RADIATIVE HEATING IN THE TROPOSPHERE AND LOWER STRATOSPHERE

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  • 1 Institute of Atmospheric Physics, The University of Arizona, Tucson, Ariz.
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Abstract

Brooks' method for computing rates of atmospheric heating which is due to radiation by water vapor has been adapted to the digital computer, allowing investigation of the following aspects of the method: the effect of spacing of data points on heating rate profiles, the dependence of heating rates upon the flux emissivity data, and the influence of the form of the pressure correction factor upon heating rates. Two cases of practical interest have been considered. The first is the effect of radiative heating upon tropospheric temperature inversions. It is concluded, in agreement with the results of Staley, that radiative heating acts to strengthen the inversion when water vapor mixing ratios within the inversion layer are small. The second case studied the consequences of the presence of substantial quantities of water vapor in the stratosphere. Cooling rates ranging up to 2.5° C. day−1 were obtained over a winter cross section of the Northern Hemisphere having a constant relative humidity of 5 perccnt in the stratosphere. Decreases in the net radiative flux, as evidenced by small heating rates in the region of the tropopause at low latitudes, agree with observations by Riehl in the Caribbean and by Kuhn and Suomi in the United States. The fact that this effect was not present when mixing ratios were allowed to decrease rapidly above the tropopause lends support to the argument that substantial quantities of water vapor are present in the stratosphere.

Abstract

Brooks' method for computing rates of atmospheric heating which is due to radiation by water vapor has been adapted to the digital computer, allowing investigation of the following aspects of the method: the effect of spacing of data points on heating rate profiles, the dependence of heating rates upon the flux emissivity data, and the influence of the form of the pressure correction factor upon heating rates. Two cases of practical interest have been considered. The first is the effect of radiative heating upon tropospheric temperature inversions. It is concluded, in agreement with the results of Staley, that radiative heating acts to strengthen the inversion when water vapor mixing ratios within the inversion layer are small. The second case studied the consequences of the presence of substantial quantities of water vapor in the stratosphere. Cooling rates ranging up to 2.5° C. day−1 were obtained over a winter cross section of the Northern Hemisphere having a constant relative humidity of 5 perccnt in the stratosphere. Decreases in the net radiative flux, as evidenced by small heating rates in the region of the tropopause at low latitudes, agree with observations by Riehl in the Caribbean and by Kuhn and Suomi in the United States. The fact that this effect was not present when mixing ratios were allowed to decrease rapidly above the tropopause lends support to the argument that substantial quantities of water vapor are present in the stratosphere.

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