Seasonal and other temperature changes in the Antarctic atmosphere

Abstract

AbstractThe annual variation of temperature in Antarctica has interesting properties: it is largest in the stratosphere (50° to 60°C), smaller at the surface (20° to 40°C) and smallest in the troposphere (10°C). During the winter night the troposphere temperature decreases only slightly while the stratosphere temperature drops steadily at about 1/4°C per day. This differential cooling, which weakens and at times wipes out the tropopause, is caused, on the one hand, by intense horizontal advection of maritime air into the Antarctic troposphere, and, on the other hand, by very little advection through the strong stratospheric jet stream encircling Antarctica.This ventilation of the Antarctic troposphere by warm marine air causes large portions of Antarctica to exhibit the kernlose winter‐temperature curve instead of the sharp winter minimum usually found in polar continental climate. Anomalously high June temperatures in the lower troposphere at Little America are attributed to intense cyclones which form in the Ross Sea area and advect air from the lightly ice‐clad or open ocean located not too far north of the Ross Sea.Large deviations in average monthly temperatures are found in the Ross Sea area which are undoubtedly a reflection of large year‐to‐year circulation changes in that area.The Antarctic and Arctic stratospheres exhibit quite different temperature behaviours after the winter solstice. The Antarctic stratosphere continues to cool until the sun returns and then warms as much as 50°C in 1 month. On the other hand, the Arctic stratosphere exhibits a warming of 30° to 40°C, sometimes beginning 6 weeks before the sun returns.A secular trend of temperature since 1912 of + 2·6°C at Little America (78° 12'S, 162° 15′W) compares with a + 6·2°C trend at Spitsbergen (78° 04′N, 13° 38′E).Finally, temperature and outgoing radiation observations made at the South Pole I.G.Y. Station during the cold period of 19‐24 April 1958 are presented to illustrate quantitatively the important effect of warm cloud radiation on surface air temperature and its vertical gradient.