侵台颱風過山期間雨帶重建之初步研究

A Preliminary Study on Rainband Reorganization after Typhoon Moved across the Central Mountain Range of Taiwan

李清勝(Cheng-Sheng Lee) ； 鄭光浩(Kuang-Hao Cheng) ； 陳柏孚(Buo-Fu Chen) ； 謝宜桓(Yi-Huan Hsieh) ； 鄧旭峰(Hsu-Feng Teng)

《大氣科學》 43卷1期 (2015/03) Pp. 69-90

摘要

本研究利用中央氣象局之雷達回波合成圖，針對2005～2010年之13個西行且登陸台灣的颱風，以客觀方法計算選定強回波值面積在颱風內核區之比例，選取強回波（大於30 dBZ）比例在過山前後期間有減弱後再度增加者為雨帶重建個案；除分析雨帶重建颱風之綜觀特徵外，亦利用中尺度數值模式（WRF）模擬凡那比颱風（2010）侵台期間之雨帶重建過程，探討對流之變化及導致雨帶重建的原因。分析結果顯示，大部分雨帶重建颱風在接近台灣時尚處於增強階段，但未重建者則均處於減弱階段。此外，雨帶重建之颱風在侵台期間的平均移速較無重建者緩慢，尤其在颱風過山期間之差異最為明顯。利用NCEPFNL全球網格資料分析顯示，雨帶重建個案傾向發生在有較強之西南風、或西南風較弱但具有較強垂直風切的環境。分析模擬結果顯示，在凡那比颱風過山後雨帶重建過程中，西南氣流所夾帶之水氣以氣旋式方向繞過颱風中心，由颱風中心西側的北風環流攜入重建雨帶區，並與低相當位溫之環境沉降空氣在海峽南部會合，形成類似鋒面的結構。輻合區對流受偏北垂直風切影響，隨高度向南方傾斜，形成後方入流且伴隨前方層狀降水區（rear-fed leading stratiform）之中尺度對流系統結構特徵，而有利對流胞之持續形成，最終重新發展為有組織的雨帶結構。

關鍵字

颱風 ； 雨帶重建 ； 凡那比颱風（2010）

並列摘要

An objective methodology based on radar reflectivity images from the Central Weather Bureau was used to identify the reorganization of inner-core rainband for 13 westward-moving typhoons that affected Taiwan during 2005~2010. The ratio of the area with strong radar reflectivity (＞30 dBZ) to the total area for the inner core region was considered in the case selection procedure. Results show that most of the reorganization cases usually keep intensifying when they were approaching Taiwan, however all non-reorganization cases were during their decaying stage. Furthermore, the average westward component of translation speed of the reorganization case is lower than that of non-reorganization cases. Analyses of NCEP-FNL data show that the reorganization cases are located in an environment with stronger 850-hPa southwesterly flow or stronger 200-850 hPa vertical wind shear. The WRF model was used to simulate the rainband reorganization process of Typhoon Fanapi (2010) when it was affecting Taiwan. Analyses of the simulation results show that a frontal-type structure is analyzed at the rainband reorganization region. The high-�������� air to the north of the re-organized rainband is attributed to the moist air associated with the monsoon flow that moves cyclonically around the typhoon center, and the low-�������� air to the south of rainband is due to the mid-level environmental subsidence. Furthermore, because of the northerly vertical wind shear, the convections tilt southward with height which is similar to the characteristic structure of rear-fed leading stratiform mesoscale convective system. Such convective structure appears to be conducive to the continuous formation of convective cells leading to the reorganization of typhoon rainband.

並列關鍵字

Typhoon ； Rainband Reorganization ； WRF ； Typhoon Fanapi (2010)