Abstract
A possible circulation feature of thermal convection in the Martian lower atmosphere driven by radiative heating is investigated by the use of a two-dimensional anelastic model. Two cases of numerical simulations are performed; convection without dust and convection allowing dust injection from the surface by convective wind. The results of the simulations reveal that the thermal convection in the Martian lower atmosphere is km-size convection; the maximum vertical and horizontal scales of convective cells are 10 km and 5 km, respectively. In the case of dust-free condition, the values of both horizontal and vertical wind velocity often exceed 20 m see. The instantaneous maximum value of the surface stress associated with the km-size thermal convection reaches 0.04 Pa, which is equal to the threshold value to raise dust from the surface obtained experimentally. This result indicates that, the Martian general circulation models (GCMs), which have not been able to inject dust into the atmosphere, are now expected to simulate dust injection and the occurrence of global dust storm self-consistently by parameterizing the surface stress contribution associated with the km-size thermal convection. When dust is allowed to be injected into the atmosphere, dust spreads into the convective layer promptly and is well mixed within a few hours. After dust reaches the stratosphere, the depth of the convection layer becomes shallower and the intensity of convetive wind becomes smaller than those of the dust-free case. This is because the stratospheric temperature increases due to the absorption of solar radiation by dust.
