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Y. Narumi (Kyushu-Tokai University)
During the winter season, the polar hood clouds cover the north polar region of Mars. The hood cloud is considered that it has some influence on the growth of the polar cap itself. We investigated the thermal effects of the polar hood on the heat budget of the atmosphere and surface of the polar region. The polar hood cloud is estimated to be composed of the water ice and/or dry ice (solid carbon dioxide) particles. We calculated the atmospheric and surface temperature distributions with various optical thickness of hood material. The results for the water ice model and dry ice model showed almost same thermal behavior. In both models, the daytime atmospheric and surface temperatures show very little change with increasing hood opacity because of little absorption of the solar radiation by the cloud particles. However, the nighttime surface temperatures increase with increasing hood opacity due to a greenhouse effect by the cloud particles. This property is very different from the thermal effect of the atmospheric dust. In the dust model, it was found that the daytime surface temperatures decreased with increasing opacity as less solar radiation reaches the surface. Thus, the seasonal polar hood may serve to retard the growth of the seasonal polar cap. Some terrestrial observers suggested that the north surface cap is only deposit at the vernal equinox (Iwasaki et al.1979), because of the appearance of some albedo features beneath the north polar hood clouds in red light. We hope to find a clue to explain the growth of the north polar cap through the investigation of thermal effect of the polar hood
The author(s) of this abstract have provided an email address for comments about the abstract: narumi@skk-1.ktokai-u.ac.jp