雙中尺度渦旋交互作用之初步模擬

A Preliminary Simulation on the Interactions between Two Mesoscale Vortices

李清勝(Cheng-Shang Lee) ； 朱昱璉(Yu-Lien Chu)

《大氣科學》 25卷4期 (1997/12) Pp. 547-568

摘要

觀測顯示，近赤道季風槽中的中尺度渦旋，有可能透過渦旋間的交互作用，發展為熱帶氣旋。本文為一初步研究結果，其目的在幫助了解此現象之物理過程。本研究使用CSU-RAMS模式，在不考慮環境強迫作用情況下，針對兩個強度相同之中尺度弱渦旋進行積分，初始渦旋之最大風速僅4m/s，有效半徑約100km，在f平面上進行積分，並考慮潛熱釋放效應（稱控制組實驗）。此外，亦進行測試實驗，以探討潛熱釋放、初始渦旋距離以及β效應的影響。控制組實驗結果顯示，積分過程中，兩個初始距離320公里之渦旋，反鐘向互旋且相互靠近（即所謂藤原效應）；然而，兩個原本強度相同之渦旋，亦逐漸產生一強一弱的情形，較弱的渦旋並逐漸變形成一狹長的渦度帶，捲入、合併至較強渦旋中。此外，於積分初期，渦旋因潛熱釋放效應而增強，隨後則持續減弱；其對流生命期類似熱帶積雲簇，測試實驗結果顯示：（1）不考慮水氣效應時，渦旋強度不會發展，且兩個渦旋一直維持相同強度；（2）渦旋互相靠近時，其垂直次環流結構不利於另一渦旋對流的發展，渦旋發展有明顯受抑制的情形；（3）β效應使合併後的渦旋往西北方向運動，且其發展的最大風速可達熱帶風暴的強度，遠大於其他組實驗。

關鍵字

颱風 ； 渦接交互作用

並列摘要

Observations showed that the meso-vortex embedded in the near-equatorial monsoon trough can develop into a tropical cyclone due to the interactions between vortices. To help understand the physics behind the vortex development, this preliminary study attempted to simulate the interactions between two weak mesoscale vortices without environmental forcing, using CSU-RAMS. The maximum wind speed of the initial model vortex was only 4m/s and the effective radius was about 100km. For the control experiment, the numerical integration was done on an f-plane with the effect of latent heat release being included. Besides the control experiment, several test experiments were done to study the effects of the latent heat release, the beta drift and the separation distance between the initial vortices.Results of the control experiment showed that the two vortices, separated by 320km initially, rotated counterclockwise and approached each other during the integration (or the so-called Fujiwara effect). The intensifies of these two vortices were the same initially, but started to differ from each other during the integration. The weaker vortex then deformed into a long narrow vorticity band and was wrapped into the stronger vortex. The intensifies of the vortices increased during the initial period of the integration due to the effect of the latent heat release. But the model vortices kept weakening after the initial developing period. The life cycle of the model vortex is comparable to that of a tropical cloud cluster. Results of the test runs showed that: (I) the two vortices always had the same intensifies during the integration without the effect of latent heat release. Also, both vortices did not intensify during the initial period. (II) When the two vortices moved closer to each other, the secondary circulation of one vortex was unfavorable to the development of the convection associated with the other vortex. The development of the model vortex thus was suppressed. (III) The beta effect caused the merged vortex to move northwestward. The merged vortex also developed to the tropical storm intensity, stronger than those of other experiments.

並列關鍵字

Typhoon ； Interaction of mesoscale vortices