賀伯颱風登陸期間結構之雙都卜勒雷達分析

The Structure of Typhoon Herb(1996) during its Landfall by the Dual Doppler Analysis

曾吉暉(Chi-Huei Tsengch) ； 陳台琦(Chen Tai-Chi Wang)

《大氣科學》 27卷4期 (1999/12) Pp. 295-318

摘要

1996年之賀伯颱風侵襲台灣，造成台灣近幾年來最嚴重的災害。本研究利用中正機場雷達及五分山雷達，對於介於登陸時的賀伯颱風進行雙都卜勒風場的初步合成分析，希望能夠對於賀伯颱風侵台時的結構特徵有進一步的瞭解。在進行初步合成的分析時間中，可以觀測到雨帶（rainband）、低回波區（low echo zone）、眼牆（eyewall）等主要結構。結果顯示其回波及風場與過去一些觀測有以下的一些不同現象：我們發現在距離眼牆比較遠的地方，空氣是呈均勻的圓弧形運動，而當越接近強回波區時，空氣會轉向成平行橢圓眼的方向的橢圓形運動。這樣的空氣流動情形在橢圓眼長軸的端點處會有最大的空氣轉向現象，同時也會造成很強的空氣輻合，強的空氣輻合造成強的上升運動及強烈的對流活動。若是在眼牆附近的空氣一直是保持這樣的運動情形，在橢圓眼長軸的兩端就會一直有較強的回波出現。同時我們也由壓力擾動場發現在長軸的端點也是壓力梯度最大的所在。另外，我們也發現在登陸後約半個小時裡，眼牆區最大水平風速減小的輻度並不大。並且在邊界層上之垂直方向上，水平風速也是由下向上遞減，與暖心結構所需的熱力風平衡相符。最後，上升運動區在強回波區的外緣，似乎顯示在2km以上高度時，徑向的內流是在強回波區的外緣即轉而向上。

關鍵字

雙都卜勒 ； 結構 ； 賀伯颱風

並列摘要

Typhoon Herb(1996) had caused tremendous damage in Taiwan. However while it swept through northern Taiwan, it encountered two weather radars, one ISS (integrated sounding system), and many surface stations and raingauges. These instruments provide us opportunities to study the detail structure of Herb. Six contiguous dual Doppler radar syntheses and dynamic retrievals near landfall were carefully analyzed, the three dimensional wind and rain distribution patterns were clearly revealed. In the dual Doppler analysis domain we are able to observe the principal rainband, eyewall and the low echo intermediate region between the rainband and eyewall. Generally the overall structure are very similar to the hurricane structure observed in the literature.From the center of Typhoon along the radial direction outward, we observed three tangential wind maxima at four km height level, near the inner rim of eyewall, the first rainband and the second rainband. This secondary wind maximum phenomena were found at lower and middle levels. The pressure retrieval results indicated the local pressure minimums were also associated with stronger convection along the rainband. The pressure gradient force may partially explain the strong secondary wind maximum near the rainband. The kinematic flow pattern near the oval eyewall shown the wind actually blew parallel along the oval shape, while the flow in the low echo region, the wind pattern were circular. Hence near the tips in the long axis of the oval eye, the wind field became convergent. The stronger convection were persistent in these area are very reasonable.The 3-D wind structure analysis also revealed the horizontal wind speed near the eye wall has only decreased about 15%. The wind still agree with the thermo wind balance, horizontal decreased upward, this condition indicate the wind share, but, near the weak echo region/lower wind speed region, the wind share is reversed at lower levels. Hence the spin down processes is quite complicate, the further thermodynamic retreaval and momentum budget need to be studied for the mechanism.

並列關鍵字

Dual Doppler radar ； Structure ； Typhoon Herb