環境風場與風暴發展的數值研究

A Numerical of Storm Evolution in Different Wind Shear Environment

林熺閔(Shi-Ming Lin) ； 陳景森(Ching-Sen Chen)

《大氣科學》 11卷1期 (1984/03) Pp. 1-17

摘要

本論文是利用一個可壓縮的二維風暴數值模式，來研究風暴在不同的環境風場中的發展過程。其結果顯示，垂直風切造成上升氣流隨高度向下風切（downshear）方向傾斜。這種傾斜的上升氣流容易使降雨發生在上升氣流區以外的位置，不致阻碍上升氣流，而有助於風暴的發展。在低層約4公里以下的垂直風切造成風暴兩側陣風鋒面強度的差異。位於下風切方向的陣風鋒面有較強的水平輻合効應與上升速度，而相對於風暴的移動速度較慢。剛形成的陣風鋒面的抬升作用，在風暴附近所引發的新生雲胞與風暴合併時，可以使風暴的降雨與上升氣流加強。新生雲的發展過程在本文將有詳細的討論。同時利用診斷分析分別探討由動力項與浮力項造成的氣壓場對新生雲胞的貢獻，以便進一步了解風暴附近新雲的生成與發展過程。模擬結果顯示，在雲底附近有一個顯著的低壓區。在此分析過程中指出，這個底壓區的形成，並不完全是由浮力項造成的。由動力項造成的氣壓場對這個底壓區的中心位置與氣壓值也影響很大。

並列摘要

Using a two-dimensional compressible numerical model we investigated the evolution of storm in different wind shear environment. The tilting updraft along downshear direction resulted from environmental vertical wind shear. Rain could avoid of falling inside of the tilting updraft therefore storm would not be killed by rain easily. Gust front formed on both side of the storm due to the spread downdraft and the vertical windshear below 4 km height. Along the direction of downshear gust front had stronger horizontal convergence effect and induced vertical velocity than that on the other side of the mother storm. Clouds formed by the lifted effect of gust front could merge with mother storm which could intensify the strength of storm.The development of the formation new cloud along gust front will be discussed in this article. By diagnostic analysis we devided the effect of pressure fields into dynamic term and bouyant term. Simulation results showed that near cloud base there was a low pressure field which was not contributed by buoyant term completely. Indeed the intensity and position of the low pressure center affected by dynamic term to a large extent.