侵台歐菲莉颱風（1990）之數值模擬

A Numerical Simulation of Typhoon Ofelia (1990) during Its Landfall on Taiwan

李清勝(Cheng-Shang Lee) ； 林慧娟(Hui-Chuan Lin)

《大氣科學》 27卷3期 (1999/09) Pp. 235-256

摘要

本研究使用NCAR/PSU MM5，以ECMWF全球經緯度網路分析資料為模式初始場，模擬1990年6月歐菲莉颱風（Ofelia）侵襲台灣之過程。雖然初始資料所解析的颱風中心位置與強度有一些的誤差，但模擬的路徑與觀測大致相似。當模式颱風由花蓮南南東方接近台灣地形時，背風面副中心的形成亦與觀測相符。結果同時顯示，颱風向西北西移近中央山脈時，受地形影響，中心隨高度往西南傾斜。受地形阻擋後之低層環流中心稍向北移後即消失，但山脈西側背風區同時出現環流中心且亦往北移動。俟東側原颱風環流中心消失後，山脈西側副環流中心即成颱風環流主中心且轉向西北移動，逐漸脫離地形影響。本研究亦進行不同測試實驗，探討不同時間初始場，積雲參數化法及台灣地形之影響。平均而言，各實驗之颱風移速皆明顯偏快，約為觀測值的二倍，可能是模式中環境駛流偏強與β效應過於顯著（颱風最大風速半徑與環流範圍過大）所致。敏感度測試結果顯示，模式對於初始場非常敏感；初始場中對颱風環流解析的些微差異，可能造成模式初始旋轉加速後的颱風結構有相當大的不同，進而影響模擬颱風之強度與路徑。積雲參數化的測試結果顯示，Grell法、Kain-Fritsch法與Betts-Miller法可得類似的模擬結果；Anthes-Kuo法所模擬的颱風不僅強度偏弱，降水也不同於其他三種積雲參數化方法所產生之環狀降水分布。地形影響的測試結果顯示，台灣地形的存在有使颱風在地形上游減速的趨勢，且可能亦有使路徑稍偏東之情形。

關鍵字

颱風 ； 颱風登陸

並列摘要

This study simulated Typhoon Ofelia during its landfall on Taiwan in June, 1990, using the NCAR/PSU MM5. This model employed ECMWF global analyses as its initial condition. Although the center position and the intensity of Ofelia as determined from ECMWF data differed from the observations, the model generally performed well in the track simulation. The observed lee-side secondary centers, while typhoon was approaching Hua-lien from the south southeastern direction, were also simulated reasonably well. Results also showed that the circulation center tilted southwestward with height when typhoon moved closed to the Central Mountain Range (CMR). The low level circulation center, after being blocked by the CMR moved northward and dissipated shortly after. At the same time, a circulation center formed on the western side of the CMR and also moved northward. This center then became the primary circulation center of typhoon and would change its moving direction toward the northwest when the circulation center on the eastern side of the CMR disappeared.Different sensitivity tests were performed in this study to investigate the effects of different model initial times, cumulus parameterization schemes and the Taiwan topography. On the average, the model typhoon moved at a speed twice as fast as the observed, which was likely due to the stronger environmental steering flow and the enhanced β -effect (caused by larger radius of maximum wind and typhoon size) in the model. Result of sensitivity tests showed that model was very sensitive to the initial field. A small difference in the initial field might cause a large difference in the structure of typhoon vortex after initial spin-up, leading to different intensities and tracks of model typhoon. However, similar typhoon tracks and precipitation patterns were generated when Grell, Kain-Fritsch and Betts-Miller cumulus parameterization schemes were used. On the other hand, the Anthes-Kuo scheme appeared to produce a weaker typhoon with a different precipitation pattern. Results also showed that a reduction in the moving speed and a slightly eastward track deflection were evident as the typhoon encountered Taiwan topography.

並列關鍵字

Typhoon ； Typhoon Landfall