Three-dimensional modeling of ozone on Mars
Résumé
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 Me´te´orologie Dynamique (LMD). The
results do not contradict the classical picture of a global anticorrelation between the ozone
(O3) and water vapor columns. However, the quantitative approach shows significant
departures from this relationship, related to substantial orbital variations in the O3
vertical distribution. Over the period Ls = 180–330, low-latitude to midlatitude O3 is
essentially confined below 20 km, has a weak diurnal cycle, and is largely modulated
by topography. During the rest of the year (Ls = 330–180) the model predicts the
formation of an O3 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
O3 peaks near the surface and reaches maximum integrated amounts (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 O3 observational data reveals
contrasted 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 measured
near aphelion (Ls = 61–67). 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.
Domaines
Planétologie
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