Appendix No. II

THE ANTARCTIC CLIMATE

BY

HENRYK ARCTOWSKI

The following is a preliminary account of some of the additions to our knowledge of the meteorology of higher southern latitudes contributed by the recent Belgian Antarctic Expedition.

These desolate antarctic regions, still so little explored, present many physical problems of the highest interest; the question of their climate, attacked as early as the time of Croll, must prove a subject of exhaustive investigation in the immediate future. The results I have obtained were not originally intended for publication in their present form, because the mean values involved can only be regarded as first approximations; however, it appears that my provisional numbers are sufficiently exact to indicate the general nature of the climatic régime in parts of the globe about which we have been, up to the present, practically without information. The fact that other antarctic expeditions are about to set out has decided me to publish my figures as they stand.

For the purposes of our inquiry, it is a matter of indifference whether an antarctic continent exists or not; we have undoubtedly to deal with a continuous surface of ice, which the meteorologist must regard as a land surface as opposed to an open sea. This ice-cap is entirely isolated by an ocean which surrounds it, and is subjected to the peculiar conditions of polar day and night. Hence the first points to be considered are the average distribution of pressure and the direction of the prevailing winds. The positions (about 81° and 95° west longitude, and 69° 50′ and 71° 30′ south latitude) show a relatively small distance from the open sea and great distance from the pole. In consequence we experienced two distinct types of climate according to the direction of the wind,—a continental and an oceanic,—in effect a coastal climate depending on the passage of cyclones which varied in frequency with the seasons. This seems to be the key of the whole position. As regards details, I take into consideration the mean and minimum temperatures and the barometric pressures, the direction of wind, the amount of cloud, and the amount of precipitation.

Table I. gives the mean values obtained from hourly observations of temperature made on board the Belgica during her drift in the ice.

July was the coldest month; its mean temperature was -23.5° C. (-10.3° F.), and the lowest temperature observed during the month, -37.1° C. (-34.8° F.). The extreme minimum of temperature was observed in September, -43.1° C. (-45.6° F.).

The warmest month was February, with a mean temperature of -1.0° C. (30.2° F.), and minimum for the month, -9.6° C. (14.7° F.).

If we regard June, July, and August as the antarctic winter months, and December, January, and February as summer, we may take it that the mean winter temperature is -16.8° C. (1.8° F.), and the mean for summer, -1.5° C. (29.3° F.).

Table II. shows the minimum temperature for each month. The maximum temperatures are less interesting; the winter average is -1° to 0° C. (30° to 32° F.); the absolute maximum for the equinoctial months is 0° to 1° C. (32° to 34° F.), and for summer, 2° C. (36° F.).

These tables show that between the seventieth and seventy-first parallels of the southern hemisphere, and amid the ice of the Antarctic Ocean, first, the mean temperature is lower than that of the northern coast of Spitsbergen—Mossel Bay, 1872–73, -8.9° C. (16° F.); second, the minimum temperature is quite as low as the minima observed on the east side of Greenland (Sabine Island and Scoresby Sound); and third, that the mean temperature of the three summer months is lower than the corresponding mean in the ice of the Arctic Ocean—the observations of the Fram give a mean for June, July, and August of -1.2° C. (29.8° F.). Note that the calculations of Spitaler and Supan give a mean temperature for the parallel of 70° north latitude of -10.2° C. (13.6° F.). If we consider that a considerable fraction of the seventieth parallel of south latitude is land, we can suppose that it may have a mean temperature as low as the seventieth degree north, and include a pole of cold with lower temperature, as the Asiatic or North American poles of cold.

As in the case of the mean temperatures, the values I am able to give for mean barometric pressure must be regarded only as first approximations. During our drift in the pack-ice hourly observations were made with a marine barometer and with an aneroid. I have not yet been able to apply exact corrections to these observations, but if we bear in mind that while the temperature correction is negative, the correction for latitude is positive, and that for temperatures about 13° to 15° C. (55° to 60° F.) these corrections are numerically nearly equal, we can accept the uncorrected values as near enough for our present purpose. Table III. gives the averages of the aneroid observations, calculated to whole millimetres only. The mean for the year is 744.7 mm. (29.319 inches).

FIG. 1.

Tables IV. and V. give the principal minima and maxima of pressure observed; the values are reduced to the freezing-point and gravity at 45° latitude. The lowest pressure observed during our wintering was 711.74 mm. (28.022 inches), and the highest 772.14 mm. (30.400 inches), a range of 60.40 mm. (2.378 inches). Table VI. gives the monthly variations of the barometer, the mean value of which amounts to 34.30 mm. (1.350 inches), showing even more clearly than Table IV. that the cyclonic belt extends beyond the polar circle. From this table it appears, further, that the three months of almost continuous daylight (November, December, and January) are characterised by a very small variation of pressure—only 23.95 mm. (0.943 inch). The three corresponding months of winter have also a mean less than those for the intermediate or equinoctial months. Compare this with the mean pressures (Table III.). The differences between the annual and monthly means (Table VII.) show that February, March, and April form a negative group, in which the pressure is relatively low; the three months of polar night form another group of maximum barometric pressure; then follow August, September, and October, months of decreasing pressure, a group which, although not actually negative, forms a distinct secondary minimum; and lastly, three months of polar day forming a secondary maximum of pressure. The general result is illustrated in Fig. 1,—high pressure at the solstices, low pressure at the equinoxes,—and the existence of a direct simple relation between the barometric pressure and the progress of the sun is at once obvious.

Table VIII. gives the observed wind directions: the figures indicate the number of hours during which the wind blew from each direction during the twelve months, the sums constituting the “wind-rose” of the point of observation. Fig. 2 shows that winds blow from northerly and southerly points with almost equal frequency, and that easterly winds predominate over westerly. The directions of greatest frequency were west, east, and north-east.

FIG. 2.

The monthly wind-roses show some interesting seasonal variations in the prevailing directions of the wind; we note specially the predominance of north-east to south-east over westerly winds from November to February, and the relative frequency of westerly winds during June, July, and August (Fig. 3). The figures show that, on the whole, the station was beyond the westerly wind region, although at certain seasons the westerly system did extend as far south.

FIG. 3.

Some further points must be referred to in describing the climatic conditions we experienced. The temperature of the air is doubtless the most important element in the study of climate; but it seems to me that its importance is relatively less in polar regions than in other parts of the globe. In polar latitudes the human organism is chiefly influenced by the absence of the sun during the night of winter. In the summer, on the other hand, the radiant heat of the sun is so strongly concentrated that the temperature of the air scarcely measures the warmth we feel. Further, the action of the solar rays is directly beneficial—the sun strengthens and reanimates. And besides direct insolation, the diffused daylight itself must be considered. One feels quite different under a cloudless vault and under a sky overcast and sombre. The presence or absence of the sun is a much more important matter to us than the state of the thermometer.

The wind is another extremely important factor from the physiological point of view. In calm weather a temperature of -20° C. (-4° F.) is quite tolerable, even agreeable if the sun is shining; but with a light breeze one feels the cold at once, and in strong wind it is impossible to remain long in the open air with so low a temperature. It appears to me that humidity plays a quite secondary part in the physiology of the polar climate—at least, at low temperatures; in any case, the humidity of the atmosphere rarely makes itself felt.

Some actinometric observations will serve to indicate the intensity of radiant heat. At 2 P. M. on December 30, the temperature of the air being -0.2° C. (31.6° F.), the black-bulb thermometer read 45.1° C. (113.2° F.) in the sun, which explains why in reality the weather felt very warm.

The sky was usually overcast, most frequently with a thick layer of stratus, which formed a uniform gray covering, and often persisted for days or even weeks together, with only short breaks. Table IX. shows the state of the sky during each month of the year.

The number of days during which the air was not saturated, i.e., on which the hygrometer indicated humidity less than ninety per cent., was, in October, 12; November, 18; December, 22; January, 15; and February, 11.

If we include ice-deposits from fog and similar precipitation, we find that snowfall is recorded on 257 days of the year, made up as shown on the first column of Table X. The second column of Table X. shows the number of days on which rain (even a few drops) was recorded. Speaking generally, it may be said that the weather was extremely cloudy, that fogs were frequent, that snow fell on many days, and that the air was saturated nearly the whole time.

Table XI. gives particulars with regard to wind force.

Table I.—Mean Temperature.

°C °F
1898. March -9.1 -9.1 15.6 15.6
April -11.8 10.8
May -6.5 20.3
June 15.5 -16.8 4.1 1.8
July 23.5 -10.3
August -11.3 11.7
September -18.5 -11.1 -1.3 12.0
October -7.9 17.8
November -6.9 19.6
December -2.2 -1.5 28.0 29.3
1899. January -1.2 29.8
February -1.0 30.2
Year -9.6 14.7

Table II.—Monthly Minima of Temperature.

°C °F
1898. February 23, at 10 p.m. -7.6 18.3
March 15, at 4 a.m. -20.3 -4.5
April 3, at 6 p.m. -26.5 -15.7
May 29, at 8 p.m. -25.2 -13.4
June 3, at 6 p.m. -30.0 -22.0
July 17, at 10 p.m. -37.1 -34.8
August 28, at 3 a.m. -29.6 -21.3
September 8, at 4 a.m. -43.1 -45.6
October 25, at 3 a.m. -26.3 -15.3
November 2, at 4 a.m. -21.4 -6.5
December 2, midnight -14.5 5.9
1899. January 2, at 2 a.m. -8.1 17.4
February 11, at 2 a.m. -9.6 14.7
March 4, midnight -12.0 10.4

Table III.—Monthly Means (Approximate) of Barometric Pressure.

- MM. INCHES.
1898. February[1] 738.5 29.075
March 741.4 29.190
April 735.6 28.961
May 746.3 29.382
June 749.5 29.508
July 747.8 29.441
August 747.2 29.418
September 745.5 29.351
October 744.7 29.319
November 746.0 29.371
December 748.2 29.457
1899. January 747.3 29.422
February 736.5 28.997
Year 744.7 29.319

[1] Latter half of month only.

Table IV.—Minimum Pressures Observed.

- REDUCED TO
FREEZING-POINT.		 REDUCED TO FREEZING-POINT
AND LAT. 45°.
MM. INCHES. MM. INCHES.
1898. February 18, at 6 a.m. 724.53 28.526 725.93 28.581
March 22, at 4 a.m. 719.96 28.345 721.48 28.405
April 20, at 3 a.m. 714.66 28.136 716.15 28.195
May 10, at 11 p.m. 730.26 28.751 731.78 28.811
June 21, at 1 a.m. 733.58 28.881 735.11 28.941
July 31, at 2 a.m. 731.77 28.811 733.28 28.870
August 12, at 4 a.m. 715.81 28.182 717.31 28.241
September 22, at 6 a.m. 719.29 28.319 720.77 28.377
October 23, at 4 a.m. 722.06 28.428 723.53 28.486
November 19, at 3 p.m. 731.33 28.793 732.82 28.852
December 22, at 10 p.m. 735.52 28.958 737.01 29.016
1899. January 30, at 10 p.m. 733.92 28.895 735.43 28.955
February 17, at 11 p.m. 718.59 28.292 720.08 28.350
March 2, at 3 a.m. 710.26 27.963 711.74 28.022

Absolute minimum, 711.74 mm. = 28.022 inches.

Table V.—Maximum Pressures Observed.

- REDUCED TO
FREEZING-POINT.		 REDUCED TO FREEZING-POINT
AND LAT. 45°.
MM. INCHES. MM. INCHES.
1898. February 11, at 4 p.m. 755.82 29.757 757.11 29.808
March 29, at 1 a.m. 755.35 29.739 756.95 29.802
April 26, at 7 a.m. 753.80 29.678 755.37 29.739
May 13, at 4 p.m. 764.28 30.090 765.90 30.154
June 11, at 1 a.m. 770.48 30.334 772.14 30.400
July 18, at 8 p.m. 761.53 29.983 763.10 30.044
August 29, at 6 p.m. 765.43 30.135 766.99 30.197
September 16, at 9 p.m. 757.77 29.834 759.31 29.894
October 12, at 8 a.m. 764.80 30.111 766.35 30.172
November 13, at 4 a.m. 754.05 29.688 755.58 29.748
December 18, at 5 a.m. 757.65 29.829 759.20 29.890
1899. January 24, at 8 p.m. 760.76 29.951 762.33 30.013
February 22, at 3 a.m. 751.63 29.593 753.17 29.653

Absolute maximum, 772.14 mm. = 30.400 inches.

Table VI.—Maximum Variations of Pressure, and Means of those Variations.

MM. INCHES.
1899. February 33.09 35.93 1.303
1898. March 35.47 1.397
April 39.22 1.544
May 34.12 33.66 1.343
June 37.03 1.458
July 29.82 1.174
August 49.68 43.68 1.955
September 38.54 1.518
October 42.82 1.686
November 22.76 23.95 0.897
December 22.19 0.874
1899. January 26.90 1.059
Mean 34.30 1.350

Extreme range for the year: 772.14—711.74 = 60.40 mm.

30.400—28.022 = 2.378 inches.

Table VII.—Differences of Monthly Means of Pressure from the Mean of the Year.

The + sign indicates pressure greater than the mean, the - sign pressure less than the mean.

MM. INCHES.
1899. February -8.2 -0.323 minimum.
1898. March -3.3 -0.130
April -9.1 -0.358
May +1.6 +0.063 maximum.
June +4.8 +0.189
July +3.1 +0.122
August +2.5 +0.098 2nd minimum.
September +0.8 +0.031
October 0.0 0.000
November +1.3 +0.051 2nd maximum.
December +3.5 +0.138
1899. January +2.6 +0.102

Table VIII.—Table of Wind Directions.

The figures show the number of hours during which the wind blew from each direction.

N.N.N.E.E.E.S.S.S.S.S.W.W.W.N.N.
N.E.N.S.E.S.S.W.S.N.W.N.
E.E.E.E.W.W.W.W.
1898.
March14263860685034308222645678222210
April30221327846476593221252051495031
May1001217281733479121765756183
June1422263334252892487638191873716
July22101--24723170542848388148254
August32143829269345191047561417610438
Sept.51247444462228144916472159452417
Oct.473146845117184124697491428332
Nov.34356993793221142131372838281821
Dec.312539267107551621246358445117
1899.
Jan.816124156104845272201228168------
Feb.32427049111997237221013233513176
387375624599705608442351394207519445882490452265

Table IX.

Column 1 shows number of days of continuous fog or overcast sky.

Column 2 shows number of days with sky partially clear for several hours in succession (cloud amount 30 per cent. or more).

Column 3 shows number of days on which fog was observed.

123
March61514
April101426
May15827
June51628
July72217
August91525
September91414
October161223
November131018
December91313
January17617
February21123

Table X.

Column 1 shows the number of days on which snow was recorded.

Column 2 shows the number of days on which rain was recorded.

12
March13—
April22—
May304
June24—
July14—
August261
September19—
October252
November25—
December18—
January194
February223
Year25714

Table XI.

Column 1 shows the number of days of calm, or of wind not exceeding force 1.

Column 2 shows the number of days of wind force less than 4.

12
March011
April25
May313
June311
July1525
August315
September720
October411
November821
December421
January524
February112