台灣東部颱風湧浪預報的探討

Abstract

颱風波浪脫離暴風區域後稱為湧浪，常比颱風先到達岸邊，無預警的造成沿海的生命和財產的損失。梁(1989)提出颱風湧浪預報模式，然而在2006年艾維尼(Ewiniar)颱風的湧浪推算結果，與實測資料相差很遠，有必要重新檢討修正。本研究採用花蓮港波浪測站資料，結合中央氣象局颱風資料，求出湧浪週期的經驗公式為： Tp=(0.041667×A+0.1321)×UR4s A=(DD3×R4)/(TR4Br)^4 Tp其中為最大能量週期(秒)，DD3為颱風中心與花蓮港測站之間的距離(海浬)，R4為以Rodolfo法(2002)求出的最大風速半徑(公里，需轉換成海浬)，TR4Br、UR4s為停滯颱風以Bretschneider(1976) 颱風波浪推算法求出的最大風速半徑處的風浪週期(秒)及傾度風速(公里/小時)。 湧浪波高經驗公式為: Hs=0.2331×(HR4Br)×[√(R4/DD3)]×λ 其中Hs為示性波高(公尺)，HR4Br為滯留颱風以Bretschneider(1976)求出的最大風速半徑處的風浪波高(英呎)，λ為颱風接近或遠離測站時因為都卜勒效應(Liang，2003)而造成湧浪波高堆積或消散的修正係數。並以象神、碧利斯、科羅紗、辛樂克等颱風作驗証，均有不錯的結果。

As typhoon waves propagate out of the storm, it is called the swell. Since the group velocity of swell is swifter than the typhoon itself so that it often arrives shore earlier. Without warning the swell may cause serious property damage and even loss of human lives. Liang(1989) had proposed the typhoon swell forecast model. However, the swell hindcast for typhoon Ewiniar in 2006 is much higher than measured data. Therefore, in this study the author analyzes wave data at Hualain Harbor and typhoon data provided by Central Weather Bureau obtaining an empirical equation for typhoon swell period, i.e.

Tp=(0.041667×A+0.1321)×UR4s A=(DD3×R4)/(TR4Br)^4 Where Tp is the peak period in second ,DD3 is the distance between typhoon center and the station in nautical mile, R4 is the radius of maxium winds in nautical mile estimated by Rodolfo's method (2002), TR4Br、UR4s are the wave period at radius of maximum winds in second、sea-surface wind speed at radius of maxium winds in km.h-1 for stationary typhoon caculated by Bretschneider’s method (1976). The swell height empirical equaiton is:

Hs=0.2331×(HR4Br)×[√(R4/DD3)]×λ Where Hs is the significant wave in meter, HR4Br is the wave height at radius of maxium winds in feet for stationary typhoon calculated by Bretschneider’s method (1976).λ is the coefficient of wave height modification by Doppler effect(Liang,2003). Applying to typhoon Xangsane、Bilis、Korsa、Sinlaku,the typhoon swell hindcasting is acceptable.