Rapid computation of the radiative absorption rate in the v 3 mode of mesospheric and lower thermospheric ozone

Abstract

We have developed an algorithm to calculate rapidly and accurately the rate (photons-molecule -1-sec -1) at which the ozone v 3 fundamental band absorbs i.r. radiation in the terrestrial upper mesosphere and lower thermosphere. Accurate knowledge of this rate is essential for studies of non-LTE processes in ozone and for estimating ozone concentrations from measurements of non-LTE i.r. emission from the middle atmosphere. In our algorithm, the 1252 ozone v 3 fundamental lines that govern radiative absorption are divided into 13 groups according to line strength. The absorption rate due to a single line representative of the mean line strength of each group is then calculated. The total absorption rate is obtained by multiplying the absorption rate for each mean line by the total number of lines within each group and adding the resultant products for all 13 groups. We also incorporate several other approximations, such as assuming that each mean line has the same Voigt line shape, which significantly reduces the number of Voigt function evaluations. The algorithm preserves the accuracy of detailed, time-consuming line-by-line approaches while requiring only a fraction of the CPU time of such techniques.