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Y. Narumi (Kyushu-Tokai University), K. Iwasaki (Kyoto Gakuen University)
During the southern springtime, the south polar cap retreats more rapidly in the polar region between longitudes 150W and 300W, compared with the other part of the southern polar region. The reason for this rapid retreat has remained enigmatic for a long time. Recently, Colaprete et al. (2005) proposed that the asymmetrical behavior of the south polar cap is caused by topographic forcing of atmospheric dynamics by the large basins, Argyre and Hellas. These results calculated by the Mars General Circulation Model (MGCM) may be correct on the large-scale phenomena of Mars. However, we would like to point out that this region of rapid retreat is almost coincident with the extent of the southern polar layered terrain, and propose that the polar layered terrain would play some distinct role in the asymmetrical retreat of the south polar cap. The north and south polar layered terrains are characterized by about 3 km of relief and are believed to be composed primarily of water ice mixed with dust. Because of the abundant amount of water ice, the thermal inertia of the polar layered terrain may be higher than the usual surface soil on Mars. Our preliminary model calculation shows that a higher value of thermal inertia results in less precipitation of the surface carbon dioxide ice. We expect that a higher value of thermal inertia for the polar layered terrain could explain the asymmetric retreat of the south polar cap, with its reduced quantity and delayed carbon dioxide ice deposit during winter, and earlier evaporation of ice in the southern springtime.
The author(s) of this abstract have provided an email address for comments about the abstract: ynarumi@ktmail.ktokai-u.ac.jp
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.