Description of a global Mars mesoscale meteorological model and an investigation of katabatic flow on mars

Abstract

The University of Auckland Global Mars Mesoscale Meteorological Model (GM4) is a numerical model of the Martian atmosphere that has been developed through the conversion of the Penn State University / National Center for Atmospheric Research fifth generation mesoscale model (MM5). This thesis describes the design and implementation of the GM4 model, then utilises it to investigate katabatic flow over Olympus Mons and Vallis Marineris. The model is initialized through the implementation of a 'base-state' atmosphere. Continual boundary condition input from a general circulation model is unnecessary as the global domains of the model are self consistent and form a continuous domain around the entire planet. At present, all other mesoscale models of the Martian atmosphere rely on a general circulation model for initial and boundary conditions. A description of the model and its basic underlying physical principles as applicable to the atmosphere of Mars is presented. Comparison between ASI/Met data collected from Mars Pathfinder during its 1997 mission and simulated conditions using GM4 is given. Diurnal temperature variation as predicted by the model shows very good correspondence with the measured surface data, to within 5 K for the majority of the diurnal cycle. Mars Viking I surface meteorological data is compared to the GM4 model, yielding similar results. To assess the vertical structure of the atmosphere, simulations have also been compared with Mars Global Surveyor Radio Science temperaturepressure profiles. As a further test for the model, various seasonal comparisons of surface and vertical atmospheric structure are performed with the European Space Agency AOPP/LMD Mars Climate Database. Agreement between the two models is reasonable, though polar regions are not very well represented by the GM4 model at present as polar ice cover is excluded. The model is used to investigate katabatic flow over two regions of exaggerated topography on Mars. Over the slopes of Olympus Mons a diurnal cycle consisting of strong nighttime katabatic flow and weaker daytime anabatic flow with spiral structure is predicted. Strong katabatic flow is predicted down the walls of the Vallis Marineris canyon system, reaching speeds up to 36 ms-1 (~130 kmh-1). These winds converge at the valley floor to produce a drainage flow out of the canyon network, which may be a mechanism that spawns Martian dust storms. High resolution observations of Vallis Marineris support these findings.