對流系統受環境風場垂直風切影響之理想化值模擬研究

The Idealized Cloud-Scale Simulation: Effect of Vertical Wind Shear of Environmental Flow

黃小玲(Shiao-Ling Huang) ； 楊明仁(Ming-Jen Yang)

《華岡理科學報》 18期 (2001/05) Pp. 79-98

摘要

本研究使用Yang and Houze (1995)雲模式來探討對流系統受到環境風場垂直風切之影響。經由雲模式模擬各物理場（如μ、ν、w、θ、p、qv、qc及qr等）的演變，研究發現環境風場之垂直風切顯著影響對流系統的強度和其結構的變化。數值模擬實驗使用Weisman and Klemp (1982)的理想化探空曲線，且應用暖胞以激發對流的生成。數值實驗的控制變數為環境風場垂直風切，吾人考慮近地面2.5公里的垂直風切為5ms-1、10ms-1、15ms-1及20ms-1 情況，模擬在水平網域300公里範圍中對流系統在2小時內的發展、成熟及衰退情形。模擬結果顯示，不同的環境風場垂直風切將明顯改變對流系統的垂直速度強度、系統移動速度、系統傾斜情況及雲頂高度。數值實驗發現，近地面2.5公里之垂直風切在5～15ms-1的條件下，對流系統強度有隨著風切增加而逐漸增強的趨勢；但當近地面2.5公里之垂直風切大於15ms-1時，對流系統將受到水平風場的強烈拉扯而使得系統結構發展得不完整，此時系統發展強度則有減弱的趨勢。透過本理想化的數值模擬實驗，將可增進吾人對於對流系統強度及其結構受到環境風場垂直風切之影響程度的瞭解。

關鍵字

環境風場垂直風切 ； 對流系統

並列摘要

The Yang and Houze (1995) cloud model is used to investigate the effects upon convective systems by the vertical wind shear of environmental flow. Through the diagnostics of model outputs ( like μ、ν、w、θ、p、qv、qc and qr) from idealized numerical experiments, we find that the environmental wind shear strongly affects the intensity and evolution of simulated storm. The idealized sounding of Weisman and Klemp (1982) was used as the environmental profile for each experiment, and a warm bubble was used to initiate convection development. The vertical wind shear for each experiment is 5 ms-1, 10 ms-1, 15 ms-1, and 20 ms-1 at the lowest 2.5 km, respectively. The horizontal domain size is 300 km and the integration time is 2 hours. Numerical simulations show that the vertical wind shear significantly influences the updraft intensity, moving speed, vertical orientation, and cloud-top height of convective system. When the vertical wind shear is 5-15 ms-1 in lowest 2.5 km, the simulated storm increases its updraft intensity with increasing environmental wind shear; when the lower 2.5 km wind change is greater than 15ms-1, the simulated storm decreases its intensity with increasing wind shear. Based on the idealized numerical experiments, this study hopes to improve our understanding of the impacts of environmental wind shear upon the storm's evolution and structure change.

並列關鍵字

environmental wind shear ； convective system ； cloud model