On Forcing the Winter Polar Warmings in the Martian Middle Atmosphere during Dust Storms

Abstract

Using a Martian general circulation model, we investigated the changes in the meridional circulation during planet-encircling dust storms on Mars that produce strong temperature vertical inversions in the middle atmosphere over winter polar regions. It is shown that vigorous poleward and downward transport, and, consequently, the adiabatic heating are caused by dissipating thermal tides, planetary and resolved small-scale gravity waves and eddies in almost equal degree. The increase of tidal forcing is mainly due to a stronger excitation in the summer hemisphere. Contribution of the stationary planetary wave (SPW) with the zonal wavenumber s ¼ 1i ncreases during dust storms due to intensified generation in the lower atmosphere as well as due to more favorable vertical propagation. SPW ðs ¼ 2Þ varies less with the dust load, dissipates lower, and contributes to the warming only below @ 0.1 mb. Transient planetary wave (s ¼ 1, period @ 5 sols) with a barotropic/baroclinic vertical structure provides up to 1/3 of the forcing by SPW ðs ¼ 1Þ. For the first time, we demonstrated a significance of small-scale gravity waves and eddies in maintaining the meridional circulation in Martian middle atmosphere, at least in high winter latitudes during dust storms.