半隱式半拉格朗日法在雲模式中的應用

Application of Semi-Implicit Semi-Lagragian(SISL) Method to a Two-dimqensional, Slab-symmetric Cloud Model

郭廷新(Ting-Hsin Kuo) ； 曾忠一(Chung-Yi Tseng)

《大氣科學》 22卷3期 (1994/09) Pp. 387-416

摘要

本研究的主旨是將半隱式半拉格朗日法應用到二維可壓縮的平板對稱雲模式之中，希望通過半隱式半拉格朗日法優異的表現來改善模式的效率和解析度。雲模式採用Lin et al.（1983）的雲微物理參數化格式，考慮六種水質，其中有冰晶、雪和冰雹三種冰相質點。為了防止過飽和的發生，在模式中採用Tao et al.（1989）的非疊代冰水飽和調整技術。數值模擬分成三個實驗來進行，研究結果表明，風切對積雲的結構和演變有很重要的影響，在有垂直風切的環境條件下會導致傾斜的上升氣流，使得上升氣流中的降水質點能夠落出上升氣流，不會因為降水質點的拖曳作用而減弱了上升氣流的正浮力，維持穩定持久的對流運動。傾斜的上升氣流伴隨強烈的降水過程和特殊的降水結構引發強盛的下沉氣流，這種冷空氣下沉、外流造成密度流的特性，在陣風鋒面前緣舉升暖濕空氣引發了新胞的生成。模擬實驗也表明，並不是有風切存在的環境條件下就會有這種現象發生。

關鍵字

半隱式半拉格朗日法 ； 雲模式

並列摘要

In this study, we try to apply the SISL method to a two-dimensional, slab-symmetric cloud model. With the elegant performance of SISL method, the efficiency and resolution can be definitely improved. Within this model, we adopt cloud physics parameterization scheme of Lin et al. (1983) to include three kinds of ice particles. To prevent over-saturation, non-iterative ice-water saturation adjustment techniques of Tao et al. (1989) are used. Model outputs show that vertical wind shear is critical to the structure and life cycle of a convective cloud. Under an environment with vertical shear, updraft will tend to tilt and hydrometeor contained in the updraft will precipitate without giving negative buoyancy to the updraft. In such a situation, the precipitation downdraft develops in the upshear side and will not cut off the low level moisture supply. The most important characteristic to be noted is that severe precipitation process and tilting updraft structure induce a strong downdraft which in turn leads to a density current and triggers a new cell in the leading edge of gust front where warm and moist air is lifted. Model results also show that wind shear is one of the environmental conditions needed to trigger a new cell.

並列關鍵字

Semi-implicit semi-lagragian method ； Cloud model