Martian Meso-/micro-scale Winds & Surface Energy Budget

Regional, diurnal and seasonal variations of surface temperature are particularly large on Mars. This is mostly due to the Martian surface remaining close to radiative equilibrium. Contrary to most terrestrial locations, contributions of sensible heat flux (i.e. conduction/convection exchanges between atmosphere and surface) to the surface energy budget [hereinafter SEB] are negligible on Mars owing to low atmospheric density and heat capacity (e.g. Figure 2 in Savijärvi and Kauhanen, 2008). This radiative control of surface temperature is a key characteristic of the Martian environment and has crucial consequences on the the Martian geology, meteorology, exobiology, etc. In order to identify the impact of this Martian peculiarity to near-surface regional-to-local atmospheric circulations, we employ our recently-built Martian limitedarea meteorological model (Spiga and Forget, 2009). We use horizontal resolutions adapted to the dynamical phenomena we aim to resolve: from several tens of kilometers to compute regional winds (mesoscale simulations) to several tens of meters to compute atmospheric boundary-layer winds (microscale or turbulentresolving simulations, also called Large-Eddy Simulations, LES). Our discussions herein focus on the contribution to surface energy budget of sensible heat flux, which couples atmospheric temperature, surface temperature and near-surface winds. We show that, while daytime boundary layer convection indicates the prominence of radiative forcing over sensible flux over flat terrains (Spiga et al., 2010, and first section of this abstract), this is no longer true over slopes, as e.g. nighttime katabatic winds can cause sensible heat flux to become comparable to radiative flux (Spiga et al., 2011, and second section of this abstract). The contribution of sensible heat flux to the surface energy budget has been overlooked thus far: the Martian surface and atmosphere are more coupled than hitherto thought.