Mathematics – Logic
Scientific paper
Aug 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000mpse.conf..148r&link_type=abstract
International Conference on Mars Polar Science and Exploration, p. 148
Mathematics
Logic
Ice, Mars (Planet), Mars Surface, Polar Regions, Water, Water Circulation, Hydrological Cycle, Atmospheric General Circulation Models, Dust, Vapor Phases, Simulation, Three Dimensional Models
Scientific paper
Exchange of water with the residual water ice cap at the northern pole is likely the primary mechanism controlling the water cycle and the global abundance of atmospheric water. The mechanics of this exchange lie in the mixing of water between the polar airmass immediately adjacent to the cap and the airmasses at lower latitudes. To date, the most detailed models of these transport processes have been undertaken with global three-dimensional models. However, such models are least valid in these regions due to the topology of their construction. For example in grid-point models, grid points evenly spaced in longitude become progressively more tightly packed in physical separation. This necessitates filtering of dynamical fields, which degrade and modify the circulation. Mesoscale models represent an improved tool with which to investigate the polar circulation. They are designed to simulate limited domains and can be arbitrarily centered, in this case on the pole, eliminating topological problems common to global models. The only previous mesoscale study of northern polar water transport is described by Siili et al., who examined aspects of cap edge water transport and localized water cold trapping. However, two-dimensional models, such as that used by Siili et al., are inherently of limited utility for modeling transport due to their inability to treat the true three-dimensional complexity of atmospheric mixing processes (which are of crucial importance even in the global models). We have adapted a fully three-dimensional mesoscale model to examine Martian polar water transport. The model and conversion are described by Toigo and Richardson. The model is based on the Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR) Mesoscale Model version five (MM5) and is fully adapted to Mars. The northern polar cap is represented by Mars Orbiter Laser Altimeter topography, and Viking Infrared Thermal Mapper albedo and thermal inertia as reprocessed by Vasavada et al. Water ice is prescribed to exist everywhere that the albedo is above a value of 0.4. Exchange of water between the surface and atmosphere is parameterized using the surface flux scheme. Water transport in the atmosphere is implemented using the MM5 advection and diffusion schemes. Exchange of water between the vapor and ice phases in the atmosphere is implemented assuming instantaneous conversion at saturation to and from fixed ice particle sizes. More detailed microphysics may be implemented in the near future. Boundary and initial conditions for the simulations, including the spatial varying fields of atmospheric dust and water are derived from General Circulation Model (GCM) simulations with the Geophysical Fluid Dynamics Laboratory (GFDL) Mars GCM. We will present results comparing the transport fluxes of water between the northern polar- and mid-latitudes as simulated by the Mars MM5 and Mars GCM. We will describe the dominant modes of atmospheric transport, and comment on the implications for the water cycle control picture described by Richardson and Wilson.
Richardson Mark I.
Toigo Anthony D.
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