利用CAA都卜勒雷達資料分析四個侵台颱風伴隨雨帶之特徵

An Analysis of Rainbands Associated with Four Landfalling Typhoons Using CAA Doppler Radar Data

李清勝(Cheng-Shang Lee) ； 蔡德攸(De-Lou Tsai)

《大氣科學》 23卷2期 (1995/06) Pp. 209-236

摘要

本文利用位於中正機場之民航局（CAA）都卜勒雷達的觀測資料，針對亞力士（1987）、莎拉（1989）、歐菲莉（1990）及楊希（1990）等四個颱風個案，分析颱風侵台時所伴隨雨帶之特徵，並初步探討地形對雨帶可能造成之影響。分析時，依雨帶出現的位置以及雷達資料所顯示的回波特性，將侵台颱風伴隨的雨帶歸納為六類，分別為出現於颱風前方的颱風外圍雨帶、在地形斜坡上近似滯留的地形雨帶、颱風登陸前於眼牆對流前緣生成的主要雨帶、位於颱風後方伴隨於西南氣流的雨帶、自眼牆周圍分離出的雨帶以及海上對流組織而成的雨帶。外圍雨帶、地形雨帶和海上對流組織成的雨帶具有明顯的胞狀對流回波型態；主要雨帶的回波在水平及垂直方向發展較為一致，較屬於層狀回波型態（Barnes et al., 1983）。伴隨西南氣流之雨帶其上游為胞狀回波結構，但下游則轉為層狀回波型態。至於自眼牆分離出的雨帶，剛分離時較具層狀回波型態，但隨著雨帶向外運動，漸轉成胞狀回波型態。分析結果顯示，地形雨帶乃因潮濕氣流受地形舉升而生成，其相對於颱風之位置及移動沒有明顯規律性；伴隨西南氣流的雨帶與西南氣流中的豐富水汽有關，故均出現於颱風後方。除上述兩種雨帶外，其他四種雨帶皆隨颱風旋轉或移動。外圍雨帶及其中對流胞之運動情形，和Anthes（1982）所示者相似。主要雨帶之生成和減弱，與其所處之地形關係密切，但在雨帶生成後，有較明顯往上游發展之情形。由海上零星對流組織成之雨帶，與其他雨帶多生成於眼牆對流附近的情形大不相同。雖然主要雨帶、自眼牆對流分離出之雨帶和海上對流組織成之雨帶等三類雨帶之生成過程明顯不同，但三者仍具有些相似之特性；因此，針對是否有共同之物理機制主導此三類雨帶之生成過程，值得未來進一步分析。

關鍵字

颱風 ； 颱風雨帶 ； 地形效應 ； 都卜勒雷達資料分析

並列摘要

This study used CAA Doppler radar data to study the characteristics of rainbands associated with Typhoons Alex (1987), Sarah (1989), Ofelia and Yancy (1990) when they were around Taiwan. The possible influence of Taiwan topography on rainbands was also discussed briefly. In this analysis, typhoon rainbands around Taiwan were classified into six categories according to the location and the radar reflectivity pattern of rainbands. These rainbands were outer rainband (located in front of typhoon center), terrain-induced (semi-stationary) rainband, principal rainband (originated at the front edge of eyewall convection before landfall), rainband embedded in the southwesterly, rainband separated from eyewall convection and rainband organized from scattered convections over ocean. The outer rainband, the terrain-induced rainband and the rainband organized from scattered convections had cellular reflectivity (or convective) structure (horizonal gradient of reflectivity=6-8 dB/km). The principal rainband had a stratiform reflectivity pattern (Barnes et al., 1983). The reflectivity pattern changed from cellular at the upstream side to stratiform at the downstream side for the rainband embedded in the southwesterly. For the rainband separated from eyewall convection, the reflectivity pattern changed from stratiform to cellular as the rainband moved outward.Results also showed that the terrain-induced rainband developed due to the topographical lifting of the warm and moist flow, its location thus was not closely related to the center position and the moving direction of typhoon. Except the terrain-induced rainband and the southwesterly-embedded rainband, the other four rainbands moved or rotated with respect to the moving typhoon center. The motions of the outer rainband and the convective cells embedded in the rainband appeared to be similar to those dipicted by Anthes (1982). The formation and decay of the principal rainband seemed to be influenced by the topography. However, the principal rainband revealed a upstream development trend after formation. The formation process of the rainband organized from scattered convections appeared to be different from other rainbands which formed near eyewall convection. Although the formation processes for principal rainband, the rainband separated from eyewall convection and the rainband organized from scattered convection were quite different, these three types of rainband still showed some similarities. Therefore, there seemed to be common physics which was responsible for the formation of these rainbands. Further study was thus highly desirable.

並列關鍵字

Typhoon ； Typhoon rainband ； Terrain effect ； Doppler radar data analysis