Stratospheric superrotation in the TitanWRF model
Stratospheric superrotation in the TitanWRF model
复制标题
TitanWRF 模型中的平流层超级旋转
DOI：
10.1016/j.icarus.2011.03.025
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发表时间：
2011
期刊：
影响因子：
3.2
通讯作者：
A. Toigo
中科院分区：
文献类型：
--
作者：
C. Newman;Christopher Lee;Y. Lian;M. Richardson;A. Toigo
TitanWRF大气环流模式模拟没有子网格尺度的动量水平扩散，大致产生了泰坦平流层中观察到的超旋转量。我们将这些结果与卡西尼-惠更斯测量土卫六的风和温度进行比较，并预测未来季节的温度和风。我们使用角动量和转换欧拉平均诊断表明，赤道超旋转产生的情景角动量“转移事件”在模型自旋，并保持类似的（但更短）的事件，一旦模型达到稳定状态。然后，我们使用波和正压不稳定性分析表明，这些传输事件产生的正压波，在低纬度地区，然后通过一个关键层向极地传播，从而加速低纬度地区，同时减速中高纬度急流在晚秋通过早春半球。最后，我们确定的主导波负责的角动量转移接近北方冬至在自旋和稳定状态。我们模拟的问题包括纬度温度梯度峰值和纬向风发生比卡西尼CIRS观测到的低60公里，并且在80公里左右的纬向风速没有减少，惠更斯观测到。虽然后者可能是由于瞬态效应（如重力波），前者表明，我们的低（约420公里）模式顶部是不利的影响附近的急流峰值的环流，和/或我们需要积极的烟雾传输，以正确地模拟加热速率，从而环流。未来的工作将包括运行具有更高顶部的模型，并包括霾颗粒尺寸分布的平流。
TitanWRF general circulation model simulations performed without sub-grid-scale horizontal diffusion of momentum produce roughly the observed amount of superrotation in Titan’s stratosphere. We compare these results to Cassini–Huygens measurements of Titan’s winds and temperatures, and predict temperature and winds at future seasons. We use angular momentum and transformed Eulerian mean diagnostics to show that equatorial superrotation is generated during episodic angular momentum ‘transfer events’ during model spin-up, and maintained by similar (yet shorter) events once the model has reached steady state. We then use wave and barotropic instability analysis to suggest that these transfer events are produced by barotropic waves, generated at low latitudes then propagating poleward through a critical layer, thus accelerating low latitudes while decelerating the mid-to-high latitude jet in the late fall through early spring hemisphere. Finally, we identify the dominant waves responsible for the transfers of angular momentum close to northern winter solstice during spin-up and at steady state. Problems with our simulations include peak latitudinal temperature gradients and zonal winds occurring ∼60 km lower than observed by Cassini CIRS, and no reduction in zonal wind speed around 80 km, as was observed by Huygens. While the latter may have been due to transient effects (e.g. gravity waves), the former suggests that our low (∼420 km) model top is adversely affecting the circulation near the jet peak, and/or that we require active haze transport in order to correctly model heating rates and thus the circulation. Future work will include running the model with a higher top, and including advection of a haze particle size distribution.