垂直風切環境中非理想渦旋結構變化–以2006年碧利斯與凱米颱風為例

何秋鋆(Chiou-Yun Her)

指導教授 ： 張隆男 ； 林沛練

國立中央大學/地球科學學院/大氣物理研究所/碩士(2007年)

摘要

過去已有許多探討環境水平風的垂直風切對熱帶氣旋影響的數值模擬研究結果，但大多為理想模擬，實際個案的探討較少。本文利用WRF (Weather Research and Forecasting model) 針對2006年降水結構明顯出現波數一不對稱之兩個颱風個案—碧利斯及凱米颱風進行3公里高解析度模擬。結合綜觀天氣分析與模式模擬，探討兩者受環境垂直風切影響的差異，並比較與過去學者研究結果之異同。
　　模擬結果顯示，WRF能掌握兩個颱風強度趨勢、環境風場變化特性以及降水不對稱等結構。碧利斯與凱米的模擬路徑與RSMC最佳路徑類似，誤差不超過經緯兩度。強度模擬結果也與觀測有相同的變化趨勢，皆隨時間增加而增強，雖然誤差在最後一小時已有11百帕，但兩者相對之強度仍如同實際情況，凱米較強、碧利斯稍弱。降水分布方面，模擬同樣能掌握風切下游的降水量皆高於上游之特性，但碧利斯的模擬降水量稍高於觀測，可能是碧利斯結果中颱風強度過強或模式物理不夠完整所造成。
　　與過去學者研究結果相同，碧利斯與凱米都出現與風切方向明顯相關之波數一不對稱結構，且回波最大值呈現氣旋式旋轉。雖然無法看出如同理想模擬中垂直風切明顯減弱颱風強度的特性，但模擬結果皆能顯現垂直風切對颱風所造成之影響。模擬後期，碧利斯與凱米的環境垂直風切皆快速增大，兩者在風切上游處的對流皆受到抑制，但相對於碧利斯，凱米的環流範圍較小，環境氣流之沉降作用造成凱米中心中低層明顯的增溫，這顯示熱帶氣旋環流半徑大小會造成兩者中心熱力結構受垂直風切影響程度的差異。

關鍵字

颱風 ； 垂直風切

並列摘要

A number of numerical modeling studies have focused on the effect of vertical wind shear on TC structure and intensity, but they mostly used idealized symmetric vortex in a sheared environment. In this study, the development of typhoons BILIS (2006) and KAEMI (2006) in environmental vertical wind shear is investigated using Weather Research and Forecasting model (WRF) with finest grid length of 3km and synoptic analysis, the impact of the vertical wind shear on these two typhoon cases will be examined and compared with the previous studies.
The result is shown that the simulated track is within 2° latitude–longitude of the RSMC best track at the end of the 2-day integration. The model also reproduces reasonably well on the hurricane intensity, intensity changes and asymmetries in precipitation. The simulated intensity is about 11hPa deeper in BILIS and 11hPa weaker in KAEMI, but same as observation, KAEMI is stronger than BILIS. The WRF also simulated the structure and evolution of precipitation very well. However, the simulated rainfall rate in BILIS is higher than observed, the errors are possible due to some deficiencies in the model physics and the simulated intensity was stronger than observed.
In agreement with earlier studies, BILIS and KAEMI quickly develop to wave number one asymmetries with upward motion and rainfall concentrated on the downshear side, and the maximum reflectivity rotate cyclonically.The storm continuously intensifies with the vertical shear during 2 days, this appears to contradict with the previous findings that the vertical shear tends to produce negative impact on the intensification of tropical cyclones. However, the effects of vertical wind shear on the development of convective asymmetry setructure are very obvious. On later simulated stage, the vertical wind shear of both cases increases fast, and inhibit the development of convective in the upshear side. When vertical shear tends to suppress cloud development of KAEMI in upshear side through descending inflow of air, the low and mid-level warming of KAEMI was more obvious than BILIS. It shows that warm core structure in the center of tropical storms is sensitive to storm size in the vertical wind shear environment.

並列關鍵字

vertical wind shear ； typhoon

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