The Global Mars Multiscale Model: A tool for simulation of climate and weather

The present work presents a new three dimensional model for the Martian atmosphere and several application studies that highlight its performance and give some attempts to understand various aspects of the atmosphere of Mars. The dynamical core of the model, that deals with numerically solving the Navier-Stokes equations, has been adapted from the operational weather forecast model used in the Meteorological Service of Canada. The adapted grid-point dynamical core allows the definition of a region of variable horizontal resolution using a zooming system and hence the ability to conduct mesoscale simulations over areas of interest. Such mesoscale studies are usually performed using limited area models. The time resolution method is semi-implicit and the advection scheme is semi-Lagrangian, both characteristics allow moderate time-steps to be used and high resolutions to be specified without affecting the stability of the model. The model uses the topography measured by the Mars Orbiter Laser Altimeter and the surface radiative properties measured by the Thermal Emission Spectrometer, both instruments are aboard the Mars Global Surveyor spacecraft launched to Mars in 1996. The model's vertical extent covers the atmosphere from the surface to 160-180 km. At present, the atmosphere's composition is currently held constant and the total mass is constant during simulations. A new comprehensive radiative scheme has been developed and appended to the model to calculate the heating and cooling tendencies that result from Solar radiation and infra-red emission. The surface response to the radiative energy is obtained using a force-restore method. The convective activity in the turbulent boundary layer affects the large scale flow and an eddy diffusion parameterization gives the subgrid turbulent fluxes. Molecular diffusion becomes an important process in the low densities of the thermosphere, and thus thermal diffusion is included in the energy equation.; The evaluation of the model in its current state has revealed that it is a promising tool both in the uniform and zoomed configurations. The surface temperatures show the expected behavior regarding the diurnal variation and the changes related to the season and dust amount. The boundary layer profiles reflect the known features of the Martian boundary layer and the vertical profiles of temperature give a proper thermal structure. The zonal averages show a reasonable global meridional circulation and a good agreement with simulations from other models, especially in the mass streamfunction values that reflect the Hadley circulation. The agreement with the Thermal Emission Spectrometer temperature profiles is also encouraging. An important asset of this model is its ability to perform high resolution simulations over a limited area while remaining a global model. This feature has been tested in two cases: over Pavonis Mons which is the middle volcano of the Tharsis Montes volcanoes and in the Viking 1 landing site in the Chryse Planitia region. Both cases give satisfactory results. The simulated air flow near Pavonis Mons shows clearly the volcano's dynamical and thermal effects. The overall simulated meteorological conditions and the time series of the measurements made by the Viking instruments show a reasonable and encouraging accord.