Evidence for the existence of the "emission layer" in the atmosphere

Abstract

The theory of radiative equilibrium demands that on the average the total amount of energy absorbed by the earth and its atmosphere in the form of short-wave solar radiation should be exactly equal to the total amount of energy given back to space in the form of long-wave heat radiation. From a study of the absorbing and radiating properties of the atmosphere, F. Albrecht arrived at the fundamental result that the major contribution to the long-wave heat radiation into outer space originates from a layer of some three to four kilometres thickness in the upper troposphere, which he designates as the "Emission Layer". The emission layer is thus a portion of the upper atmosphere which is continually cooling due to radiative loss of heat. The height of the emission layer is a function of the water vapour content of the atmosphere; it is more when the atmosphere is hot and humid and less when the atmosphere is cold and dry. The author has made a detailed study of the thermal structure of the atmosphere over Agra based on the results of sounding balloon ascents over a period of ten years. A number of interesting features find a ready explanation on the assumption that the emission layer over Agra is located approximately between 11 and 14 gkm. in the monsoon months and between 8 and 11 gkm. during the remaining months, -an assumption in conformity with Albrecht's work. The observed seasonal variations in the thermal structure of the atmosphere over Agra thus lend, strong evidence for the existence of the emission layer in the atmosphere and the variation of its altitude depending upon the moisture content of the atmosphere.