The pattern of radiative heating and cooling in the troposphere and lower stratosphere

Abstract

For any meteorological effects of radiation, only those constituents of the air which have a very strong absorption in the infra-red are involved; these are water vapour and carbon dioxide. Several methods have been developed (Mügge & Möller 1932 a, b ; Elsasser 1942; Yamamoto 1952) for computing the radiation flux, and numerous calculations of these fluxes and of the cooling rates have been performed in the last 25 years (Ludwig 1935; Kortiim 1939; Thompson & Neiburger 1955). The results are summarized in figure 1, which shows the distribution of the tem­perature and of the cooling rate by water vapour in some characteristic atmospheres. The lower levels of the tropical atmosphere have a small cooling rate because the higher layers are very humid and the lower layers are thus sheltered from radiation losses. A contrary effect occurs at 30° latitude, where a very dry subsiding middle atmosphere is observed above a very wet trade-wind layer. In the arctic atmosphere a high cooling rate results for 1.5 km as a consequence of the conduction-like effect of radiation. The maximum values of the cooling rate are attained in the higher troposphere; they shift to somewhat lower levels with decreasing temperature and decreasing water-vapour content, from 10.5 km in the tropics to 7 km in middle latitudes and 4 km in the arctic. Apart from the extreme conditions in the arctic, the curves do not show much difference, and it is probable that all the differences may be understood by considering only the different amount of precipitable water.