PHOTODISSOCIATION OF O-2 AND H2O IN THE MIDDLE ATMOSPHERE - COMPARISON OF NUMERICAL-METHODS AND IMPACT ON MODEL O-3 AND OH

We have compared three photochemical diurnal models of O3 and OH in th e upper stratosphere and mesosphere which use different techniques for calculating the absorption of solar ultraviolet radiation by the O2 S chumann-Runge bands. One model uses a detailed line-by-line representa tion of the O2 cross section from 1750-2050 angstrom, while the two ot hers use lower resolution, parameterized cross sections. Using the par ameterized cross sections, the calculated O3 profiles for both day and night agree with those obtained from the line-by-line model to within 6%. This appears to eliminate inaccuracies in the parameterized O2 cr oss section as a major cause of previously reported model O3 deficits. A portion of the residual differences from the line-byline model are attributed to inaccuracies in the calculated H2O photolysis rate. A pa rameterized H2O cross section is offered which improves the accuracy o f this calculation.