莫拉克颱風雷達觀測中尺度雨帶特徵

The Precipitation Characteristics of Typhoon Morakot (2009) from Radar Analyses

陳台琦(TaiChi Chen Wang) ； 唐玉霜(Yu-Shuang Tang) ； 魏志憲(Chih-Hsien Wei) ； 林沛練(Pay-Liam Lin) ； 廖宇慶(Yu-Chieng Liou) ； 張偉裕(Wei-Yu Chang) ； 周鑑本(Chien-Ben Chou) ； 紀博庭(Bo-Ting Ji) ； 林忠義(Chung-Yi Lin)

《大氣科學》 38卷1期 (2010/06) Pp. 39-61

摘要

莫拉克颱風造成嚴重的水災，在整個颱風侵襲台灣期間，全台氣象雷達網包括6部都卜勒雷達及4部偏極化雷達，均全程觀測此移動非常緩慢的颱風，從觀測結果顯示颱風本身的環流與西南氣流共伴，並受地形影響後產生了一個延時很長、近似滯留的降水系統，因此透過雷達網資料可以詳細分析此強降水事件之風雨分布，並進一步了解其內部雲物理、雲動力特徵及致災的原因。
從雷達觀測可以明顯的看到此颱風結構有非常明顯的不對稱性，與典型颱風眼牆、雨帶的概念模型有很大差異：颱風眼區對流相當的微弱；對流旺盛的主要雨帶在台灣巴士海峽近似滯留；最重要的是來自颱風環流由台灣海峽南下的西北風與西南氣流輻合產生的致災雨帶，在台灣西南部重複形成或滯留，並與地形作用造成高雄、嘉義及南投山區破紀錄的累積雨量。在本研究中，將莫拉克颱風雨帶分為四區，討論對流區與層狀區的分布與颱風雨帶概念模式的異同之處，並將莫拉克颱風降水特徵分為四個階段，著重討論在8月8日00-24時，在台灣西南部的雨帶特徵，例如：雨帶的新生及發展與風場的關連性，以及雨帶南北來回移動的情形等，除了利用反演的雙雷達風場分析，可以分析雨帶內的風場輻合及上升運動的特徵，另外還利用馬公偏極化參數資料，了解對流胞內部的微物理結構。

關鍵字

莫拉克颱風 ； 雷達

並列摘要

The record breaking torrential rainfall of typhoon Morakot (2009) had caused serious landslide, flooding and casualty in southern Taiwan. Under a weak steering environmental flow condition, the rather complicate scale interaction between the strong southwestern flow, the relatively large size typhoon circulation and the Taiwan topography may cause a phase locked precipitation pattern. The weather radar network which consists of six Doppler radars, and four dual polarization radars had observed this slow moving typhoon during the whole episode of its influence. The unique structure of this enormous precipitation system can be vividly illustrated from the reflectivity distribution and three dimensional Doppler synthesis wind field. The convection and wind near the eye wall were relatively weak comparing with the principal rain band near the Bashi strait. On the day of Aug. 8, a few strong west-east oriented rain bands near southwestern Taiwan repeatedly formed along the convergence zone of typhoon circulation and southwesterly. These rain bands evolved near the southern edge of the circulation core and propagated southward or oscillated between lat. 23.5° and 22.5°. Many hot towers were embedded in these rain bands moving quickly toward island.
These deep convection cells and the strong wind associated with the rain bands had caused the heaviest rainfall accumulation in the hazard mountain area. The vorticity and momentum budget studies together with thermodynamic retrievals of these rain bands may provide more understanding of the precipitation mechanisms. The polarimetric radar further provided the microphysical information of the convective and stratiform regions of these devastation rain bands.
The detailed 3-D Doppler synthesis wind field revealed that the typhoon northwest wind circulation in Taiwan strait encountered the southwestern flow to cause a strong convergence zone and form the rainband. Many fast moving hot towers were embedded in these rainband, very strong and persistent updraft may explain the long life time of these deep convections. These hot towers had casted their landfall and moved into mountain area like a train. The jet like flow associated the rainband may reach 40 m/sec at lower levels. These fast strands of wind also were a major source of the upslope enhancement of the convections along mountain slope and ridge.

並列關鍵字

Morakot Typhoon ； radar observation