Page:EB1911 - Volume 06.djvu/540

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the influence of the cold offshore monsoon, and the summers are warm and rainy. Rainfalls of 40 in. are found on the east coasts of Korea, Kamchatka and Japan, while in North America, which is more open, they reach farther inland. Japan, although occupying an insular position, has a modified continental rather than a marine climate. The winter monsoon, after crossing the water, gives abundant rain on the western coast, while the winter is relatively dry on the lee of the mountains, on the east. Japan has smaller temperature ranges than the mainland.

Mountain Climates.—The mountain climates of the temperate zone have the usual characteristics which are associated with altitude everywhere. If the altitude is sufficiently great the decreased temperature gives mountains a polar climate, with the difference that the summers are relatively cool while the winters are mild owing to inversions of temperature in anticyclonic weather. Hence the annual ranges are smaller than over lowlands. At such times of inversion the mountain-tops often appear as local areas of higher temperature in a general region of colder air over the valleys and lowlands. The increased intensity of insolation aloft is an important factor in giving certain mountain resorts their deserved popularity in winter (e.g. Davos and Meran). Of Meran it has been well said that from December to March the nights are winter, but the days are mild spring. The diurnal ascending air currents of summer usually give mountains their maximum cloudiness and highest relative humidity in the warmer months, while winter is the drier and clearer season. This is shown in curve M, fig. 13. The clouds of winter are low, those of summer are higher. Hence the annual march of cloudiness on mountains is usually the opposite of that on lowlands.

Characteristics of the Polar Zones.

General.—The temperate zones merge into the polar zones at the Arctic and Antarctic circles, or, if temperature be used as the basis of classification, at the isotherms of 50° for the warmest month, as suggested by Supan. The longer or shorter absence of the sun gives the climate a peculiar character, not found elsewhere.

Beyond the isotherm of 50° for the warmest month forest trees and cereals do not grow. In the northern hemisphere this line is well north of the Arctic circle in the continental climate of Asia, and north of it also in north-western North America and in northern Scandinavia, but falls well south in eastern British America, Labrador and Greenland, and also in the North Pacific Ocean. In the southern hemisphere this isotherm crosses the southern extremity of South America, and runs fairly east and west around the globe there. The conditions of life are necessarily very specialized for the peculiar climatic features which are met with in these zones. There is a minimum of life, but more in the north polar than the south polar zone. Plants are few and lowly. Land animals which depend upon plant food must therefore likewise be few in number. Farming and cattle-raising cease. Population is small and scattered. There are no permanent settlements at all within the Antarctic circle. Life is a constant struggle for existence. Man seeks his food by the chase on land, but chiefly in the sea. He lives along, or near, the sea-coast. The interior lands, away from the sea, are deserted. Gales and snow and cold cause many deaths on land, and, especially during fishing expeditions, at sea. Under such hard conditions of securing food, famine is a likely occurrence.

In the arctic climate vegetation must make rapid growth in the short, cool summer. In the highest latitudes the summer temperatures are not high enough to melt snow on a level. Exposure is therefore of the greatest importance. Arctic plants grow and blossom with great rapidity and luxuriance where the exposure is favourable, and where the water from the melting snow can run off. The soil then dries quickly, and can be effectively warmed. Protection against cold winds is another important factor in the growth of vegetation. Over great stretches of the northern plains the surface only is thawed out in the warmer months, and swamps, mosses and lichens are found above eternally frozen ground. Direct insolation is very effective in high latitudes. Where the exposure is favourable, snow melts in the sun when the temperature of the air in the shade is far below freezing.

Arctic and antarctic zones differ a good deal in the distribution and arrangement of land and water around and in them. The southern zone is surrounded by a wide belt of open sea; the northern, by land areas. The northern is therefore much affected by the conditions of adjacent continental masses. Nevertheless, the general characteristics are apparently much the same over both, so far as is now known, the antarctic differing from the arctic chiefly in having colder summers and in the regularity of its pressure and winds. Both zones have the lowest mean annual temperatures in their respective hemispheres, and hence may properly be called the cold zones.

Temperature.—At the solstices the two poles receive the largest amounts of insolation which any part of the earth’s surface ever receives. It would seem, therefore, that the temperatures at the poles should then be the highest in the world, but as a matter of fact they are nearly or quite the lowest. Temperatures do not follow insolation in this case because much of the latter never reaches the earth’s surface; because most of the energy which does reach the surface is expended in melting the snow and ice of the polar areas; and because the water areas are large, and the duration of insolation is short.

A set of monthly isothermal charts of the north polar area, based on all available observations, has been prepared by H. Mohn and published in the volume on Meteorology of the Nansen expedition. In the winter months there are three cold poles, in Siberia, in Greenland and at the pole itself. In January the mean temperatures at these three cold poles are –49°, –40° and –40° respectively. The Siberian cold pole becomes a maximum of temperature during the summer, but the Greenland and polar minima remain throughout the year. In July the temperature distribution shows considerable uniformity; the gradients are relatively weak. A large area in the interior of Greenland, and one of about equal extent around the pole, are within the isotherm of 32°. For the year a large area around the pole is enclosed by the isotherm of –4°, with an isotherm of the same value in the interior of Greenland, but a local area of –7.6° is noted in Greenland, and one of –11.2° is centred at lat. 80° N. and long. 170° E.

The north polar chart of annual range of temperature shows a maximum range of about 120° in Siberia; of 80° in North America; of 75.6° at the North Pole, and of 72° in Greenland. The North Pole obviously has a continental climate. The minimum ranges are on the Atlantic and Pacific Oceans. The mean annual isanomalies show that the interior of Greenland has a negative anomaly in all months. The Norwegian sea area is 45° too warm in January and February. Siberia has +10.8° in summer, and –45° in January. Between Bering Strait and the pole there is a negative anomaly in all months. The influence of the Gulf Stream drift is clearly seen on the chart, as it is also on that of mean annual ranges.

For the North Pole Mohn gives the following results, obtained by graphic methods:—

Mean Temperatures at the North Pole.

Jan. Feb. Mar. Apr.  May.  June. July. Aug. Sept. Oct. Nov. Dec.  Year. 
–41.8° –41.8° –31.0° –18.4°  8.6°  28.4°  30.2°  26.6°  8.6° –11.2° –27.4° –36.4° –8.9°

It appears that the region about the North Pole is the coldest place in the northern hemisphere for the mean of the year, and that the interior ice desert of Greenland, together with the inner polar area, are together the coldest parts of the northern hemisphere in July. In January, however, Verkhoyansk, in north-eastern Siberia, just within the Arctic circle, has a mean temperature of about –60°, while the inner polar area and the northern interior of Greenland have only –40°. Thus far no minima as low as those of north-eastern Siberia have been recorded in the Arctic.

For the Antarctic our knowledge is still very fragmentary,