A New Large-Eddy Simulation Model for Simulating Air Flow and Warm Clouds Above Highly Complex Terrain. Part II: The Moist Model and its Application to Banner Clouds
A New Large-Eddy Simulation Model for Simulating Air Flow and Warm Clouds Above Highly Complex Terrain. Part II: The Moist Model and its Application to Banner Clouds
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DOI：
10.1007/s10546-009-9419-x
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发表时间：
2009-08
影响因子：
4.3
通讯作者：
D. Reinert;V. Wirth
中科院分区：
文献类型：
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作者：
D. Reinert;V. Wirth
第一部分介绍了一个新的大涡模拟（LES）模型的干燥版本，该模型专门用于模拟高度复杂地形上方的气流和云。在这里实施的水分物理描述和气象LES的湍流入流条件的产生提出了一种新的方法。作为一个典型的应用领域，新模式被应用于模拟金字塔形山峰下风向发展的旗云。横幅云主要是一种动力现象，并形成在陡峭的山峰的背风面作为一个结果，动态被迫背风坡流。由于极端地形引起的高度不对称流场，即使在湿度和温度水平均匀的初始条件下也可以形成旗帜云。因此，额外的背风水汽源、迎风面和背风面的不同气团或辐射效应都不是旗云形成的先决条件。旗帜云形成的概率随着障碍物高度和坡度的增加而增加，并且在第一近似下，与金字塔的方向无关。有和没有水分物理模拟表明，对于所选择的设置，水分是唯一的次要旗云动力学。潜热释放对背风坡上升气流的加强和相应的云的形成几乎可以忽略不计。尽管如此，水分物理学被证明是诱导一个类似偶极子的结构在垂直剖面的布伦特-Väisälä频率，这反过来又导致了适度增加背风湍流。
In Part I the dry version of a new large-eddy simulation (LES) model was presented that is specifically designed to simulate air flow and clouds above highly complex terrain. Here the implemented moisture physics are described and a new method for the generation of turbulent inflow conditions for meteorological LES is proposed. As a typical area of application the new model is applied to simulate banner clouds developing downwind of pyramidal mountain peaks. Banner clouds are shown to be primarily a dynamical phenomenon, and form in the lee of steep mountain peaks as a result of dynamically forced lee upslope flow. Due to the highly asymmetric flow field induced by the extreme orography, banner clouds can form even under horizontally homogeneous initial conditions regarding both moisture and temperature. Thus, additional leeward moisture sources, distinct air masses on both windward and leeward sides, or radiation effects are no prerequisite for banner-cloud formation. The probability of banner-cloud formation increases with increasing obstacle height and steepness and is, to a first approximation, independent of the pyramid’s orientation. Simulations with and without moisture physics reveal that, for the set-up chosen, moisture is of only secondary importance for banner-cloud dynamics. The reinforcement of lee upslope flow and corresponding cloud formation due to latent heat release turns out to be almost negligible. Nevertheless moisture physics are shown to induce a dipole-like structure in the vertical profile of the Brunt-Väisälä frequency, which in turn leads to a moderate increase in leeward turbulence.