Modeling of forced planetary waves in the Mars atmosphere

Graduation date: 1993Mariner 9 and Viking spacecraft observations during the 1970's have provided\ud evidence for planetary-scale wave-like disturbances in the Mars atmosphere. It has\ud been suggested that possible sources of the wave activity are dynamical instabilities\ud (e.g., barotropic and/or baroclinic instabilities). An other candidate source is forced,\ud quasi-stationary planetary waves. In connection with Mars' enormous relief, both\ud mechanical forcing and large-scale thermal contrasts due to spatially varying surface\ud thermal-inertia and albedo patterns should provide a strong source for planetary-wave\ud activity.\ud In this thesis, we attempt to model aspects of the observed wave activity, focusing\ud on forced planetary waves in the wintertime atmosphere of Mars. Our approach is\ud to apply two dynamical models: a linear primitive equations model and a quasi-linear\ud 'wave, mean-flow' model. Both models have spherical geometry and represent deviations\ud from zonal symmetry in terms of Fourier modes. The former model permits\ud a separation of responses to different elements that make up the total forcing mechanism,\ud whereas the latter is used principally to investigate the role forced planetary\ud waves may play in the Mars polar warming phenomenon.\ud Basic states representing relatively 'non-dusty' and 'highly dusty' conditions\ud near winter solstice allow wavenumber-1 and -2 disturbances to propagate meridionally\ud and vertically into the winter jet. Higher wavenumbers are strongly vertically\ud trapped. Stationary waves in the northern and southern extratropics differ strongly\ud in amplitude, phase and horizontal wave pattern.\ud The possibility for near-resonant, long-period modes in Mars' winter atmosphere\ud is also examined. For several wave-amplitude measures and dissipation strengths,\ud dusty low-frequency responses are an order of magnitude larger than non-dusty ones.\ud Wave, mean-flow simulations using wavenumber-1 or -2 forcings indicate north\ud polar warmings can occur for the dusty basic states. The sensitivity (magnitude, location,\ud and time scale) of a simulated warming to the wave forcing and the dissipation\ud strength is investigated