積雲參數化方法對MJO 肇始和傳播的影響;Impacts of Cumulus Schemes on the Initiation and Propagation of MJO

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题名:	積雲參數化方法對MJO 肇始和傳播的影響;Impacts of Cumulus Schemes on the Initiation and Propagation of MJO
作者:	張美玉;Chang, Mei-Yu
贡献者:	大氣科學學系
关键词:	季內震盪;積雲參數化方法;MJO;cumulus scheme
日期:	2019-08-21
上传时间:	2019-09-03 12:21:07 (UTC+8)
出版者:	國立中央大學
摘要:	利用中央氣象局全球預報模式偶合SIT海洋模式，選擇DYNAMO實驗期間2個主要MJO事件，探討不同積雲參數化方法，TDK法(Tiedtke 1989; Nordeng 1994)和SAS法(Simplified Arakawa-Schubert; Pan and Wu 1995; Han and Pan 2011) 對此期間MJO事件發生和傳播之影響。模擬結果顯示，TDK法在西赤道印度洋區域，可分別於15 天及45天前，預報MJO-1和MJO-2的發生；SAS法則否。診斷結果指出，TDK法可模擬出類似觀測的季節內尺度 OLR-SST (Outgoing Longwave Radiation-Surface Sea Temperature；外逸長波輻射¬-海溫)距平的演變關係，SAS法的預報則未能達此標準。探究其原因，在西赤道印度洋區MJO抑制期的海溫距平，主要受地表加熱通量的影響；海溫距平的變化，將引起邊界層的輻合及垂直上升運動，產生氣柱垂直積分的濕靜能正變化率，形成不穩定的大氣成層結構，進而激發對流的發展及MJO的發生。TDK法可成功模擬類似觀測的OLR-SST-濕靜能正變化率距平之演變關係；SAS法則否。另外，兩預報的傳播特性亦有明顯的差異，TDK法可模擬出MJO的東傳，SAS法則顯示西傳的預報；此歸因於TDK法可模擬出相對於MJO中心，氣柱垂直積分的濕靜能變化率具有正緯向梯度之觀測特性；SAS法所模擬的濕靜能變化率之緯向梯度特性則相反。預報差異的原因主要來自濕靜能垂直和水平平流距平的貢獻。 ;An operational weather forecast model, coupled to an oceanic model, was used to predict the initiation and propagation of two major MJO events during the DYNAMO campaign period. Two convective parameterization schemes were used to understand the sensitivity of the forecast to the model cumulus scheme. The first is the Tiedtke (TDK) scheme, and the second is the Simplified Arakawa-Schubert (SAS) scheme. The TDK scheme was able to forecast the MJO-1 and MJO-2 initiation at 15-day and 45-day lead, respectively, while the SAS scheme failed to predict the convection onset in the western equatorial Indian Ocean (WEIO). The diagnosis of the forecast results indicates that the successful prediction with the TDK scheme was attributed to the model capability to reproduce the observed intraseasonal OLR-SST relationship. On one hand, the SSTA over the WEIO was induced by surface heat flux anomalies associated with the preceding suppressed-phase MJO. The change of the SSTA, in turn, caused boundary layer convergence and ascending motion, which further induced a positive column-integrated moist static energy (MSE) tendency, setting up a convectively unstable stratification for MJO initiation. The forecast with the SAS scheme failed to reproduce the observed OLR-SST-MSE relation. The propagation characteristics differed markedly between the two forecasts. Pronounced eastward phase propagation in the TDK scheme is attributed to a positive zonal gradient of the MSE tendency relative to the MJO center, similar to the observed, whereas a reversed gradient appeared in the forecast with the SAS scheme with dominant westward propagation. The difference is primarily attributed to anomalous vertical and horizontal MSE advection.
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