.6 |
70.0 |
60.0 |
46.9 |
68.0 |
|
No. 3, N . |
350 |
50.6 |
49.3 |
55.4 |
68.1 |
78.0 |
82.7 |
84.9 |
82.7 |
76.0 |
69.0 |
59.4 |
47. 1 |
66.9 |
|
No. 4, W . |
430 |
50.0 |
48.6 |
54.6 |
68.0 |
76.8 |
82.1 |
84.5 |
82.6 |
75.7 |
68.0 |
59.2 |
46.7 |
66.4 |
1 3-year average.
3 2-year average.
Table ia. — • Average maximum temperatures during selected clear
periods.
[The differences between the averages at the base station and those of the respective slope stations may be seen by simple inspection.)
|
Principal and slope stations; elevation above mean sea level of base station (feet). |
Height of slope station above base (feet). |
Clear period— May 19-26, in¬ clusive, 1914. |
Clear period — Nov. 1-7 and 22-26, inclusive. 1914. |
|
Altapass: |
|||
|
SO. 6 |
64.3 |
||
|
No. 2, SE . |
250 |
80.1 |
63.7 |
|
No. 3, SE . |
500 |
78.8 |
61.3 |
|
No. 4, SE . |
750 |
77.9 |
60.9 |
|
No. 5, summit . |
1,000 |
76.1 |
59.8 |
|
Asheville; |
|||
|
81.0 |
62.2 60.0 |
||
|
No. 2, N . |
155 |
80.4 |
|
|
No. 2a, S . |
155 |
78.4 |
62.8 |
|
No. 3, N . |
380 |
77.5 |
56.2 |
|
No. 3a, S . |
380 |
80.6 |
67.6 |
|
Blantyre; |
|||
|
No. 1, base station, elevation 2,090 . |
83.0 |
66.4 65.6 |
|
|
No. 2, NW . |
300 |
84.1 |
|
|
No. 3, NW . |
450 |
83.5 |
65. 5 |
|
No. 4, NW . |
600 |
84.6 |
66.5 |
|
Blowing Rock; |
|||
|
No. 1, base station, elevation 3,130 . |
75.8 |
58.0 58.1 |
|
|
No. 2, S . |
450 |
74.0 |
|
|
No. 3, SE., . |
450 |
73.1 |
55.8 |
|
No. 4, SE . |
625 |
73.5 |
58.2 |
|
No. 5, SE . |
800 |
72.8 |
55.9 |
|
Bryson: |
|||
|
No. 1, base station, elevation 1,800 . |
84.7 |
67.4 65.5 |
|
|
No. 2, N . |
385 |
84.9 |
|
|
No. 2a, S . |
385 |
84.5 |
67.8 |
|
No. 3, summit . |
570 |
86.0 |
65.5 |
|
Cane River: |
|||
|
No. 1, base station, elevation 2,650 . |
79.8 |
61.2 60.8 |
|
|
No. 2, N . |
190 |
78.8 |
|
|
No. 3, NE . |
400 |
78.6 |
56.0 |
|
No. 4, summit . |
1,100 |
81.8 |
58.3 |
|
Ellijay: |
|||
|
No. 1, base station, elevation 2,240 . |
80.9 |
66.2 |
|
|
No. 2, N . |
310 |
82.1 |
63.8 |
|
No. 3, N . |
620 |
79.1 |
63.6 |
|
No. 4, N . |
1,240 |
78.8 |
58.8 |
|
No. 5, summit . |
1,760 |
77.5 |
60.3 |
Table la. — Average maximum temperatures during selected clear periods — Continued.
[The differences between the averages at the base station and those of the respective slope stations may be seen by simple inspection.]
|
Principal and slope stations: elevation above mean sea level of base station (feet). |
Height of slope station above base (feet). |
Clear period — May 19-26, in¬ clusive, 1914. |
Clear period — Nov. 1-7 and 22-26, inclusive, 1914. |
|
Globe: |
|||
|
No. 1. base station, elevation 1,625 . |
84.0 |
67. 2 |
|
|
No. 2, E . . . . |
300 |
83.8 |
62.0 |
|
No. 3, summit . |
1,000 |
83.9 |
65.3 |
|
Gorge: |
|||
|
No. 1, base station, elevation 1,400 . |
87. 1 |
67.8 66.2 |
|
|
No. 2, NE . |
290 |
85.2 |
|
|
No. 3, S . |
615 |
82.9 |
66.0 |
|
No. 4, NE . |
840 |
83.2 |
67.1 |
|
No. 5, summit . |
1,040 |
82.6 |
65.5 |
|
Hendersonville: |
|||
|
No. 1, base station, elevation 2,200 . |
82.6 |
65. 2 |
|
|
No. 2, E . |
450 |
81.0 |
61.9 |
|
No. 3, E . |
600 |
79.6 |
62.0 |
|
No. 4, summit . |
750 |
79.0 |
61.5 |
|
Highlands: |
|||
|
No. 1, base station, elevation 3,350 . |
76.2 |
60. 1 |
|
|
No. 2, SE . |
200 |
78.2 |
64.1 |
|
No. 3, SE., . |
325 |
74.6 |
58.8 |
|
No. 4, SE . |
525 |
74.2 |
57.7 |
|
No. 5, SE . |
725 |
75.9 |
60.8 |
|
Mount Airy: |
|||
|
No. 1, base station, elevation 1,340 . |
85. 1 |
65.0 62.7 |
|
|
No. 2, W . |
160 |
85.1 |
|
|
No. 3, E . |
160 |
83.2 |
63.1 |
|
No. 4, summit . |
360 |
83.6 |
62.8 |
|
Transon: |
|||
|
No. 1, base station, elevation 2,970 . |
77.6 |
58.3 55.6 |
|
|
No. 2, W . |
150 |
75.6 |
|
|
No. 3, W . |
300 |
77.2 |
55.8 |
|
No. 4, summit . |
450 |
74.4 |
55.3 |
|
Tryon: |
|||
|
No. 1, base station, elevation 950 . |
87.5 89.0 |
72.0 71.6 |
|
|
No. 2, SE . |
380 |
||
|
No. 3, SE . |
570 |
83.4 |
69.2 |
|
No. 4, SE . |
1,100 |
81.5 |
68.3 |
|
Wilkesboro: |
|||
|
No. 1, base station, elevation 1,240 . |
87. 1 |
67.5 66.2 |
|
|
No. 2, N . |
150 |
85.8 |
|
|
No. 3, N . |
350 |
83.9 |
65.7 |
|
No. 4, W . |
430 |
83.2 |
64.8 |
25
THERMAL BELTS AND FRUIT GROWING IN NORTH CAROLINA.
Table lb. Average differences between the maximum temperatures at the base station and those higher up on the three long slopes of Altapass, Ellijay,
and Gorge on selected days of cloudy weather in 1915.
|
ALTAPASS. |
Feet. |
Difference. |
|
No. 1, base station . |
||
|
No. 2, SE. slope . |
250 |
-0.7 |
|
No. 3, SE. slope . |
500 |
—1.5 |
|
No. 4, SE. slope . |
750 |
-2.1 |
|
No. 5, summit . Average, 1° for each 312 feet. |
1,000 |
-3.2 |
|
ELLIJAY. |
Feet. |
Difference. |
GORGE. |
Feet. |
Difference. |
|
No. 1, base station . |
|||||
|
No. 2, N. slope . No. 3, N. slope . No. 4, N. slope . No. 5, summit . Average, 1° for each 326 feet. |
310 620 1,240 1,760 |
-0.7 -2.1 -3.7 -5.4 |
No. 2, NE. slope . No. 3, S. slope . No. 4, W. slope . No. 6, summit . Average, 1° for each 347 feet. |
290 615 840 1,040 |
-0.7 -1.8 -2.4 -3.0 |
Table lc. — Monthly and annual average maximum temperatures on six long slopes and rate of decrease with elevation, 1913-1916.
[The slopes selected for this comparison have a difference in elevation 1,000 feet or more between base and summit stations. The differences in temperature between the base and
summit stations are given, as well as the difference in feet, for each degree difference in temperature.]
|
Slopes and stations. |
Elevation (feet).1 |
Month. |
|||||||||||||
|
Base. |
Summit. |
Janu¬ ary. |
Febru¬ ary. |
March. |
April. |
May. |
June. |
July. |
Au¬ gust. |
Septem¬ ber. |
Octo¬ ber. |
Novem¬ ber. |
Decem¬ ber. |
An¬ nual. |
|
|
Altapass, No. 1 . |
2,230 |
2 47.4 |
2 47. 3 |
2 50.7 |
2 65. 7 |
75.0 |
79.3 |
82.0 |
81.2 |
74.9 |
68.2 |
58.6 |
46.8 |
64.8 |
|
|
Altapass^ No. 5 . |
1,000 |
2 43. 1 |
2 42. 7 |
2 46.6 |
2 61.5 |
70.8 |
75.3 |
77.7 |
76.9 |
71.2 |
63.8 |
54.6 |
43.0 |
60.6 |
|
|
Difference . |
—4.3 |
-4.6 |
—4. 1 |
—4.2 |
-4.2 |
-4.0 |
-4.3 |
-4.3 |
-3.7 |
-4. 4 |
-4.0 |
-3.8 |
-4.2 |
||
|
Feet for 1“ difference . |
233 |
217 |
244 |
238 |
238 |
250 |
233 |
233 |
270 |
227 |
250 |
263 |
238 |
||
|
Cane River, No. 1 . |
2,650 |
2 47.9 |
2 46.0 |
2 48.5 |
63.6 |
74.1 |
78.5 |
81.3 |
80.7 |
75.1 |
66.9 |
57.2 |
45.7 |
63.8 |
|
|
Cane Riveri No.4 . |
1,100 |
2 44. 1 |
2 42.9 |
2 46. 1 |
62.6 |
77.2 |
79.0 |
77.4 |
70.7 |
62.8 |
54.4 |
42.9 |
61.2 |
||
|
Difference . |
—3.8 |
—3.1 |
—2.4 |
-1.0 |
+0.5 |
-1.3 |
-2.3 |
-3.3 |
-4.4 |
-4. 1 |
-2.8 |
-2.8 |
-2.6 |
||
|
Feet for 1° difference 4 . |
289 |
355 |
458 |
1,100 |
2,200 |
846 |
478 |
333 |
250 |
268 |
393 |
393 |
423 |
||
|
Ellijay, No. 1 . |
2, 240 |
* 51. 4 |
>51.0 |
>53.6 |
68.1 |
78.1 |
81.8 |
83.8 |
83.1 |
78.2 |
70.3 |
61.3 |
49.8 |
67.5 |
|
|
Ellijay’ No. 5 . |
1,760 |
s 45.8 |
» 46.0 |
>48.2 |
>63.0 |
> 72.7 |
> 75. 3 |
> 77. 0 |
>76.8 |
>72.1 |
> 64.4 |
> 55.0 |
>44.1 |
61.7 |
|
|
-5.6 |
-5.0 |
-5.4 |
-5.1 |
-5.4 |
-6.5 |
-6.8 |
-6.3 |
-6.1 |
-5.9 |
-6.3 |
-5.7 |
-5.8 |
|||
|
Feet for 1 0 difference . |
314 |
352 |
326 |
345 |
326 |
271 |
259 |
279 |
2S9 |
298 |
279 |
309 |
303 |
||
|
Globe, No. 1 . |
1,625 |
50.5 |
50.0 |
54.8 |
67.9 |
78.2 |
82.2 |
84.5 |
82.8 |
77.1 |
70.4 |
60.8 |
48.4 |
67.4 |
|
|
Globe, No. 3 . |
1,000 |
48.0 |
48.2 |
53.1 |
67.3 |
77.4 |
80.1 |
82.1 |
80.4 |
74.2 |
67.3 |
58. 4 |
45. 8 |
65.2 |
|
|
-2.5 |
—1.8 |
—1.7 |
-0.6 |
-0.8 |
-2.1 |
-2.4 |
-2.4 |
-2.9 |
-3. 1 |
-2.4 |
-2.6 |
-2.2 |
|||
|
400 |
556 |
588 |
1,667 |
1,250 |
476 |
417 |
417 |
345 |
323 |
417 |
385 |
455 |
|||
|
1,400 |
50.0 |
50.5 |
56.3 |
69.7 |
SO. 3 |
83.9 |
86.3 |
84.0 |
77.8 |
70.9 |
60.8 |
47.4 |
68.2 |
||
|
1,040 |
48.0 |
47.9 |
53.1 |
67.0 |
76.8 |
80.1 |
82.2 |
80.4 |
73.7 |
66. 4 |
58.4 |
45.4 |
65.0 |
||
|
-2.0 |
-2.6 |
-3.2 |
-2.7 |
-3.5 |
-3.8 |
-4.1 |
-3.6 |
-4.1 |
-4.5 |
-2.4 |
-2.0 |
-3.2 |
|||
|
520 |
400 |
325 |
385 |
297 |
274 |
254 |
289 |
254 |
231 |
433 |
520 |
325 |
|||
|
950 |
54.6 |
54.3 |
59.2 |
71.7 |
81.4 |
86.2 |
88.6 |
86.7 |
80.9 |
74.0 |
63.8 |
51.8 |
71.1 |
||
|
Tryon^ No. 4 . |
1,100 |
51.0 |
50.7 |
55.4 |
68.0 |
77.1 |
81.4 |
84.2 |
82.9 |
77.0 |
70.4 |
61.1 |
48.5 |
67.3 |
|
|
-3.6 |
-3.6 |
-3.8 |
-3.7 |
-4.3 |
-4.8 |
-4.4 |
-3.8 |
-3.9 |
-3.6 |
-2.7 |
-3.3 |
-3.8 |
|||
|
Feet for 1° difference . |
306 |
306 |
289 |
297 |
256 |
229 |
250 |
289 |
282 |
306 |
407 |
333 |
289 |
1 Base station above sea level; summit above base.
> 1913 missing.
3 jqj3 siid 1914 missing
< The datum “Feet for 1° difference” obviously fails of any physical significance when the temperature differences between slope stations are quite small .—Ed.
Table Id. — Monthly and annual average maximum temperatures at the two stations having the highest and lowest elevations, respectively , ^showing the
rate of decrease with elevation, 1913-1916.
|
Stations. |
Eleva¬ tion (feet). |
Janu¬ ary. |
Febru¬ ary. |
March. |
April. |
May. |
June. |
July. |
Au¬ gust. |
Septem¬ ber. |
Octo¬ ber. |
Novem¬ ber. |
Decem¬ ber. |
An¬ nual. |
|
Tryon, No. 1 . Highlands, No. 5 . Number of feet for 1° difference . |
950 4,075 |
54.6 42.7 -11.9 263 |
54.3 41.9 -12.4 252 |
59.2 43.6 -15.6 200 |
71.7 60.4 -11.3 277 |
81.4 70.8 -10.6 295 |
86.2 74.4 -11.8 265 |
88.6 76.5 -12.1 258 |
86.7 75.4 -11.3 277 |
80.9 69.2 -11.7 267 |
74.0 62.2 -11.8 265 |
63.8 54.6 -9.2 340 |
51.8 43.5 -8.3 377 |
71.1 59.6 -11.5 272 |
Average monthly and annual maximum temperature. — A discussion of Table 1, which latter contains the record of the average maximum temperatures at the respective stations, will now follow. The differences between the readings at the base station and those at higher levels in each group can be had by simple inspection. This discussion will also include a study of the maximum temperature during selected periods of clear weather shown in T&bl© In. Th© lnttor tnbl© hns b©©n pr©pnr©d in order that the reasons for the variations during sun¬ shiny weather may be seen and understood.
On account of the shortness of the periods included in Table la, and the great latitude allowed the observers in reading the temperatures to whole degrees, individual
comparisons between the respective stations on the slopes do not always show the uniformity expected. Longer periods, if such were available, would be more satisfactory, as the inequalities would then be smoothed out, or, at least, questionable or unusual values would not stand out so prominently as in a short period.
Since the position of the sun relative to the various slopes, has an important bearing on maximum tempera¬ ture, two clear periods have been selected in Table la, and are presented, one in May, 1914, when the sun is high in the heavens, and the other in November, 1914, when its meridian altitude is low.
Before going into the discussion of the individual tables in detail it might be well first to understand the
26
SUPPLEMENT NO. 19.
reasons for the differing amount of insolation received during sunshiny weather on unit areas of slopes of varying inclination and direction, as illustrated by figure 42.
It is quite apparent from a glance at that graph that practically equal insolation is received during the month of June on both north and south facing slopes, as shown by the areas A, B, and D, the degree of inclination of the slope at this season, when the sun is high in the heavens, being a negligible factor.
However, it may also readily be seen that there is a considerable difference in the insolation on a slope according as it faces north or south during the month of December, when the meridian altitude of the sun is low, as represented by the areas C, E, and A. This is because the same amount of insolation is spread out over much greater area on a north-facing slope than on one with a southerly exposure. Likewise, the intensity of the inso¬ lation received on a north-facing slope during the winter
In Table la there is shown to be a somewhat greater decrease in maximum temperature with elevation during clear weather than appears in the general average in Table 1 embracing all weather conditions, and this is what should be expected, as the vapor pressure is usually less during clear weather. Moreover, Altapass is a regular slope and the exposures of the various stations are quite uniform. There is a certain harmony between the variations during the two clear periods, especially between the two lower stations and that at the summit.
Asheville (Table 1). — During all the months of the ear the maxima at station No. 3 average lowest ecause of its location on the northerly slope close to heavy timber to the south, west, and east, which permits very little sunshine in the vicinity of the shelter and keeps it in a heavy shade. As the slope is rather steep northerly, the effective rays of the sun are at a minimum in the winter, as shown in Figure 42.
months will vary with the degree of inclination, as shown by areas C and E, the gentler the slope the more con¬ centrated the insolation. We find, then, higher maxima during the colder months on a southerly slope than on a northerly one simply because the sun’s rays on a south¬ facing slope are more direct and therefore more effective.
Average Maxima on Individual Slopes; Also Maxima During Sunshiny Periods — Altapass (Table 1). — There is apparently little seasonal change in the differences between the maxima at the five stations on this long southeasterly slope, the differences for the various months being remarkably uniform throughout the year. The maxima at station No. 1 average the highest during all months, and the readings at the sum¬ mit station, No. 5, 1,000 feet above, the lowest. The slight variation in these differences from month to month is due to change in shade from near-by timber and vegetation. The average difference for the four-year period between No. 1 and No. 5 is 4.2°, or a decrease of 1° for each 238 feet. As this is a southeast slope, it has considerable sunshine, especially in the morning.
The maxima average highest at station Nos. 1 and 3a, the readings being slightly lower at No. 3a than at No. 1 in the summer months and slightly higher in early spring and late fall months. No. 3a is on a southerly slope, but the timber during the growing season screens the sun to some extent. On the other hand, the sun’s rays are more direct on this southerly slope at No. 3a during the winter, resulting then in a higher maximum on sunshiny days than at No. 1.
As might be expected, the maxima at station No. 2a on the south slope average higher than at No. 2 on the opposite northerly slope, taking the year as a whole, but the excess is gained wholly during the fall and winter months, while a small negative difference exists during the late spring and early summer months (see table on page 23). The reason for this apparent anomaly is immediately evident upon consideration of the profile of the valley (fig. 17) and the varying meridian altitude of the sun from December to June. When the sun reaches its lowest meridian altitude in December, 31° in the latitude of the Carolina mountain region, the
THERMAL BELTS AND ERUIT GROWING IN NORTH CAROLINA.
27
south-facing slope at station No. 2a receives about twice as much insolation over a given area as No. 2. But after the vernal equinox, as the sun rises higher and higher, this difference in the amount of heat received becomes such a negligible quantity that it may be dis¬ regarded entirely, and it is found that the maximum temperatures are then practically the same at both stations. In June, with the sun’s rays from a meridian altitude of 78°, the insolation on both slopes is about equal in amount, but at No. 2a, where the slope is steep and faces a large area of free air, the unstable equili¬ brium of the surface air is rapidly relieved by interchange.
Another reason for the relatively high maximum during the spring and summer months at No. 2 on the north slope is the fact that there is considerable vegeta¬ tion surrounding the station which serves to trap the heated air while the location on the north facing slope at No. 2a is almost bare of vegetation.
Four-year average maxima, Asheville, Nos. 2 and 2a and 3 and 3a, including direction of slope ana elevation above the base.
|
January. |
February. |
March. |
April. |
May. |
June. |
July. |
August. |
September. |
October. |
N ovember. |
December. |
j Annual. |
|
|
No. 2, N., 155 feet . |
49.4 |
46.7 |
51.2 |
64.0 |
74.8 |
78.8 |
81.1 |
80.2 |
74.8 |
66.1 |
56.9 |
46.0 |
64.2 |
|
No. 2a, S., 155 |
50.1 |
47.7 |
51.5 |
63.9 |
74.0 |
78.2 |
80.4 |
80.2 |
75.3 |
67.2 |
58.2 |
47.3 |
64.5 |
|
Difference . |
+0.7 |
+1.0 |
+0.3 |
-0.1 |
-0.8 |
-0.6 |
-0.7 |
0.0 |
+0.5 |
+ 1.1 |
+ 1.3 |
+ 1.3 |
+0.3 |
|
No. 3, N., 380 |
47.0 |
44.9 |
49. 61 63.0 |
72.8 |
75.9 |
78.0 |
76.8 |
70.4 |
62.4 |
53.8 |
43.6 |
61.5 |
|
|
No. 3a, S., 380 |
51.0 |
48.8 |
52.9 66.3 75.6 |
79.2 |
81.2 |
80.3 |
74.8 |
67.8 |
60.6 |
48. 3 |
05. 0 |
||
|
feet . Difference . |
+4.0 |
+3.9 |
+3.3|+3. 3+2.8 |
+3.3 |
+3.2 |
+3.5 |
+4.4 |
+5.4 |
+6. 8+4.7 |
+4.1 |
From an examination of this table it is evident that the maxima at No. 3 on the northerly slope are lower than those at No. 3a with a south exposure during all months of the year, the greatest difference, 6.S°, occurring m November and the least difference, 2.8 , in May. Duimg June, when the meridian altitude of the sun is the highest, practically equal insolation prevails on these two lacing slopes (see fig. 42) . However, as stated previously, there is a large amount of shade at No. 3 as compared with the conditions in the vicinity of No. 3a, and this effectually screens the sun’s rays from the former, especially m the the middle of the day, so that the temperature there is prevented from reaching as high a point as at No. 3a In December, with the sun at a low meridian altitude, the question of shade, although still a factor, is not so impor¬ tant as the amount of effective insolation received at these two points. Owing to its position on the northeriy slope and timber to the east and west No. 3 at this time of the year is cut off from any rays of the sun, while No. 3a on the opposite slope receives more effective insolation m comparison with that received at No. 3 than it did 111 June.
For the same reason outlined on a previous page m the comparison between the maxima at No. 2 and No. 2a, the months in which the least and greatest differences occur between Nos. 3 and 3a are May and November, iespec- tively instead of June and December, as would be ex¬ pected were the angle of the sun s rays the only factoi. P Figure 43 illustrates the effect of shade m reducing the
mirlnicrht October 30 to noon November 1, 1J13, tne maximum temperature on the southerly slope was each dLv macticallv 13° higher than on the slope opposite. tVe fig£e are also shown the curves of temperature
30442 — 23 - 3
for the same period for the stations Nos. 2 and 2a on these slopes, but here we have no contrast of sunshine and shade, as at the upper stations, but the effect only of northerly and southerly inclination and varying amounts of vegetation. The maxima on the southerly slope at No. 2a rise to a higher point than at No. 2, but the differ¬ ence is only 2° or 3°. In the warmer months of the year, when the sun is more nearly overhead, there is no appre¬ ciable difference between these two stations on days of sunshine.
In the comparison in Table la, the variation in maxi¬ mum temperature at the two stations on the northerly slope, as compared with those at the base and on the southerly slope during the selected periods of clear weather 'in May and November, is quite marked, for reasons similar to those already stated.
Blantyre (Table 1). — Disregarding the summit station, the maximum temperature on this slope decreases uni¬ formly with elevation. The average difference between the summit and the base is very slight, and m some months the average at the summit is higher. This is due doubtless to the fact that there is more effective 'insola¬ tion and denser vegetation at the summit station No. 4 than at No. 1, which is really on a small bench on a o-radual northerly slope, a slight distance above the valley floor. As there is no month in which the average difference between these two stations approaches the normal rate, there must be a factor or factors working durino- the entire year to prevent the temperature at No. l°from reaching higher maxima. The forest growth above and to the south of No. 1 shades this station during much of the time; in the spring and summer on account of the foliage on the trees, and in the fall, even, because the trees, notwithstanding the diminished foliage, otter obstruction sufficient to modify considerably the Gleet of the sun’s heat, although the condition of shade at this point is far from being as pronounced as at station No. 3, Asheville. In the winter the low altitude of the sun becomes an additional factor, while m the summer the excessive cloudiness in the early afternoon aids m cutting down the difference in the maxima between Nos. 1 and 4.
The average difference between the maxima at Nos. 1 and 2 is 0.9° for an ascent of 300 feet, and this is about
what should be expected. .
Station No. 3 has a lower average maximum than any other of the Blantyre stations during the whole year, because of the fact that the slope is northerly and steep and is ineffectively heated by the sun s rays The differ¬ ences between Nos. 1 and 4 and between 3 and 4 are
28
SUPPLEMENT NO. 19.
abnormal. As No. 4 is located on the summit and receives more effective insolation, as previously stated, the maxima at that station are rather high, and this is the case especially in the fall, when the number of clear days is the greatest.
During the clear period in May, as shown by Table la, station No. 2 has an average of 1.1° higher than No. 1, and this is largely because the former is located in a sag or gully where tne warm air is trapped by the near-by vegetal growth, whereas No. 1 is on a flat bench with but little vegetation in the vicinity, besides being in the shade much of the time, as stated above. This excess of 1.1° at No. 2 over No. 1 is in marked contrast with the four-year average deficiency of 0.9° as shown in Table I, and this is because the latter average includes both clear and cloudy days. No 4 also is Iff "her, while No. 3 on the northwest slope has naturally the lowest maximum in the entire group.
During the November period (Table la) station No. 2 shows a more nearly normal rate of decrease as compared with station No. 1, as in this month the vegetation in the vicinity of No. 2 is not a factor. Station No. 3 shows an an increase in the difference between it and No. 1 in November as compared with May, and this is no doubt due to the more effective insolation at No. 1 than at No. 3 during this month, when the meridian altitude of the sun is low, while the effect of shade at No. 1 in November as compared with the station No. 4 on the summit is responsible for the variation in the difference shown in Table la between these two locations.
Blowing Rock (Table 1). — In comparing the maximum temperatures at Blowing Rock, it should be understood that there are two groups of stations on different slopes about one-half mile apart, stations Nos. 1 and 2 being located in the China orchard and Nos. 3, 4, and 5 in the Flat Top orchard.
The highest maxima occur at No. 1, although there is very little difference between this station and No. 2. No. 1 is by no means a base station, as both it and No. 2 are on a rather steep southerly slope in the China orchard. No. 2 receives more effective insolation than No. 1, espe¬ cially in the winter; hence this slight average difference between the stations, 0.3°, although the difference in elevation is 450 feet. The maxima m the China orchard are uniformly higher than those recorded at stations Nos. 3, 4, and 5 in the Flat Top orchard because of the difference in local exposure. Nos. 1 and 2 are situated on a steep narrow slope with high inclosing sides, which tend to prevent a free circulation of air, and thus aid in producing relatively high maxima, while Nos. 3, 4, and 5 have a freer exposure, as they are located on the slope of a huge amphitheater-shaped basin with an opening to the southeast. (See fig. 30.)
During the period of clear weather in May (see Table la) the difference between the values at Nos. 1 and 2, — 1.8°, is about what should be expected, while there is a difference of only +0.1° in the November period. This variation is undoubtedly due to the fact that in the winter there is more effective insolation at No. 2 than at No. 1, while in the summertime the normal rate of decrease be¬ tween the two points prevails, as the amount of insolation received at Nos. 1 and 2 is practically equal. For the same reason there is a seasonal variation in the rate of decrease between Nos. 2 and 3 in that No. 2 averages 0.9° higher in the May period and 2.3° higher in the November period.
Bryson (Table 1). — The differences between the max¬ ima, at Bryson do not vary materially for the entire period, but there is a remarkable seasonal variation noted
between Nos. 1 and 3, the base and the summit stations. Beginning with February, the temperature at No. 3 exceeds that at No. 1, culminating in the month of April with a four-year average excess of 3.7°. With the advance of the season, the difference gradually becomes less and less until July, when it becomes a deficiency which increases to an average of 2° in December. This change is quite uniform throughout each of the four years of record and may be due to the rapid growth of vegetation in the vicinity of No. 3 in the early spring, although tlxis could not be considered a factor as early as February. However, the excess in maximum tempera¬ ture at No. 3 does not begin until toward the close of that month, the vegetation there doubtless reaching its maximum density in May. The peculiar situation at No. 3 is probably due to some extent at least to the surrounding vegetation and timber in the vicinity, which trap the warm air. The condition is purely local, and the temperature oscillates considerably on sunshiny days during the months in which the excess is noted, especially in the spring.
The difference in height between the summit and the base being 570 feet, the average decrease in temperature of 2°, as noted in December, does not differ much from the normal rate in strong contrast with the excess of 3.7°, noted in April. The average excess at the summit in April, 1914, amounted to 4.6°, while the average deficiency in September, 1916, was 3.9°.
Of course, where sunshine is a principal factor in governing a variation, the monthly average differences should depend upon the relative frequency of sunshiny days, the greater the amount of sunshine the more marked the excess or deficiency as the case may be, while in months with an excess of cloudiness the differences in the maximum temperature should depend almost entirely upon elevation. For instance, in July, 1916, a cloudy month, the average deficiency at No. 3 as compared with No. 1 was 1.8°, while in July, 1913, a sunshiny month, the average excess at the summit station was 0.3°.
The variation in maximum temperature between the the northerly and southerly slopes at both Asheville and Bryson is consistent in the various months of the year, as shown by the table below, in that the excess on the southerly slope is greatest at both places during the winter season, when the sun is farthest south, with the most insolation on a south-facing exposure. The excess on the northerly slope is greatest at Asheville from May to July, inclusive, and at Bryson from July to September, but at Bryson the differences in the summer are very slight. This table indicates the mean differences by months for stations No. 2 and No. 2a at both Asheville and Bryson. The grades of these slopes are not the same, so that, of course, the comparison will serve only in a general way.
Four-year average maxima, Asheville and Bryson, Nos. 2 and 2a, including direction of slope and elevation above the base.
|
January. |
February. |
March. |
April. |
May. |
June. |
July. |
August. |
September. |
October. |
November. |
December. |
Annual. |
|
|
Asheville: 2, N., 155 feet . |
49.4 |
46.7 |
51.2 |
64.0 |
74.8 |
78.8 |
81.1 |
80.2 |
74.8 |
66.1 |
56.9 |
46.0 |
64.2 |
|
2a, S., 155 feet . |
50.1 |
47.7 |
51.5 |
63.9 |
74.0 |
78.2 |
80.4 |
80.2 |
75.3 |
67.2 |
58.2 |
47.3 |
64.5 |
|
Difference. . |
+0.7 |
+ 1.0 |
+0.3 |
-0.1 |
-0.8 |
-0.6 |
-0.7 |
0.0 |
+0.5 |
+1.1 |
+1.3 |
+ 1.3 |
+0.3 |
|
Bryson: 2, N., 385 feet . |
50.6 |
51.1 |
54.1 |
68.9 |
79.4 |
82.8 |
84.8 |
84.2 |
79.2 |
70.4 |
59.8 |
46.4 |
67.6 |
|
2a. S., 385 feet . |
52.3 |
52.2 |
55.1 |
69.8 |
79.7 |
82.9 |
84.7 |
83.8 |
79.0 |
71.4 |
61.6 |
48.2 |
68.4 |
|
Difference. . |
+ 1.7 |
+1.1 |
+ 1.0 |
+0.9 |
+0.3 |
+0.1 |
-0.1 |
-0.4 |
-0.2 +1.0 |
+1.8 |
+1. 8 |
+0.8 |
THERMAL BELTS AND FRUIT GROWING IN NORTH CAROLINA.
Cane River (Table 1). — The maxima do not decrease here with elevation through the various months of the year with any regularity. The readings at station No. 3, 400 feet above the base, are unusually low, and those at No. 4 relatively high; in fact, for the four-year period No. 4 averages 0.4° higher than at No. 3, which is 700 feet lower down.
No. 3, which is in a cove-like depression on a north slope, with Rocky Knob towering above to the south and timber in most directions except southeast, is not only cut off from sunshine during much of the morning and afternoon, but the slanting rays of the sun on the steep slope are ineffective in raising the surface tempera¬ ture. This condition, of course, is most marked during the sun’s lowest meridian altitude, and the difference in insolation as reflected in the daytime temperatures at Nos. 3 and 4 is well shown in figure 44.
A seasonal variation is noted between No. 3 and No. 1 in that the maximum at No. 3 is much lower than that at No. 1 in the colder months of the year, and we would expect on this account to find the greatest average monthly difference between the maxima at No. 1 and No. 3 in December, but this actually occurs in October and November, because of the large number of sunshiny days in those months. During the month of October, 1914, the average difference between the maxima at Nos. 1 and 3 on 8 cloudy days was 1.7°, while on 17 clear days the average difference was 7.6°. The greatest difference on any cloudy day was 5°, while on one clear day the difference was 13° and on a majority of the 17 days the differences were 8° or more.
Kow, taking the month of May, 1914, a month unlike October in that the altitude of the sun is then higher, when its rays reach into the cove at No. 3, thus producing more equal insolation at Nos. 1 and 3 than during October when the altitude of the sun is lower, we find an average difference of 1.7° between Nos. 1 and 3 for 7 cloudy days, exactly the same as during a period of cloudy weather in October, 1914; while on 18 clear days in May the average difference is only 1.5°, compared with an average differ¬ ence of 7.6° in a period of clear weather in October, 1914. On 1 cloudy day in May, 1914, the extreme difference of 5° was noted, while on no one of the 18 clear days was there a difference greater than 3°.
Therefore, in the summer time, when the sun is highest and the rays strike directly down into the cove at No. 3, the differences between the maxim at Nos. 1 and 3 are small as compared with those in the colder months of the year. If June and December were as clear as May and October, the least and greatest ranges between the differences at Nos. 1 and 3 would be found in the former months, but the latter months are taken simply because of the greater number of sunshiny days.
The average decrease, 2.6°, in maximum temperature for the four-year period from No. 1 to summit station No. 4 for an elevation of 1,100 feet is at the rate of 1° for 423 feet. No. 4 is located on a knob with dense timber below on all surrounding slopes, except on the east side, and a vast amount of heated air is trapped in the upper portion of the timber, and this heat, together with that radiated from the surface of the foliage, is felt on the knob. There is, moreover, a clearing around the shelter, permitting free exposure to sunshine at all times, although small brush covers the ground.
In Figure 44 are temperature curves representing Nos. 1, 3, and 4, Cane River, for the two days January 4-5, 1916, which show the great excess in day temperature during sunshine at Nos. 1 and 4 as compared with that at No. 3. On the 4th, a clear, calm day, the maximum
at No. 3 was 12° lower than that at Nos. 1 and 4, where the maxima were unusually high, being intensified by the existing calm, while on the 5th, a cloudy day, the differences in maxima were not so marked.
Ellijay (Table 1). — The maxima at Ellijay show greater uniformity than perhaps any other group of stations not only in the four-year averages but in the individual months. With an elevation of the summit station above the base of 1,760 feet on this northerly slope there is an average decrease in maximum tempera¬ ture of 5.8°, approximately 1° for each 303 feet. No. 4, at an elevation of 1,240 feet above No. 1, shows the only irregularity, doubtless because of the configuration of the slope and the near-by timber, which shut off the sunshine more than at the other stations, especially in the winter months. Tins slope and that at Altapass are the most regular of all the slopes.
The variation in the maximum temperature during the May clear period (Table la) shows a comparatively lower reading at station No. 3 and a higher one at No. 4 than is indicated by the four-year averages. In this case the readings of all the stations are consistent except that at No. 3, which for some reason is not in harmony with the averages at other stations.
Fig. 44. — Thermograph traces, January 4-5, 1916, stations Nos. 1, 3, and 4, Cane River.
The Ellijay stations, located as they are on a northerly slope, naturally have lower day temperatures as com¬ pared with the'base during the month of November than in May, and this fact is brought out by the figures in Table la, with the exception of those at station No. 3.
Globe (Table 1).— In this group of three stations the maximum readings do not show a decrease approaching the normal rate. Station No. 3, at an elevation of 1,000 feet above No. 1, has a mean maximum only 2.2° lower than No. 1, approximately 1° for each 455 feet. This slight decrease is doubtless because No. 3, the summit station, being located on an arm of Grandfather Mountain, receives a much greater share of insolation than the base. The maxima at No. 2 on the easterly slope, only 300 feet above the base, averages 1.8° lower than No. 1, this large difference being due to the shutting off of the sun at No. 2 by surrounding timber early in the afternoon, especially in the late tall and winter, as stated in description of Figure 35.
In the comparison in Table la, the effect of sunshine on elevated sections is shown as compared with those lower down.
A marked seasonal variation between the maxima observed at Nos. 2 and 3 is brought out strongly by the figures in Table la. During the period in November
30
SUPPLEMENT NO. 19.
No. 3 averages 3.3° higher than No. 2, located 700 feet below, while in May it averages higher by but 0.1°.
Gorge (Table 1). — At the summit station of Gorge, with an elevation of 1,040 feet above the base, the maxi¬ mum averages 3.2° lower than at the base, approxi¬ mately 1° difference for each 325 feet. The average differences for July, September, and October all exceed 4°, while in January and December the average differ¬ ences are as low as 2°. This variation is due largely to the fact that the sun’s rays are far more effective in the warmer months than in the cold months of December and January at the base of a northeasterly slope on which No. 1 is located as compared with the summit. In the latter months, when the sun’s rays strike this north¬ easterly slope obliquely, the maximum readings at all stations on the slope, including No. 1, more nearly approximate the readings at the summit. This is brought out by the figures in the tables and should be compared with the monthly variation on the southeasterly slope at Altapass, for instance, which shows no such variation in maximum temperature differences at its stations in the different months of the year. In fact, at Altapass the maximum temperature in the summer at the summit averages lower than the base station by the same amount as during the winter. The average difference of 4.2° for the four years at Altapass for a difference in elevation of 1,000 feet is even somewhat exceeded in the winter months, January showing a difference of 4.3° and Febru¬ ary, 4.6°, while at Gorge, for a difference in elevation of 1,040 feet between the base and the summit, the average four-year difference is 3.2°, but the January and February months have differences of only 2° and 2.6°, respectively. These figures indicate strongly the effect of the direction of the slope on the maximum temperature as modified by the season, which fact is also brought out prominently in the comparisons between the northerly and southerly slope stations at Asheville and Bryson. (See the dis¬ cussion on those stations.)
The rates of decrease in maximum temperature, 1.1° between Nos. 1 and 2 at Gorge for a difference in elevation of 290 feet and 2.6° between Nos. 1 and 3 for a difference in elevation of 615 feet, are somewhat above the average, but this is not strange, especially as compared with the situation at No. 5, because Nos. 2 and 3 are shut off from sunshine during a considerable portion of the day. The rate, however, at No. 4 shows a smaller value, 2.8° for 840 feet, or 1° for 300 feet. But this statement needs some qualification. No. 4 was located during 1913 and 1914 on a north slope at an elevation of 840 feet above the base, and during 1915 and 1916, on a northeast slope at the same elevation. The maxima were much higher at the first location than at the second as compared with the base station, the average two-year difference between the old No. 4 and No. 1 and between the new No. 4 and No. 1 being 1.8° and 3.8°, respectively. There was a better ex¬ posure to insolation at the old location, as the shelter was located on a small ridge with downward slopes on either side to west and east, in the midst of surrounding vegeta¬ tion such as is likely to be found in any neglected apple orchard; and on sunshiny days the radiation of heat from this vegetation was relatively large. The maxima in 1915 and 1916, however, were low as compared with those at the old location in 1913 and 1914, as the station did not have such a free exposure to sunshine in the later period and there was not as much vegetation sur¬ rounding the shelter. Fig. 36 shows the locations of the old and the new No. 4 stations, respectively.
The comparison in Table la for the clear periods will serve to bring out more prominently the variation be¬
cause of sunshine. During the May period the maxima were really lower at all the stations above the base than we should expect, the low reading at No. 3 in the cove at an elevation of 615 feet above the base being the most pronounced.
As a rule during November the maxima on the slope are not so low as compared with the base as in May, and this is probably because of the greater amount of sun¬ shine during months when the foliage has fallen from the trees. This is clearly the case at station No. 4, which, although located on a northerly slope in 1914, has at the same time a free east and west exposure, the location of the shelter being on a ridge or hogback.
Hendersonville (Table 1). — The maximum at the sum¬ mit averages 3.2° lower than at the base station for a difference in elevation of 750 feet, a rate of 1° for each 234 feet, and this does not seem to be due so much to the fact that No. 4 is low as it is that No. 1 is rather high. The difference is quite marked between Nos. 1 and 2, 2.1° for 450 feet, but the decrease between Nos. 2, 3, and 4 is smaller and quite regular. The maximum at No. 1 reaches a high point on days of sunshine, as it is located in a pocket surrounded by trees on all sides except to the southeast, thus trapping the air and preventing free circulation.
The decrease in maximum temperature with elevation during the clear period in May, 1914, as shown by Table la, is somewhat greater between Nos. 3 and 4 than the four-year average decrease and less between stations Nos. 2 and 1, and this variation, as well as that between the May and November clear periods, is due to the effect of wind direction. During the week in May the weather was characterized by light variable winds, mostly south¬ erly with frequent calms, while in the period in the fall the winds were light to moderate northwesterly. The small average difference between the maxima at Nos. 1 and 2 in May is accounted for by the fact that during this period with southerly winds No. 2, being located in a basin protected by a ridge to the south, has relatively high maxima. In fact, high temperatures are observed at this location during periods of calm also, as there is no interchange of air between the saucer-shaped depression where No. 2 is situated and the free air outside. In November, with light to moderate northwest winds, a circulation is produced at No. 2 as this station is not then rotected from such winds, which condition prevents igh maxima as compared with No. 1, where the ques¬ tion of wind direction and velocity is not a factor. For this same reason station No. 3 averages 1.4° lower than No. 2 in May and 0.1° higher in November. It is there¬ fore apparent that No. 2 has relatively high maxima in the spring and relatively low maxima in November, during both periods the wind direction not being a factor at either No. 1 or No. 3. In other words, Nos. 1 and 3 are what might be termed “constants” and No. 2 the “ variable.”
This effect in wind direction is strikingly shown by the daily maximum readings at Hendersonville on three suc¬ cessive days in November, 1914, and the following table will serve to illustrate the differences in maximum tem¬ peratures under varying wind directions and velocities.
|
Date. |
Maximum tempera¬ tures. |
Wind direction and velocity. |
||
|
No. 1. |
No. 2. |
No. 3. |
||
|
Nov. 23, 1914 . |
53 |
46 |
47 |
Light northwest winds. |
|
Nov. 24, 1914 . |
48 |
47 |
48 |
Do. |
|
Nov. 25, 1914 . |
61 |
56 |
57 |
Do. |
THERMAL BELTS AND FRUIT
Highlands (Table 1).— Stations Nos. 1 and 2- are in the oatulah orchard under conditions much unlike those ob¬ taining m the Waldheim orchard 2 miles distant, where 3> and 5 are located. While the maxima at No. 2, feet an oye No. 1, should, because of elevation, average slightly lower, the four-year mean is 0.6° higher, doubt¬ less because of the radiation of heat from Mount Satulah the immense rock which stands to the north and northeast immediately above. This temperature excess at No. 2 over No. 1 is greatest in the winter, when the sun is in the south and its rays more directly strike the side of the rock above No. 2. Moreover, No. 2 is located in an orchard in the midst of rather high grass and fruit trees, the headed air being trapped by the surrounding vegetation, while No. 1 is over comparatively bare soil. On many sunshiny days the excess in maximum temperature at No. 2 is large, while during periods of cloudiness and pre¬ cipitation No. 2 averages lower than No. 1.
During the month of December, 1914, when the average maximum temperature at No. 2 exceeded that at No. 'l by 3.5°, the average excess at No. 2 on nine days with sunshine was 5.3°, while on nine days without sunshine the average was 2.6°. On one clear quiet day No. 2 recorded a maximum of 45°, while No. 1 recorded 35°, a large difference, considering the short distance between the two stations. During July, 1916, a month with ex¬ cessive precipitation and much cloudy weather, the the average difference between the maxima at Nos. 1 and 2 was 1.0°, No. 2 in this case averaging lower than No. 1. In July, 1914, a month with little precipitation and much sunshine, No. 2 averaged 1.5° higher than No. 1.
The rate of decrease in maxima between No. 1 in the Satulah orchard and No. 3, the base station in the Wald¬ heim orchard, 1.9° for 325 feet, is greater than the normal rate, doubtless because of the better exposure to insola¬ tion at No. 1 as compared with that at No. 3. However, the variation between Nos. 3 and 4, 0.6° for 200 feet, is ractically normal. But No. 5, 200 feet above No. 4, as actually a higher average maximum than No. 4 by 0.2° for the four-year period. Although both stations are on a slope, the slope is steeper at No. 4 than at No. 5, and therefore the maxima at the latter would more nearly approach those found over level places. No. 4 has thus a freer exposure than No. 5 because of the above fact and also because No. 5 is protected on the west and south by forest growth, which is not found around No. 4. The excess in average maximum temperature at No. 5 over No. 4 is due wholly to the gain made on days of sunshine, the readings being actually lower on cloudy days.
The variation at Highlands during the selected period of sunshine in May shown in Table la is rather irregular, but conforms to the statements in foregoing paragraphs, and the variation in the November perioclis much the same as in May.
Mount Airy (Table 1). — The maxima average lower from the base to the summit, but the range in elevation at Mount Airy, of course, is not great. There are differences of 0.9° and 1.1° between Nos. 1 and 2 on the west slope and between Nos. 1 and 3 on the east slope, respectively. Both slope stations are 160 feet above the base, while the decrease in temperature between Nos. 1 and the summit station, No. 4, for a difference in elevation of 360 feet is 1.6°.
Station No. 1 averages rather high in comparison with the other stations because of its exposure on a broad bench, where there is a large amount of radiating surface. No. 2, on the west slope at an elevation of 160 feet above the base, averages for the four-year period 0.2° higher than No. 3 at the same elevation on the east slope, and it is
GROWING IN NORTH CAROLINA. 31
found to be generally the case that the average maxima on the west side are higher. Moreover, the excess at No. 2 over No. 3 is largely in the warmer season of the year, as shown by the following table, which gives the averages and differences for the four-year period for the two stations:
Four-year average maxima, Mount Airy, Nos. 2 and 3, including direc¬ tion of slope and elevation above the base.
|
January. |
February. |
1 March. |
April. |
May. |
June. |
July. |
August. |
September. |
October. |
November. |
December |
Annual. |
|
|
No. 2, W., 160 feet . No. 3, E., 160 feet . |
48.4 48.8 |
47.2 47.4 |
53.6 53.7 |
67.2 66.8 |
78.1 77.4 |
83.3 82.4 |
85.2 84.8 |
82.4 82.3 |
77.1 77.0 |
68. 8 68.4 |
58.2 58.2 |
45.5 46.2 |
66.3 66. 1 |
|
© 1 |
-0.2 |
-0.1 |
+0.4 |
+0.7 |
+0.9 |
+0.4 |
+0.1 |
+0.1 |
+0.4 |
0. 0-0.7 |
+0.2 |
Plus (+) sign excess and minus (— ) sign deficiency of No. 2 as compared with No. 3.
From a study of this table it is evident that the seasonal variation in maximum temperature between Nos. 2 and 3 is due almost wholly to the varying angle of the sun’s rays from month to month as they fall upon slopes of different direction and grade. Beginning with April and continuing through the summer and into the fall, No. 2 is warmer because at the time of maximum temperature the sun’s rays are more effective at that station than at No. 3 on the east slope, as brought out by the topographi¬ cal map (see fig. 39). In the winter the rays of the sun, although coming from a lower altitude, fall upon No. 3 almost perpendicular, because at that location the ground slopes downward to the south as well as to the east, while at No. 2 the slope is distinctly westward, the insolation therefore reaching the station from the side. This seasonal variation is more strongly shown in Table la, a discussion of which is given in the following paragraphs.
During the sunshiny period in May, 1914 (Table la), No. 2 on the west slope averages exactly the same as the base, while the station on the east slope at the same elevation, 160 feet above the base, averages 1.9° lower than the base, conforming generally to the theory that, during sunshiny weather a west exposure has a higher day temperature than an easterly slope. The summit, station, 200 feet above No. 3, has also a higher tempera¬ ture than this easterly slope station during the period.
The variation in maximum temperature during the clear period in November (Table la) is much the same as in May, with the exception of No. 2 on the west slope, which averages 2.3° lower than No. 1, while there is no difference between these two stations in the spring. Here, again, it is a question of insolation, the sun being low in the south in November and its rays striking No. 2 from the side with small heating effect as compared with their influence on the level surface at No. 1 . The seasonal variation between Nos. 2 and 3 is well shown in this table for the reasons advanced in a preceding paragraph, No. 2 averaging 1.9° higher than No. 3 in May and 0.4° lower in November. Because of the varying effect of insolation at No. 1 and No. 4, there is a variation of 0.7° between the average differences for the two periods, No. 4 being the lower, as would be expected, in both cases.
Transon (Table 1). — There is no regularity in the re¬ lation between the maxima at the Transon stations. No. 2 on the west slope, 150 feet above the base, averages 2.1° lower, or about 1° for 71 feet difference in elevation; yet at No. 3, 150 feet higher up, the average maximum is actually 0.2° higher than at No. 2. On the other hand,
32
SUPPLEMENT NO. 19.
No. 4, on the summit, with an elevation of 450 feet above the base, averages 3.5° lower than the base. Either the readings at Nos. 1 and 3 must be rather high or those at Nos. 2 and 4 rather low for their elevation. As a matter of fact, both of these conditions may be true. No. 1 is in a cove, the country to the east and to the west being rather flat for a mountainous section and with con¬ siderable vegetation around the shelter, while No. 3 has a free exposure toward the west, with ample sunshine. But even here the decrease from the base station up the slope is considerable, 1.9° for 300 feet. So it must be considered that the base station, at least, has relatively high maxima. No. 4, of course, has a free exposure on the summit of a small knob wdth but little vegetal cover, and therefore its maximum temperatures are lower than No. 1, especially on clear days, assuming, of course, that the sunshine at the base station is not cut off materially. On some days the maxima at No. 4 are actually 8° lower than at No. 1. During November, 1914, the average difference for 21 clear days was 4°, with an extreme difference of 8°, while during a period of clear days in May, 1914, the average difference was 3.6°, with an extreme difference of 6°. On cloudy days the differences ranged from 0.6° to 2.3°.
In a comparison of the maxima during the May period of clear weather (Table la) the relations between sta¬ tions Nos. 1, 2, and 4 seem to be about the same as shown by the four-year averages, the differences at these sta¬ tions, as stated above, being rather large considering the slight elevations. Station No. 3, however, on the west slope, has a relatively high maximum during the period of sunshine, as should be expected.
The variation during the clear period in November is somewhat different from that in May, in that station No. 3 averages considerably lower than the base, the difference being 2.5°, while in May there is a decrease of but 0.4°. However, as in the spring period, the averages at all the upper stations, Nos. 2, 3, and 4, are lower than at the base.
Tryon (Table 1). — The decrease in maximum temper¬ ature from the base station, No. 1, to Nos. 2, 3, and 4 is not uniform but most irregular. The slight average difference, only 0.5° between Nos. 1 and 2 for a difference in height of 380 feet, can be accounted for by the large amount of vegetation at No. 2, this causing a relatively high maximum at that point. Moreover, No. 2 is on a rather flat surface on a general southeasterly slope, so that the maximum there approximates closely that at No. 1 in the valley. In fact on sunshiny days the temperature at No. 2 is as high or higher than that at No. 1, while on cloudy days it is often a degree or more lower.
The average maximum at station No. 3, 570 feet above the base, is abnormally low, the average decrease being 3.1°, equivalent to 1° for 184 feet. There is, moreover, an average decrease of 2.6° from No. 2 to No. 3, although the difference in elevation is only 190 feet, amounting to 1° for 73 feet. The No. 2 shelter is located just below the lower edge of a vineyard in a plot of long grass and weeds, while No. 3 is directly above the upper edge in a small orchard where vegetation is rather thin. We should expect more than the usual decrease between Nos. 2 and 3, because No. 2 is the more favorably situated for high day temperatures during periods of sunshine; but the unusual difference of 2.6° on an average seems rather difficult to explain.
The apparent discrepancy might be accounted for possibly by assuming that the thermometer at No. 3 registered 1° too low, but this supposition is hardly
justified, because of the close attention given to the instruments.
In connection with the above, it is interesting to note that the maximum at the summit station in its relation to the base, 1,100 feet below, appears to be normal, as there is a decrease between the two of 3.8°, or 1° for 289 feet. This fact makes the maximum readings at station No. 3 appear even more strange, that station averaging only 0.7° higher than No. 4, although the difference in elevation between Nos. 3 and 4 is 530 feet. In fact, No. 4 conforms so closely to what should be expected for all the months of the year that the record at that point does not require detailed discussion.
The comparison of the selected sunshiny periods (Table la) does not explain the apparent anomaly at station No. 3. The average of the maxima at No. 2 during the period of clear weather in May is 1.5° higher than the base station, but the average at No. 3 is 4.1° lower. In the selected May period No. 4 has a com¬ paratively low maximum, being 6° lower than the base.
In the November clear period (Table la), the varia¬ tion is more regular, as there is a gradual decrease from the base to the summit, the difference being relatively great between stations Nos. 2 and 3, but not nearly so great as during the May period.
WiTkesboro (Table 1). — Station No. 1 is located in a comparatively flat open plot on a bench although not so extensive as that at Mount Airy, but sufRcienctly so to cause relatively high maximum temperatures. More¬ over, No. 2, 150 feet, and No. 3, 350 feet, above the base, are located on northerly slopes, and therefore their maxima are relatively low. No. 4 also has a rather low maximum, with a decrease of 2.4° for an elevation of 430 feet above the base. The markedly super- adiabatic rate of decrease in temperature is undoubtedly due to the character of the exposure of No. 1, which is unduly heated on sunshiny days during the entire year; but the more direct insolation and the retarded air movement over the flat surface, with the increased vegetation during the warmer months of the year, produce relatively higher maximum temperatures than in the autumn, when the effect of vegetation is practically at a minimum. Nos. 2, 3, and 4 are ideal slope stations with open exposure, which in itself would be sufficient reason for the relatively low maximum temperatures at these locations as compared with No. 1 in all months of the year.
During both sunshiny periods, as shown by Table la, the decrease is much greater at Wilkesboro than the four-year averages would indicate. Considering the shortness of the slope, the decrease in maximum tempera¬ ture is greater here than at any other place, there being a decrease of 3.9° for a difference in elevation of 430 feet between No. 1 and No. 4.
Variations in maximum temperature in clear and cloudy weather. — The irregularities in clear weather are due largely to local exposure in the shape of timber and topography, which cut off the sunshine in varying degrees near the time of maximum temperature, and to surrounding vegetation, which allows abnormal local heating of the air. There are a number of instances of this abnormal heating, especially at Highlands No. 2, Asheville No. 3a, Blantyre No. 4, Bryson No. 3, Cane River No. 4, Globe No. 3, Transon No. 1, and Tryon No. 2, as brought out under the discussion of maximum temperature on the individual slopes. Generally speak¬ ing, this factor is most important during the growing season, probably most effective from May to August, when vegetation is densest, and least effective during the
33
THERMAL BELTS AND FRUIT GROWING IN NORTH CAROLINA.
winter. However, the conditions noted during the selected period in May (Table la) are dependent on sun¬ shine at the time of the maximum temperature, but the frequent cloudiness in the afternoon at the time of the maximum temperature during June, July, August, and September minimizes local overheating at these stations, so that the decrease in maximum temperature does not differ greatly from the normal decrease with elevation.
With the approach of clear weather in autumn, the maximum temperature at such stations is again slightly increased, although the decrease in the surrounding vegetation prevents the marked local heating which occurs in April and May. However, it will be noted that the four-year average excess in maximum temperature for November, as shown in Table 1, at the summit stations, Asheville No. 3a and Blantyre No. 4, over those at the bases is about equal to the excess recorded in the spring, but this is not due entirely to the increase in the percentage of sunshine, as is the case at the remaining stations, but rather to other reasons which have been described previously.
Fig. 45. — Average daily maxima during selected period of clear weather in spring; stations grouped according to elevation above sea level.
Naturally, there is greater uniformity in the decrease in temperature with elevation during cloudy weather than during days of sunshine, as then the effect of local overheating is avoided.
The figures in Table lb show the rate of the decrease on selected days of cloudy weather in the year 1915 on the three long slopes having five stations from base to summit, separated from each other more or less uniformly.
The rates of decrease in temperature on these three slopes are fairly uniform at different elevations, and for the slopes as a whole there is a decrease of 1° for each 312 feet at Altapass, each 326 feet at Ellijay, and each 347 feet at Gorge. These rates are all less than the normal rate of decrease in free air — 1° for 300 feet doubtless because of the higher vapor pressuie under
cloudy conditions. , . ,
Figures 45 and 46 furnish a grapmc representation ot the variation in maximum temperature at all the stations in the research during the selected clear periods in spung
and autumn. . .
The high maximum at Tryon No. 2 in autumn (fig. 46) as compared with the others at the same elevation is due to more insolation on this southeast slope and is in con¬ trast with the slight differences in the averages during the spring period (fig. 45). There is also here apparent,
for the same reason, a marked difference between the stations Nos. 2 and 3 at Mount Airy in the spring as compared with the readings in autumn, doubtless because the direction of slope is not so important in the spring.
Other instances bearing upon this point will be found, such as the readings at stations Nos. 2 at Globe and No. 3 at Gorge, and Asheville stations Nos. 3 and 3a. Cane River No. 3, located in a cove on a northerly slope, is also another striking example of difference in insolation between spring and autumn. Then there are the rela¬ tively high readings in the spring at Bryson No. 3 and Cane River No. 4, both summit stations, due to the large amount of vegetation which traps and radiates the heated air near the shelters.
Rates of decrease in monthly and annual average maxi¬ mum temperature on six selected long slopes. — -The figures in Table lc show that for the entire period of four years the rate of decrease in average maximum temperature with elevation on the Altapass, Ellijay, and Gorge slopes was greater than during the cloudy period included in Table lb.
Fig. 46. — Average daily maxima during selected period of clear weather in autumn; stations grouped according to elevation above sea level.
The largest decrease is found at Altapass, with a rate of 1° for each 238 feet. Ellijay is close to the normal rate for free air, with 1° for each 303 feet, and Gorge less than the normal, with 1° for each 325 feet.
The data are included in Table lc also for the three other long slopes, Cane River, Globe, and Tryon.
The rates of decrease at Cane River and Globe, 1° for each 423 feet and 455 feet, respectively, are abnormal because of local conditions previously referred to, while the rate at Tryon is about normal, with 1° for each 289
feet. . .
Monthly and annual average maxima at the two stations having, respectively , the highest and lowest elevations .—A. comparison is made in Table Id for the four-year period between the average maximum temporatures at the lowest and the highest stations employed in the research, Tryon No. 1, 950 feet in elevation, base station, and Highlands No. 5, 4,075 feet in elevation, the summit station. The difference in elevation between these two stations is 3,125 feet, the extreme range employed in
this research. ...
For this difference in elevation there is an average four-year difference in maximum temperature of 1L5. , the greatest average monthly difference being 15.6 in Mar oh and the least 8.3° in December.
34
SUPPLEMENT NO. 19.
The rate of decrease for the entire period between these two stations is 1° for 272 feet. The difference in latitude between Tryon and Highlands is negligible in so far as its effects on temperature are concerned, both being located close to the southern boundary of the State.
MINIMUM TEMPERATURE.
Inversions and norms. — The subject of minimum temperature in mountain sections is much more compli¬ cated than that of maximum. There is usually a certain uniformity in the variation of mean maximum tempera¬ ture, because on most slopes there is an average decrease from the lowest to the highest elevations; but no such regular decrease is found in the averages of minimum temperature. This is because on some nights there is a steady decrease in temperature from the base to the summit, on other nights an increase, and on still other nights an increase to a certain point on the slope and then a decrease farther up. So, in the one instance we have the usual decrease in temperature on account of eleva- ' tion, called here “norm” for the sake of convenience, and in the other two, the variations due to both inversion and norm conditions. There is usually a decrease in minimum temperature from the base to the summit on cloudy or windy nights, while on comparatively clear nights, with little or no wind, an inversion occurs with the lowest temperature in every case at the base. Some¬ times, there is even a combination of the two, norm and inversion, as we shall point out later.
Additional types of inversions. — When reference is I made in meteorological literature to night inversions, it I has been generally understood that they occur only in a | region with high pressure, clear weather, and light wind or calm. It is seldom stated that inversions of con¬ sequence occur under other conditions, but this study in the Carolina mountain region furnishes additional in¬ formation on the subject. True it is that the most marked instances of inversion usually occur under high- pressure conditions, but we find that inversions obtain also in the passing of the high tlnd in the approach of the low. We have in consequence concluded that in¬ versions may be divided into three different types, the Anticyclonic or Ideal Type, the Recovery or Inter¬ mediate Type, and the Cyclonic or Overflow Type.
The Anticyclonic or Ideal Type is of course the one best known, and the best examples of this type occur when the anticyclone persists two or more days.
The Recovery or Intermediate Type is marked by a more rapid movement of anticyclones than in the first- named type, and occurs during the transition from an anticyclone to a cyclone. Inversions of this character are pronounced on only one night, as a rule, but they are sometimes greater than those found under the Anti¬ cyclonic Type. The Recovery Type is usually accom¬ panied by clear weather and light winds and is largely due to the stagnation of the colder and heavier air with a further fall in temperature in the hollows and pockets, where the lower stations are located, while the warmer and lighter air above, as it is drawn into an approaching cyclone, flows over the summits and the upper slopes.
The Cyclonic or Overflow Type is characterized by moderate to strong winds and rapidly falling pressure, with a well-developed cyclone approaching. During inversions of this type the low temperatures at the base stations are due to the confinement of air, already cold, in the pockets and narrow valleys, while the strong southerly winds, which usually prevail in the North Carolina region, bring warm air to the higher stations,
and although these winds soon draw the colder air out of the pockets, sometimes this does not occur in time to prevent a strong inversion. The Cyclonic Type occurs most frequently in the winter months, when there is pronounced storm activity.
Each one of the three types often merges into one of the two others, so that many of the weaker inversions may be placed in any two of the three types. There is often no sharp