臺灣地區登陸颱風所伴隨之中尺度降雨特徵

Abstract

本研究使用中央氣象局劇烈天氣監測系統(QPESUMS)的雷達回波整合資料，分析自2004 至2007 年期間13 個侵台颱風降雨結構特徵在登陸前後的變化。將颱風的回波資料分別做軸對稱和非軸對稱的運算，進一步討論在不同颱風路徑、環境垂直風切、颱風移動速度、以及季節等因素下，颱風降雨結構的變化。 分析結果顯示：(1)路徑有打轉的颱風，其內核區(距中心100 公里以內區域)的降雨率在轉向前達最大值，隨後迅速遞減，因此在登陸時強度已減弱許多。而路徑無打轉的颱風其降雨率在登陸前大致上會遞增，在登陸時達最大值。碧利斯和梧提颱風由於結構鬆散情況例外。(2)環境垂直風切較大(850-200hPa≧7.5ms-1)的颱風，在垂直風切左側會有較強的降雨回波。而環境垂直風切較小的颱風，其 風切左右兩側之降雨分布較為對稱。弱風切條件下有幾個個案在內核區風切左側有較強回波，此與國外利用閃電和衛星資料的統計結果相當類似。(3)所有分析颱風在登陸前的移動速度皆大於5 ms-1，但是並無明顯最大回波集中在移動前緣的右側，此與過去海上之研究結果有所差異。(4)12 月份侵台之南瑪都颱風，外圍雨帶因與東北季風共伴而產生強回波，出海後因為東北季風較乾冷的空氣侵 入，使得颱風回波迅速消散。

Radar reflectivity data of QPESUMS system of Taiwan CWB is used to analyze changes in the rainfall structure of typhoons before and after landfall. This study covers 13 typhoons which made landfall on Taiwan from 2004 to 2007. Radar reflectivity data is averaged with axial symmetric and non-axial symmetric calculation. And changes in the rainfall structure of typhoon are discussed when typhoons were under different tracks, environmental vertical shear, translational speed, and seasons. The results indicate: (1) If the track of typhoon made loop before landfall, the rainfall rate in inner core (r<100km) of typhoon increases to maximum before making loop, and then decreases sharply. However, if the track of typhoon didn’t make loop before landfall, the rainfall rate increases to maximum at landfall. The rainfall structures of Typhoon Bilis and Wutip are scrappy and are the exceptions. (2) When the environmental vertical shear is strong (i.e., 850-200hPa≧7.5ms-1), the larger radar reflectivity will be found out the left-hand side of the vertical shear vector. When the shear is weak, the rainfall distribution is more symmetric. However, some typhoons when vertical shear is weak, there is larger radar reflectivity in left side of vertical shear vector in some typhoons. This result is rather similar with results compiled by using lightening and satellite data. (3) All the 13 cases, the translational speed is larger than 5 ms-1. However, there is not larger radar eflectivity in the front and right of motion vector. (4) Typhoon Nanmadol made landfall on Taiwan on December. The outer rainband of typhoon combining with northeasterly monsoon induced strong reflectivity. When Typhoon Nanmadol left Taiwan, reflectivity dissipated rapidly because of incursion of drier and colder air.