Physics
Scientific paper
Oct 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt.........3r&link_type=abstract
Thesis (PhD). UNIVERSITY OF CALIFORNIA, LOS ANGELES, Source DAI-B 60/04, p. 1652, Oct 1999, 303 pages.
Physics
Scientific paper
This study has focused on the development and application of the first fully three-dimensional model of the current Mars water cycle. Previous models of the water cycle have suggested the importance of transport processes in determining the observed variations in atmospheric water [Jakosky and Haberle (1992)]. This work addresses questions regarding the relative importance of water reservoirs, transport of water, control of global average vapour amounts, and the importance of clouds. The results of this work show that model transport out of the northern polar region during summer occurs primarily in surface forced, zonally asymmetric currents. Significantly more hemispheric transport is predicted than expected with zonal average models. Transport capacity is higher for south to north flow during southern summer than for north to south flow in northern summer. Houben et al. (1997) suggested that a model without regolith would ``flood'' with vapour. Our model does riot show this behaviour, thus the regolith may not provide sole control over global vapour amounts. The mechanism of ``equilibration'' for the model without regolith pivots on an annual average vapour flux balance across the northern high-latitude/polar latitude boundary. However, as there is always net loss to the south polar cold tap the ``equilibrium'' is only approximate. Simulations suggest that an exposed southern water cap would be unstable with respect to the northern cap. Comparison with zonal-average vapour data suggests that the residual cap provides <= 40% of the vapour observed to accrue after L S = 80°. Simulations employing seasonal ice show improved ``fits,'' but additional (regolith) sources are needed. As suggested by Kahn (1990), agreement with data requires cloud ice precipitation. Precipitation allows water to be removed from a cold atmosphere more rapidly than diffusion of ice or vapour. Simulations also suggest that cloud formation may reduce interhemispheric water transport [Clancy et al. (1996)]. The model evolution of zonal-average vapour distributions is in rough agreement with data. Cloudiness is generally overpredicted, likely due to defects in the cloud microphysics scheme. The spatial distribution of clouds compare reasonably well with the limited observations, however errors do occur in the tropics and winter hemisphere. These likely result from errors in the vertical wind field and local scale vapour transport. Differences between the true and model topography and surface temperatures are the most likely causes. Detailed modeling of vapour transport will require very close attention to the surface prescription.
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