Ozone Heating and Radiative Equilibrium in the Lower Stratosphere

Abstract

Extensive measurements of the vertical ozone distribution from the North American ozonesonde network have provided a basis for detailed investigation of radiative processes in the lower stratosphere. Calculations were made of the average monthly heating rates over all latitudes due to the absorption of both direct and reflected solar short-wave radiation in the pressure interval of 50 to 10 mb. The ozone heating rates were combined with estimates of solar infrared heating derived from the calculations of Houghton to yield estimates of the total solar heating distribution at selected levels in the lower stratosphere. It was found that the solar heating rates are primarily dependent on the solar zenith angle and the duration of sunlight. These variables accounted for over 94% of the variance in the calculated mean monthly beating rates at the 10-, 15-, and 25-mb pressure levels. Comparative analysis of the total solar heating rates and the observed temperature structure led to the surprising result that the distribution of mean monthly temperature in the lower stratosphere from May through October can be reconstructed from the distribution of total solar heating with a standard error of less than 2K. This result indicates both a close approach to radiative equilibrium in the 50- to 10-mb pressure interval in the warmer half year and a remarkably strong linear dependence of average infrared cooling on the mean temperature. The exponential response time for the infrared cooling component its estimated to be 8.5 days at 10 mb and 17 5 days at 50 mb.