The seasonal variation of Titans atmospheric structure with emphasis on thestratosphere is simulated by a three-dimensional general circulation model. The model includesthe transport of haze particles by the circulation. The likely pattern of meridional circulation isreconstructed by a comparison of simulated and observed haze and temperature distribution. TheGCM produces a weak zonal circulation with a small latitudinal temperature gradient, in conflictwith observation. The direct reason is found to be the excessive meridional circulation. Underuniformly distributed opacity sources, the model predicts a pair of symmetric Hadley cells nearthe equinox and a single global cell with the rising branch in the summer hemisphere belowabout z = 230 km and a thermally indirect cell above the direct cell near the solstice. Theinterhemispheric circulation transports haze particles from the summer to the winter hemisphere,causing a maximum haze opacity contrast near the solstice and a smaller contrast near theequinox, contrary to observation. On the other hand, if the GCM is run under modified coolingrate in order to account for the enhancement in nitriles and some hydrocarbons in the northernhemisphere near the vernal equinox, the meridional cell at the equinox becomes a single cell withrising motions in the autumn hemisphere. A more realistic haze opacity distribution can bereproduced at the equinox. However, a pure transport effect (without particle growth bymicrophysics, etc.) would not be able to cause the observed discontinuity of the global hazeopacity distribution at any location. The stratospheric temperature asymmetry can be explainedby a combination of asymmetric radiative heating rates and adiabatic heating due to verticalmotion within the thermally indirect cell. A seasonal variation of haze particle number density isunlikely to be responsible for this asymmetry. It is likely that a thermally indirect cell covers theupper portion of the main haze layer. An artificial damping of the meridional circulation enablesthe formation of high-latitude jets in the upper stratosphere and weaker equatorial superrotation.The latitudinal temperature distribution in the stratosphere is better reproduced.

中文翻译：

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大气环流模型模拟泰坦大气结构的季节变化

通过三维大气环流模型模拟了以平流层为重点的泰坦大气结构的季节性变化。该模型包括通过环流传输雾霾颗粒。通过比较模拟和观测的雾度和温度分布，重建了可能的经向环流模式。GCM 产生弱纬向环流，纬度温度梯度小，与观测相矛盾。直接原因被发现是过度的经向循环。不均匀分布的不透明源，该模型预测在春分点附近有一对对称的哈德雷单元和一个在夏半球低于 z = 230 公里处有上升分支的单一全球单元，以及在冬至附近直接单元上方的热间接单元。与观察结果相反，半球间环流将雾霾颗粒从夏季输送到冬季半球，导致冬至附近的雾霾不透明度对比度最大，春分点附近的对比度较小。另一方面，如果 GCM 在修改后的冷却速率下运行，以解决春分点附近北半球腈类和一些碳氢化合物的增加，则春分点处的子午线单元成为秋季半球上升运动的单个单元格。可以在春分点再现更真实的雾度不透明度分布。然而，纯粹的传输效应（没有微物理学等的粒子生长）将无法导致在任何位置观察到的全球雾度分布的不连续性。平流层温度不对称可以通过不对称辐射加热速率和由于间接热单元内的垂直运动引起的绝热加热的组合来解释。雾霾粒子数密度的季节性变化不太可能是造成这种不对称的原因。热间接单元很可能覆盖主雾层的上部。经向环流的人工阻尼使得在平流层上部形成高纬度急流和较弱的赤道超自转。更好地再现平流层中的纬度温度分布。热间接单元很可能覆盖主雾层的上部。经向环流的人工阻尼使得在平流层上部形成高纬度急流和较弱的赤道超自转。更好地再现平流层中的纬度温度分布。热间接单元很可能覆盖主雾层的上部。经向环流的人工阻尼使得在平流层上部形成高纬度急流和较弱的赤道超自转。更好地再现平流层中的纬度温度分布。