TEMPERATURE, TERRESTRIAL. The distri bution of heat in the atmosphere depends to some extent on its direct absorption of solar radiations, and especially the absorption at the upper surface of the clouds, but is principally governed by the angular altitude of the sun and the contact of the air with the ground and the ocean. The numerous irregularities give rise to the great currents of air as well as to the local winds, and the latter carry the heat and the temperature rapidly from one part of the globe to the other, so that ultimately the atmospheric temperature is almost equally controlled by the winds on the one hand and the oceans, continents, rain, snow, and cloud on the other. The typical continental climates experi ence great diurnal and annual ranges of tem perature, and the typical oceanic climates show a small range.
The distribution of temperature on any level surface at any depth below or height above sea level is shown by means of isotherms, which are drawn through all places that have the same temperature at any moment, or the same month ly or annual mean temperature. Charts show
ing these isotherms have been published by vari ous meteorological services for the air and the land, and by various hydrographic offices for the oceans. The highest mean annual temperatures occur within the tropics and especially over the land areas of Northern Africa and Southern Asia, with corresponding small regions in Cen tral America and the northern portion of South America. The lowest mean annual temperatures are found in Northern Siberia and the northern portions of British America, which represent the southern extension of a large Arctic area of low temperature. See CLIMATE.