Three-dimensional modeling of ozone on Mars -: art. no. E07004

[ 1] We present the first three-dimensional model simulations of ozone on Mars. The model couples a state-of-the-art gas-phase photochemical package to the general circulation model developed at Laboratoire de Meteorologie Dynamique (LMD). The results do not contradict the classical picture of a global anticorrelation between the ozone (O-3) and water vapor columns. However, the quantitative approach shows significant departures from this relationship, related to substantial orbital variations in the O-3 vertical distribution. Over the period L-s = 180degrees - 330degrees, low-latitude to midlatitude O-3 is essentially confined below 20 km, has a weak diurnal cycle, and is largely modulated by topography. During the rest of the year (L-s = 330degrees - 180degrees) the model predicts the formation of an O-3 layer at 25 - 70 km altitude, characterized by nighttime densities about one order of magnitude larger than during the day. Throughout the year, high-latitude O-3 peaks near the surface and reaches maximum integrated amounts ( similar to 40 mm-atm) in the winter polar vortex, with considerable (30 to 50%) dynamically induced day-to-day variations. The most stringent comparison to date with O-3 observational data reveals contrasted results. A good quantitative agreement is found in the postperihelion period (L-s = 290degrees - 10degrees), but the model fails to reproduce O-3 columns as large as those measured near aphelion (L-s = 61degrees - 67degrees). Current uncertainties in absorption cross sections and gas-phase kinetics data do not seem to provide credible explanations to explain this discrepancy, which may suggest the existence of heterogeneous processes.