The Role and Importance of Gravity Waves in the Mesosphere and Thermosphere of Mars

Abstract:

Gravity waves are generated in the lower Martian atmosphere by flow over topography, strong convection, and volatile instabilities of weather systems. Upward propagation and the resulting dissipation of gravity waves produce a substantial amount of momentum deposition and heating/cooling rates in the middle atmosphere (50-100 km) and above the mesopause (~100 km). These waves have horizontal wavelengths usually smaller than the conventional resolution of general circulation models (GCMs), and, thus, their effects have to be parameterized. Simulations with the Max Planck Institute Mars GCM using the interactively implemented nonlinear spectral parameterization have revealed a very important role of gravity waves in the dynamics of the middle and upper atmosphere of Mars. They close, and even reverse, the zonal jets, enhance the meridional circulation and middle atmosphere polar warmings, facilitate the formation of CO2 ice clouds, and modulate the upper atmospheric response to dust storms. Gravity wave-induced cooling is as strong in the mesosphere and thermosphere as the major radiative cooling mechanism - the radiative transfer in the IR bands of CO2 molecules, and can explain the observed temperatures in the lower thermosphere.