「雙眼牆」颱風的探討

On Concentric Eyewall Typhoons

陳正改(Joe C. K. Chen)

《中華防災學刊》 7卷1期 (2015/02) Pp. 5-24

摘要

颱風或颶風等熱帶氣旋的「眼牆（eyewall）」，是最接近颱風中心（颱風眼）的環型對流雨帶；該區的風力最強勁，雨勢也最驚人。大部份的颱風通常只有一個「眼牆」，但發展成熟且強度達強烈階段的颱風也會出現「雙眼牆」（concentric eyewall）結構之特徵。根據氣象學者的研究文獻顯示，大西洋海域的颶風，至少有二分之一會出現「雙眼牆」現象，甚至還曾出現過「三道眼牆」（triple eyewall）的案例。但西北太平洋及南海海域的颱風具有「雙眼牆」特徵之案例，在過去則較罕見。然近年來，侵台颱風出現「雙眼牆」的案例竟時有所聞；此應歸功於我國都卜勒氣象雷達站網的建立、氣象衛星監測設備的更新，以及由學術界和氣象作業單位共同合作執行「追風計畫」（DOTSTAR），派遣飛機進入颱風暴風圈內蒐集大氣環境資料予以研判所致。這種「雙眼牆」結構到底是如何形成？又具有什麼科學意義？對我們的災害防救衝擊又是如何？本文擬針對近四十（1975~2014）年來於西北太平洋及南海海域所發生且對台灣地區造成嚴重災情，並具有科學研究價值的八個「雙眼牆」颱風案例作詳細回顧及探討，進而對其共同的特徵、結構和形成機制，加以分析及詮釋；藉此就教氣象界的先進們，同時與從事災害防救業務的所有師長和同仁們分享經驗及提供參考。

關鍵字

颱風 ； 颱風眼 ； 眼牆 ； 雙眼牆 ； 三道眼牆 ； 環型對流雨帶 ； 追風計畫

並列摘要

Eyewalls of Tropical cyclones (including typhoons and hurricanes) are rings of convective thunderstorms closest to eyes of cyclones. Most intense winds and torrential rainfall are perceived in eyewalls. Generally speaking, no more than one eyewall is observed in a tropical cyclone; however, concentric eyewall do appear in mature and tremendous cyclones. Previous studies indicate that at least one half of Atlantic hurricanes have concentric eyewall, even triple eyewall. However, typhoons with concentric eyewall are rather rarely perceived over the Western North Pacific and the South China Seas. Nevertheless, concentric eyewall has been recognized in several typhoons impacting Taiwan in recent years, a phenomenon which should be attributed to the construction of the national Doppler radar network, the renovation of satellite monitoring facilities, and the execution of the Dropwindsonde Observations for Typhoon Surveillance near the TAiwan Region (DOTSTAR) project, which incorporates the effort of academia and operational meteorological units and conducts observation by releasing dropsondes directly into typhoons. How does the concentric eyewall form? What is the scientific significance? How does this characteristic impact the disaster mitigation? The present article reviewed and investigated eight concentric eyewall typhoons over the Western North Pacific and the South China Seas which not only have significantly damaged Taiwan but also have appeared scientific significant. Common features, structure, and formation mechanisms were analyzed and interpreted so as to share experience and stimulate interaction and discussions from fellows specializing in disaster prevention and relief.

並列關鍵字

typhoon ； typhoon eye ； eyewall ； concentric eyewall ； triple eyewall ； a ring of convective thunderstorms ； Dropwindsonde Observations for Typhoon Surveillance near the TAiwan Region (DOTSTAR)