Dune-forming winds on Titan and the influence of topography
Dune-forming winds on Titan and the influence of topography
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DOI：
10.1016/j.icarus.2007.10.007
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发表时间：
2008-03
期刊：
影响因子：
3.2
通讯作者：
T. Tokano
中科院分区：
文献类型：
--
作者：
T. Tokano
卡西尼雷达探测到土星卫星土卫六上许多延伸的沙丘限制了表面风的长期模式。我们分析了统计的地面风速和风向及其空间和时间的变化预测的大气环流模式（GCM），以约束地面风的预测，这GCM沙丘观测。该模型表明，现代风是足够的跃移和沙丘的形成在低纬度地区，在那里的沙丘的存在。沙丘形成风的最佳条件出现在0.02 m s− 1或更小的临界摩擦速度。由于高的沙粒漂移潜力和哈德利环流季节性逆转导致的斜向赤道的钝双峰风型的综合作用，赤道地区有利于纵向沙丘的形成。越赤道风是稳定的，其特征是高威布尔形状参数（k ≥ 4）。高纬度地区的风型更为复杂，阵风更大，无论是纵向沙丘还是横向沙丘都无法形成。假定的大尺度地形被发现有深远的影响近地面风模式。一般来说，山脉会在侧翼造成辐合和加速，而盆地则会减弱风并造成辐散流。纵向沙丘在山脚下可以偏转高达90°。如果Xanadu是一个假设的大山，风模式收敛在Xanadu，完全不同意的沙丘观测预测。如果元上都是一个大盆地，则风在元上都以北顺时针方向，在元上都以西和西南方向逆时针方向，与元上都附近的沙丘方向一致。对流型对风场的影响相对较小。孤立的山脉只造成局部尺度的风型变化。然而，持续的表面东风在贝莱德，这是在冲突的沙丘方向，不消失的任何组合的大尺度地形。
Numerous extended dunes on Saturn's moon Titan detected by the Cassini RADAR constrain the long-term pattern of surface winds. We analyse the statistics of surface wind speed and direction and their spatial and temporal variability predicted by a general circulation model (GCM) in order to constrain surface wind predictions of this GCM by dune observations. The model shows that modern winds are sufficient for saltation and dune formation at low latitudes, in agreement with the presence of dunes there. The best condition for the dune-forming wind occurs with a threshold friction speed of 0.02 m s−1or slightly less. The equatorial region is conducive to longitudinal dunes because of a combined effect of a high sand drift potential and obtuse bimodal wind pattern oblique to the equator caused by the seasonal reversal of the Hadley circulation. The cross-equatorial wind is steady, and is characterised by a high Weibull shape parameter (k∼4). The wind pattern at higher latitudes is more complex and gusty, and neither longitudinal nor transversal dunes would be able to form. Putative large-scale topography is found to have a profound influence on the near-surface wind pattern. Generally mountains cause a convergence and speeding up on the flank, while basins weaken the wind and cause a divergent flow. Longitudinal dunes can be deflected on the foot of mountains by up to 90°. If Xanadu is a hypothetical large mountain, a wind pattern converging in Xanadu that entirely disagrees with the dune observations is predicted. If instead Xanadu is a large basin, the wind arcs clockwise north of Xanadu and anti-clockwise west and southwest of Xanadu, in agreement with the dune orientations in the vicinity of Xanadu. The albedo pattern has comparatively little influence on the wind field. Isolated mountain chains cause only local-scale change in the wind pattern. However, the persistent surface easterlies in Belet, which are in conflict with the dune orientations, do not disappear by any combination of large-scale topography.