夏季白天斜坡地區低層輻合與垂直運動的數值探討－第二部份：環境風場的影響

A Numerical Study of Daytime Low Level Convergence and Vertical Velocity along Mountain Slope in Summer-Part II: The Influence of Environmental Wind

陳輝堂(Hui-Tang Chen) ； 陳景森(Ching-Sen Chen)

《大氣科學》 15卷2期 (1987/10) Pp. 165-178

摘要

本文主要的目的在利用二維地形座標的數值乾模式，來探討頭境風場對於由地表加熟，所引起的輻合場及垂直運動場的影響。如果整層風場皆吹東風，則在西面斜坡地因地表加熱所引起的上升風（向東），與環境風場的東風作用，在該地區會形成低層幅合以及垂直運動，此與Banta（1984，1986）觀測與模擬的結果相似。輻合區及垂直運動場會從斜坡地往西移至平地，這種移動的原因，是受到東風平流及水平混合的作用。在模擬3至4小時後，垂直速度可達1 m/s以上，如果有適當的水汽配合，在斜坡地上方的垂直速度場可以促進雲雨的生成與發展。另外，如果在前面所提到西面斜坡地的輻合區，看成是有降水發生的對流系統，假設降水後的再蒸發，可以產生冷卻降溫的作用，則這種降溫會在斜坡地形成局部的輻散區。在輻散區的東邊有局部上升風形成，阻止原先的輻合區往西移動；而在輻散區的西邊有向西的下沉風，推動新生的輻合區迅速地往西移動。

關鍵字

雲模擬 ； 斜坡 ； 輻合

並列摘要

The purpose of this study is to use a two-dimensional non-hydrostatic model in terrain following coordinate system to study the effect of environmental wind on low level convergence and vertical velocity induced by surface heating. If wind was from east, main low level convergence and vertical velocity was formed along west slope. This was due to the upslope wind induced by surface heating and environmental wind from east. This leeside convergence is similar to that mentioned by Banta (1984, 1986). The vertical velocity associated with leeside convergence moved toward west. The movement was largely influenced by the horizontal wind advection and mixing.If we assumed precipitation can be formed in the convergence zone, then the evaporation cooling could affect the convergence zone quite a lot. The locally upslope wind induced by the cooling effect on the east side of cooling zone can prevent the convergence zone moving toward west. The locally downslope wind on the west side of cooling zone can help convergence zone move toward west very quickly.

並列關鍵字

cloud simulation ； mountain slope ； convergence