Thermodynamic simulation of the seasonal cycle of temperature, pressure and ice caps on Mars

Abstract

We present a thermodynamic model to simulate the atmospheric temperature and pressure, the regolith temperature and the polar CO₂ ice caps vertical thickness and horizontal extent of Mars. This is done using the temperatures of the atmosphere and regolith for each Martian day of the year, determined from the thermodynamic equation. Assuming a CO₂ atmosphere, we calculate its emission spectrum using the spectral calculator E-Trans with the HITRAN database (E-Trans/HITRAN), resulting in only a band at 15 mm and the rest transparent, through which the radiation emitted by the regolith and ice caps (considered as black bodies) goes toward space. We also include the solar radiation extinction and longwave emission of atmospheric dust. The equation calculates the energy balance between the absorbed solar radiation and the outgoing longwave radiation, incorporating also the latent heat released by CO₂ condensation, the sensible heat flux from the surface to the atmosphere, the latent heat flux due to the CO₂ ice sublimation and the heat exchange between the surface regolith layer and its lower layers. The atmospheric planetary scale horizontal turbulent heat transport is parameterized with an exchange coefficient, which is an order of magnitude smaller than that employed in the terrestrial troposphere. Considering a long-time average, the regolith vertical temperature profile is explicitly found using the thermal inertia including conductivity; its temperature regulation is achieved through the thermal conduction from the surface during the warm season. This stored energy goes back to the surface during the cold season. Our model simulates the seasonal variation of the polar ice caps and consequently of the surface atmospheric pressure through the CO₂ mass balance between them. Finally, it is explicitly shown that the amplitude of the global seasonal pressure cycle is modulated by a local thermal-orographic effect, which increases (decreases) this amplitude in the low (high) regions, which agrees with the observations of the Viking Landers 1 and 2, and the Mars Climate Data Base. Our prediction for Hellas Planitia gives an amplification factor of up to 2.15, coinciding with other authors.