利用RAMS測試不同加熱作用對模式渦漩發展之影響

Testing the Influence of Different Heating Distributions on Model Vortex Development Using RAMS

李清勝(Cheng-Shang Lee) ； 簡國基(Gou-Ji Jian)

《大氣科學》 23卷1期 (1995/03) Pp. 93-122

摘要

本研究利用CSU-RAMS進行數值模擬，探討不同型態加熱作用對模式渦漩發展之影響。結果顯示，在本文模式架構下（1600公里×1600公里，40公里網格距）集中於模式中心附近之加熱作用，無法使模式渦漩形成眼，系統增強速率及加熱效率皆遠不及環狀分佈之加熱作用；結果亦印證颱風眼形成對渦漩後續發展的重要性（Malkus and Riehl, 1960）。由環狀熱源作用之模式渦漩演化，顯示系統在形成眼後，可進入Ooyama（1982）所指出物理決定階段（deterministic stage）。徑向分佈不同的環狀熱源模擬結果顯示，熱源分佈愈集中者，愈有利於模式渦漩眼的形成，但眼形成後，系統的發展速率與熱源的集中與否關係並不顯著。模式渦漩眼的形成過程為高層氣流於系統中心輻合，導致下沈增溫，此增暖作用隨積分時間逐漸向下延伸至低層，進而形成眼。垂直分佈不同的環狀熱源模擬結果顯示，由於模式渦漩熱力結構上的差異（即最大加熱高度較高者，所形成渦漩之最強暖心相對較高），使最大加熱高度愈高者愈有利於渦漩眼的形成；但當模式渦漩皆形成眼後，最大加熱高度較低者其氣旋式渦漩發展速率較快，且結構較緊密、紮實。不同緯度ｆ面測試結果顯示，渦漩切向風速之增加，以緯度高者較快，即原本針對中小尺度模擬而發展的RAMS，亦可合理表現科氏效應所導致之旋轉加速。本研究中，模式渦漩之發展情形因加熱型態與分佈之改變而有很大之變化，此結果與Hack and Schubert（1986）之結果非常類似。此外，模式渦漩眼的形成機制，與Arnold（1977）之診斷分析及Willoughbby（1979）之數值模式中所提出的論點相似；即在環狀熱源測試中，系統中心之無加熱區及加熱之徑向分佈，皆為造成中心下沈運動的主因；而系統中心下沈運動之垂直分佈（與加熱垂直分佈有關），與系統中心地面氣壓變化趨勢關係密切，且為影響眼形成快慢的重要因素。

關鍵字

模式渦漩發展 ； 數值模擬

並列摘要

This paper discussed the influence of different heating distribution on model vortex development based on the numerical simulations using CSU-RAMS. Results showed that no eye formed in a simulation with single heating forcing (maximized at the center) simulation under current model structure (1600 km × 1600 km, 40 km grid spacing). The model vortex formed an eye structure in the simulation with ring-type heating. The model vortex experienced faster development rate and the heating efficiency was higher especially after the formation of eye, for the simulation with ring-type heating. This result confirmed the importance of eye formation on the later development of model vortex (Malkus and Riehl, 1960). Current model simulations also supported that the model vortex entered the deterministic stage (as defined by Ooyama, 1982) after eye formation.Results of the ring-type heating simulation with different radial heating distribution showed that a radailly-concentrated heating was favorable to the formation of eye. However, the later development of model motex did not show much difference among different model simulations. The model eye formed as a result of subsidence warming due to upper level convergence. Results of the ring-type heating simulation with different vertical heating profile showed that model vortex eye formed faster when the maximum heating was placed at a higher level. It has to be noted that the maximum warm core ccurred at a higher level if the maximum heating was higher. However, after the eye formation, the model vortex with maximum heating at lower level experienced a faster spin-up in cyclonic circulation. The results also showed that the model vortex spun up faster if the model was placed at a higher latitude. In other words, RAMS can simulate reasonably the coriolis acceleration although it was designed for small scale simulation.Current model simulation showed that the development of model vortex was very sensitive to the type and distribution of heating as that of Hack and Schulbert (1986). The formation process revealed in this study agreed to that proposed by Arnold (1977) and Willoughby (1979). In the ring-type heating simulation, the radial heating distribution and zero heating at the center were important factors in producing the subsidence at the center. The vertical distribution of the sinking motion was related closed to the central surface pressure tendency and the timing of eye formation.

並列關鍵字

Model vortex development ； Numerical simulation