侵台颱風的最低中心氣壓與最大風速之極值統計

Abstract

本研究有二個目的，一是利用1949-1999年所有侵台颱風六小時最佳路徑點來研究颱風之空間分佈，另一目的為探討颱風的極值統計特性。至於空間分佈方面，接著將六小時最佳路徑點依照其氣壓大小及移動速度予以分類，分析各類颱風之空間分佈，發現颱風中心位置發生頻率最大的區域為 及 且隨颱風強度增加則愈偏東發生頻率越大。另外比較在花蓮港( ； )500Km以內不同距離各類型颱風每單位面積最佳路徑點次數，發現在靠近花蓮港300Km內以一、二級颱風為主，而完全沒有五級颱風，而在300Km~500Km間，除增加少部份之五級颱風，各級颱風均有減少趨勢，並且發現越靠近花蓮港，其移動速度越快，以時速25Km~30Km為主。 本文選擇五種極值分佈並利用力矩法、最大概似法與最小二乘法等三種推估參數方法，來探討1958年至2000年侵台颱風的最低中心氣壓與最大風速的最適極值函數及其極值統計特性。由結果發現，年計選用颱風最低中心氣壓資料的極值分佈以力矩法推估Weibull分佈的參數較適合，其推估50年颱風最低中心氣壓值為878.8mb。而颱風最大風速極值分佈以最大概法推估二參數的Weibull分佈參數為較適合，其推估50年重現期的推估值為180.2Knots。將颱風資料分奇數年及偶數年樣本對推估50年重現期的最低中心氣壓值或最大風速，與原樣本所推估結果相差較少；但依其來源將颱風資料分為早期的航照資料及後期的衛星影像資料二種樣本，則兩者所推估50年重現期的最低中心氣壓值或最大風速，與原樣本所推估結果相差較大。以全選取樣推估50年重現期的最低中心氣壓值或最大風速均會較以年計選用法推估結果高。

To know the spatial distribution and extreme statistics of typhoons passing around Taiwan is the aim of this paper. The data of 6-hour best track of typhoons that happened and passed around Taiwan during 1949 to 1999 were collected for the analysis of the spatial distribution of typhoons. Based on the central pressure and moving velocity, the typhoons were classified into five levels of strength and six kinds of moving velocity. From each group it is found that most typhoons happened in the region of and . Furthermore, stronger typhoons frequently occurred at far eastern region. In a region of 300 km centered at Hualien Harbor（ , ） happened much more than the other three groups and no typhoons of the fifth level passed in this region. The moving velocity of typhoons in the region are about 25~30 km/hr. The optimum extreme functions for minimum central pressure and maximum wind velocity of typhoons passing around Taiwan were examined in this paper. The parameters in five chosen functions were estimated by method of moment, maximum likelihood method and least square method, respectively, for the data of minimum central pressure and maximum wind velocity collected by central weather bureau for years from 1958 to 2000. That Weibull distribution estimated by method of moment is the optimum function for annual extreme data of minimum central pressure is found in this paper. The extreme value of minimum central pressure for 50-year return period estimated by the optimum function is 878.8 mb. The maximum likelihood method to estimate the parameters of Weibull function is the fittest distribution for the data of maximum wind velocity and its extreme valve for 50-year return period is 180.2 Knots. If the original data were divided into two groups by odd year or even year, their extreme values for 50-year return period were quite equivalent. However, when the original data before or after 1980 were separated by data source, these sets of samples had large difference between the estimated extreme values for 50-year return period. The extreme value of full series of minimum central pressure and maximum wind velocity of typhoons for 50-year return period is overestimated from that for annual series.