Exchange of water vapor between the atmosphere and surface
A model for exchange of water from the atmosphere to condensing CO2 caps is developed. The rate of water condensation in the caps is assumed to be propor-tional to the meridional heat flux. It follows that the amount of water condensed in the caps varies inversely with the amount of CO2 condensed. T...
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| Format: | Text |
| Language: | English |
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1973
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.535.4504 http://www.mars.asu.edu/christensen/classdocs/Leovy_ExchangeWater_icarus_73.pdf |
| Summary: | A model for exchange of water from the atmosphere to condensing CO2 caps is developed. The rate of water condensation in the caps is assumed to be propor-tional to the meridional heat flux. It follows that the amount of water condensed in the caps varies inversely with the amount of CO2 condensed. The seasonal phase of the release of water from the caps is not consistent with observed varia-tions in the abundance of atmospheric water. Seasonal variations of atmospheric water abundance are most consistent with vapor exchange between the atmosphere and permafrost in the subtropics. Although water condensation in semipermanent caps is normally very slow, it may take place at a much faster rate at unusually high atmospheric temperatures, such as those produced by absorption of solar radiation by airborne dust. The behavior of water vapor on Mars is likely to be an important key to under-standing the evolution of both the surface and atmosphere of the planet. Escape of hydrogen, presumably resulting from the photodissociation of water, has been ob-served (Anderson and Hord, 1971) and a plausible explanation for an equivalent rate of loss of the oxygen produced has been proposed (McElroy, 1972). The equivalent depth of water loss, if extended over 4 2 log years, amounts to 2-3m and is quite consistent with the observed amount of CO, in the atmosphere, if it is assumed that the ratio of H,O to CO, outgassed on Mars is about the same as that on the Earth (McElroy, 1972). On the other hand, it is quite possible that considerable water may be stored as permafrost, and both water and CO, may be permanently stored in the polar regions. The transfer of water to and from the polar caps has been considered by Leighton and Murray (1966) on the basis of a random walk model of meridional transport, with a fixed time constant of 5 days for the local removal rate. They concluded that the annual storage in the polar cap should be very small, amounting to only about 40g/cm2 over the precessional cycle (“5 x IO4 years). This ... |
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