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題 名 | 中央氣象局全球模式之淺積雲參數法的改進=Improved Shallow Cumulus Processes in the Central Weather Bureau Global Forecast System |
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作 者 | 汪鳳如; 李瑞麟; | 書刊名 | 氣象學報 |
卷 期 | 44:4 2002.12[民91.12] |
頁 次 | 頁1-23 |
分類號 | 328.62 |
關鍵詞 | 淺積雲; 非局部混合; Shallow cumulus cloud; Nonlocal turbulent transfer; |
語 文 | 中文(Chinese) |
中文摘要 | 中央氣象局的全球作業模式經氣候模擬(Chen et al. 1999)診斷發現低層水氣傳輸不足,同時降水的分布有幾個明顯不合理處,例如夏季在西太平洋的副熱帶區有過多的大尺度降水,但在東太平洋的赤道區則是明顯低估深積雲降水。 淺積雲參數法是造成偏差的可能原因之一。本研究以此為研究方向,從一維測試著手,以BOMEX實驗資料測試作業版之淺積雲參數化,發現作業版之方法無法適當模擬淺積雲層。於是本研究引進Li(1994)所提出的方法,此方法不僅考慮了淺積雲內擴散混合係數的垂直變化,同時考慮了非局部的對流混合效應,因此新版之淺積雲參數方法在一維測試中,維持了與觀測較為接近的淺積雲層。 在進一步的三維模擬測試中,新版方法更考慮了環境的逸入對流可用位能(ECAPE)及雲層厚度等環境相關資訊來決定淺積雲混合係數;模擬結果顯示,無論是降水的分布、地面氣壓及地面通量,均有非常顯著的改進。 |
英文摘要 | It has been reported that the low-level horizontal water vapor transports were not sufficient in the CWB Global Forecast System (GFS) and the geographical patterns of precipitation rate were not well simulated by the GFS. These could be because the shallow cumulus processes are not well formulated in the model. Results from tests with a single-column version of the GFS indicate that the scheme fails to maintain observed shallow cumulus clouds in the planetary boundary layers during BOMEX. The scheme only considers local cumulus diffusion and ignores its vertical variations. In this study, we adopt a new scheme which is a simple eddy diffusive scheme with a nonlocal transfer inclusion. This scheme, developed by Li and Young (1994), represents the cumulus fluxes of liquid water potential temperature and total water as the sum of local diffusion plus nonlocal convection. The shallow cumulus cloud layer is well maintained for the BOMEX condition by the new scheme in the single-column tests, The 3-D results simulated using the new scheme but with a fully coupled version are very encouraging; the geographical distributions of July precipitation rates, sea level pressure and surface latent heat flux show more realistic patterns and values than those simulated by the current operational scheme of the GFS. |
本系統中英文摘要資訊取自各篇刊載內容。