Yoshiyuki Takahashi

Topographically induced north‐south asymmetry of the meridional circulation in the Martian atmosphere

[1]xa0A Martian atmospheric general circulation model is developed to investigate the effect of topographic elevation in the meridional circulation of the Martian atmosphere. It is confirmed that, even at equinoxes, the meridional circulation below ∼20 km altitude has an asymmetric pattern with respect to the equator. Sensitivity experiments reveal that the topographic elevation difference between the northern and southern hemispheres is the most dominant factor for producing such an asymmetric circulation. Contributions from variations of surface thermal inertia and surface albedo are weak compared with that of surface elevation. Thermal budget analyses show that the mean meridional circulation below ∼20 km altitude is driven by convective heating whose magnitude is controlled by the potential temperature of the surface mixed layer. Since the Martian atmosphere is optically and thermally thin, the potential temperature of the surface mixed layer is directly influenced by the geometric height of the surface. The elevated southern hemisphere induces the upward motion of the Martian Hadley circulation to be located in the southern hemisphere even at equinoxes when the surface temperature distribution is symmetric with respect to the equator. At southern summer solstice, when the potential temperature of the southern surface mixed layer is highest, the convective activity there becomes most active, and thus the Martian Hadley circulation becomes most intensive. This seasonal intensification of the convective activity and the Hadley circulation may account for the frequent occurrence of dust loading in the summer southern hemisphere.