A toy climate model for Mars

Abstract

A “toy climate model” TCM was constructed for Mars. It returns the midday surface and near-surface air temperatures, given the orbital parameters, season (Ls), latitude, thermal inertia, albedo, surface pressure and dust visible optical depth (τ). The TCM is based on the surface energy balance with radiation terms calibrated against line-by-line calculations and surface heat flux terms against 1D model simulations. The TCM air temperatures match various lander observations reasonably well, e.g. the 3.4 martian years of recovered T1.6m from Viking Lander 1.The results demonstrate strong sensitivity of Ts and T1.6m to the dust load. All the VL1 years suggest major dust storms around Ls 270–300°, while τ appears only moderate in the simultaneous VL2 observations. The TCM was further extended to increased surface pressures, using moist 1D simulations. The greenhouse warming remained modest and the diurnal range was small in a thick CO2 atmosphere. As the CO2 condensation temperature Tc increases rapidly with pressure, the range of afternoon temperatures at various latitudes remains quite narrow in a thick atmosphere. The TCM can also deal with orbital parameter variations. A high-eccentricity, high-obliquity case was demonstrated for the present 7mb (Tc 150K) and a 1bar CO2 atmosphere (Tc 195K). High obliquity of 45° led to quite wide winter polar ice caps, which extended down to the subtropics. In the 1bar case even the equatorial Ts was close to Tc at aphelion; a major dust storm at that time led to a tropical CO2 ice cover.