Research of precipitaion on ancient-Mars

火星上的许多河流特征表明古火星上有活跃的水文循环。在这项研究中，我们使用一般环流模型研究了理想行星上的水循环，并将其结果应用于古代火星。1.识别出三种气候状态：a.冰冻状态：当地表温度常年低于冰点时，整个地表被冰覆盖，由于温度很低，水文循环基本上停止。B.垂直形势：夏季气温超过冰点，自旋轴倾角小于哈德利环流宽度时，低纬地区干燥，无降水发生。C.斜压：当地面温度高于冰点，自旋轴倾角大于Hadley环流宽度时，夏季和冬季低纬地区发生降水。2.现今火星处于直立状态，倾角为23-24度。然而，古代火星的倾斜度可能高达60度。因此，火星可能经历了不同气候制度之间的过渡。特别是，在倾斜状态下，夏季温度变高，这表明倾斜状态与火星过去的温暖潮湿气候相吻合。3.寒冷潮湿的火星是不可接受的，因为在这种情况下，火星表面完全被雪覆盖，出现了雪球火星。

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.