Three-dimensional modeling of ozone on Mars

International audienceWe present the first three-dimensional model simulations of ozone on Mars. Themodel couples a state-of-the-art gas-phase photochemical package to the generalcirculation model developed at Laboratoire de Me´te´orologie Dynamique (LMD). Theresults do not contradict the classical picture of a global anticorrelation between the ozone(O3) and water vapor columns. However, the quantitative approach shows significantdepartures from this relationship, related to substantial orbital variations in the O3vertical distribution. Over the period Ls = 180–330, low-latitude to midlatitude O3 isessentially confined below 20 km, has a weak diurnal cycle, and is largely modulatedby topography. During the rest of the year (Ls = 330–180) the model predicts theformation of an O3 layer at 25–70 km altitude, characterized by nighttime densities aboutone order of magnitude larger than during the day. Throughout the year, high-latitudeO3 peaks near the surface and reaches maximum integrated amounts (40 mm-atm) inthe winter polar vortex, with considerable (30 to 50%) dynamically induced day-to-dayvariations. The most stringent comparison to date with O3 observational data revealscontrasted results. A good quantitative agreement is found in the postperihelion period(Ls = 290–10), but the model fails to reproduce O3 columns as large as those measurednear aphelion (Ls = 61–67). Current uncertainties in absorption cross sections andgas-phase kinetics data do not seem to provide credible explanations to explain thisdiscrepancy, which may suggest the existence of heterogeneous processes