A general circulation model with geography constrained by Cassini is used to predict how ethane precipitation in Titan’s lower stratosphere varies with latitude, season, and orbital forcing over the past 100 kyr. Ethane precipitation is generally more prevalent near the winter pole, where stratospheric ethane is transported downward toward the cold trap, and this general pattern is relatively insensitive to orbital parameter variations and geography. However, eccentricity-driven seasonal temperature variations modulate the seasonal asymmetry of ethane precipitation to some extent. The annual ethane precipitation does not monotonically increase from equator to pole but maximizes at selected sites, preferentially over empty deep basins such as Hagal Planitia. Local enhancement of ethane precipitation is caused by katabatic winds from plateau to basin and an associated regional-scale thermally direct circulation over the slope, which induces strong adiabatic cooling near the tropopause. The observed putative ethane clouds off the poles are evidence that ethane condensation is affected by topography. Preferential ethane precipitation over basins may increase the irregularity of Titan’s shape by isostatic crustal subsidence after substitution of enclathrated methane by percolated ethane.

地理环境受卡西尼号约束的一般环流模型用于预测泰坦平流层下部的乙烷降水如何随纬度、季节和过去 100 kyr 的轨道强迫而变化。乙烷降水通常在冬季极点附近更为普遍，在那里平流层乙烷向下输送到冷阱，这种一般模式对轨道参数变化和地理相对不敏感。然而，偏心率驱动的季节性温度变化在一定程度上调节了乙烷降水的季节性不对称性。每年的乙烷降水量不会从赤道到极地单调增加，而是在选定的地点最大化，尤其是在空的深盆地，如 Hagal Planitia。乙烷降水的局部增强是由从高原到盆地的衰减风和斜坡上相关区域尺度的热直接环流引起的，这导致了对流层顶附近的强烈绝热冷却。观察到的推定的极地乙烷云是乙烷凝结受地形影响的证据。盆地上的优先乙烷沉淀可能会增加泰坦形状的不规则性，这是在用渗滤的乙烷替代包裹的甲烷后的均衡地壳下沉。