對流性雲街的數值模擬

冬季寒潮暴發時西太洋地區邊界層對流性雲街之形成，主要是因熱對流不穩定而產生的。本研究使用美國普渡大學中尺度數值模式探討大尺度冷平流效應及潛熱釋放對雲街的影響。此模式為一原始方程模式，包含了科氏力，水汽的蒸發與凝結，渦動造成的熱量與動量的傳送，及海面與大氣間的熱量、動量、及水汽交換，等物理過程。冷（乾）平流與暖海面造成的增溫（加濕）效果相抵消，使邊界層的結構與邊界層內對流的強度達到一準恆定狀態，同時邊界層內的對流有充分的時間發展。由於邊界層內的溫度不再增加，使得海水與低層空氣溫度差可以維持一較大值。此與實際觀測的情況較為吻合。潛熱釋放明顯地使對流的強度增加，並造成了上升運動與下降運動的不對稱性質。本文並探討了對流發生的水平尺度及渦動動能收支情形。

關鍵字

雲街；對流邊界層；數值模擬；冷平流；乾平流

並列摘要

Cloud streets, which are often found over the East China Sea during cold air outbreaks in the winter season, was simulated by utilizing a high-resolution numerical model. The model includes most of the major physical processes, such as, surface exchange of heat and moisture between water and air; condensation and evaporation; and vertical turbulent transfer of heat, moisture, and momentum. The purpose of this study is to investigate the effects of large-scale cold and dry advection, and latent heat release on the structure of those cloud streets.The heat (moisture) transported from the warm Kuroshio is taken away by the large-scale cold (dry) advection in the region. The convective boundary layer and the embedded cloud streets therefore reach a quasi-steady state. Strong shallow convection develops with air-sea temperature difference maintained at a high level. The convection is further enhanced by latent heat release, also asymmetry between the upward and downward branches of the convection is largely due to latent heat release. We also investigated the aspect ratios of the cloud streets and performed buget analyses for the turbulent kinetic energy.

並列關鍵字

cloud streets ； convective boundary layer ； numerical simulation ； cold advection ； dry advection

國際替代計量

對流性雲街的數值模擬

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