颱風環境下台灣東部沿海的對流線之觀測研究

本研究選取在蘇迪勒(Soudelor)、辛樂克(Sinlaku)、哈格比(Hagupit)颱風的環境下生成於台灣附近的線狀對流作為研究個案，分別稱之為RSOU 、RSIN 和RHA，並利用中央氣象局的五分山(RCWF)、花蓮(RCHL)、墾丁(RCKT)雷達、局屬測站地面觀測資料，空軍氣象聯隊的綠島雷達以及日本氣象廳與那國島的地面觀測資料來分析三個研究個案(RSOU、RSIN、RHA)，透過雙都卜勒雷達風場反演來檢視對流線內部的降水結構與三維運動場之特性，並與颮線的結構特徵作比較。個案發生時大環境主要受到颱風外圍環流影響，而沿岸風場的分析結果顯示離岸風(向岸風)沒有明顯日夜變化的特徵。另外，在日本石垣島一帶有高對流可用位能(CAPE)區，此區域與對流線的生成區一致，有利激發或維持對流，且對流線在靠近台灣近岸附近時逐漸減弱，此情形也與CAPE在近岸較小的分佈一致。另一方面，對流線向台灣東岸靠近的過程中，台灣東部沿海的高壓脊也會隨之加深，並隨著對流線的消散而減弱。由雙都卜勒分析顯示RHA、RSIN、RSOU的結構特徵皆具有其獨特性。三個對流線的降水回波結構，主要都為對流降水，無層狀降水區。而內部氣流結構也有所差異。RHA內為單一氣流結構，FTR(front-to-rear flow)在深對流區舉升。RSIN則出現了兩種不同的氣流結構，分別是FTR在深對流區舉升和RTF(rear-to-front flow)在深對流區舉升。R SOU 的氣流結構則與前兩個個案不同，為 FTR和RTF 兩支氣流在深對流區輻合舉升，此結構與先前研究的颮線結構有些類似。從垂直速度來看，伴隨RSOU、RSIN、RHA的最大垂直速度(~2 ms-1)遠小於颮線的典型垂直速度(~10 ms-1)。而在RSOU、RSIN通過地面測站後發現擾動氣壓以及垂直於線狀對流的氣流速度變化具有類似重力波的特徵，RHA則沒有。我們將內重力波與慣性重力波的相位速度與所研究個案之對流線移速相比較後發現兩者並不一致。

關鍵字

台灣東部沿海；線狀對流；颱風環境；颮線；台灣雨帶

並列摘要

This study investigates convective lines developing around Taiwan under the environment of Typhoon Soudelor, Sinlaku, and Hagupit using radar data from Wufenshan (WFS), Hualien (RCHL), Kenting (RCKT), and surface observations from Central Weather Bureau and Green Island radar of the Air Force Weather Wing, and Yonaguni surface observations of Japan Meteorological Agency. This research analyzes the three-dimensional characteristics of the precipitation structure in the convective line through dual-Doppler analysis for the three cases(RSOU, RSIN, RHA)and compared with the structure of squall line. For the cases study, the large environment are affected mainly by the typhoon’s outer circulations when the convective lines develop. Coastal wind analyes show no obvious diurnal variation in offshore flow(onshore flow). Furthermore, the area of high Convective Available Potential Energy (CAPE) near Ishigaki Island, Japan matches the generation area of the convective lines. There convective lines weaken near the coast of Taiwan, consistent with characteristic of smaller CAPE near the shore. On the other hand, the pressure ridge along the eastern Taiwan deepens as the convective lines approach the eastern coast of Taiwan, and weaken as the convective lines dissipate. The dual-Doppler radar analysis shows unique characteristics for each case. All three convective lines have convective precipitation without obvious stratiform precipitation. The internal kinematic circulations are also different. For R HA , the convective zone is dominated by Front-to-rear (FTR) flow that is lifted over the region of heavy precipitation. There is only a deep layer of either FTR or rear-to-front (RTF) flow lifted in the convective zone of R SIN . However, FTR and RTF converge in the convective zone for RSOU , an air flow pattern similar to squall-line’s structure documented previously.However, the maximum vertical velocities associated with RSOU , RSIN , RHA(~2 ms-1) are much smaller than the typical vertical velocity of squall line (~10 m s -1 ). During the passage of the R SOU and R SIN , the surface perturbation pressure(P’) and cross-band wind(Vc) show the feature of the gravity wave, whereas there is no obvious wave characteristic in the P’ and Vc for R HA . After comparing the phase speeds of internal and inertia gravity waves with the cases, it can be concluded that the two are not identical.