Model ozone photochemistry on the basis of Solar Mesosphere Explorer mesospheric observations

Abstract

Morning and afternoon mesospheric ozone profiles (50–90 km) measured by the Solar Mesosphere Explorer (SME) satellite are analyzed with one‐dimensional photochemical models. The observed ozone abundances are 40% and 100% greater than the model ozone abundances at 50 and 80 km, respectively, assuming standard chemistry and rate coefficients. A Monte Carlo analysis for model ozone abundances that includes uncertainties in kinetic rate coefficients indicates that the model‐data disagreement exceeds 2 standard deviations. The majority of the disagreement must be due to errors in the rate of odd‐hydrogen catalytic destruction of ozone, unless the rate coefficient for O + O 2 + M → O 3 + M is significantly (>50%) in error. Diurnal model calculations are compared with SME observations of ozone profiles at ∼0400 and 1400 LT for high northern summer latitudes. Analysis of the ratios of these early morning and midafternoon ozone profiles provides the additional constraint that larger odd‐oxygen production rates are required if lower odd‐hydrogen activity is invoked to increase model O 3 abundances. The increase in odd‐oxygen production must be solar zenith angle independent in the mesosphere, ruling out significant changes in the Schumann‐Runge band O 2 opacities from Allen and Frederick (1982). However, an increase in three‐body formation of O 3 is also consistent with the observed morning/afternoon ratios. Any of the above changes are consistent with an improvement in model ozone comparisons with stratospheric observations. Finally, we find evidence for diurnal variations in mesospheric ozone above 80‐km altitude, which are likely related to diurnal variations in vertical transport.