Research of precipitaion on ancient-Mars

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Many fluvial features on Mars indicate active hydrologic cycle on ancient-Mars. In this study, we investigated a water cycle on an idealized planet by using a general circulation model and applied its results to ancient-Mars. Following results are obtained : 1. Three climate regimes are recognized : A.Frozen regime : when the surface temperature is below the freezing point all the year, the entire surface is covered by ice and the hydrologic cycle is essentially stoped due to very low temperature. B.Upright regime : when the summer temperature exceeds the freezing point and the inclination of the spin axis is smaller than the width of the Hadley cell, low latitude area is dried and no precipitation occurs. C.Oblique regime : when the surface temperature is higher than the freezing point and the inclination of the spin axis is larger than the width of the Hadley cell, precipitation occurs in the low latitude areas during summer and winter. 2. Present Mars is in the upright regime with its inclination 23-24 degrees. Ancient mars, however, could have large inclination as large as 60. Thus, Mars likely experienced transition among different climate regimes. In particular, in the oblique regime, summer temperature gets high, this suggests that the oblique regime coincides with the 'past warm and wet climate' on Mars. 3. Cold and wet Mars is unacceptable because in such a situation the surface is entirely covered by snow and 'snow ball Mars' appears.