西北太平洋超級颱風快速增強現象之原因探討

Abstract

在熱帶氣旋的路徑預報已有長足進步的近20年間，強度預報精確度的進步仍然是十分地緩慢，因為強度變化是一個包含多重空間尺度的複雜問題，包含綜觀尺度、渦旋尺度、對流尺度、紊流尺度以及徵尺度，而在其中更加難以預報的現象就是快速增強(Rapid Intensification, RI)的現象。 在西北太平洋上近15年間，屬於超級颱風強度(強度達130kt以上)的颱風個案之中有百分之七十以上有發生快速增強的現象，只要當快速增強的現象發生在即將登陸前的時間點，在預警時間不足的狀況下將會對近岸地區造成十分大的損害。 本研究主要針對1994至2008年間西北太平洋上發生之70個超級颱風個案利用全球網格資料以及衛星觀測資料進行統計分析以及2009年兩個增強速率一快一慢的超級颱風個案利用海氣耦合模式進行高解析度數值模擬。在全球網格資料統計分析的結果顯示在颱風強度從category-1達到最大強度的過程中，綜觀環境場以及海洋場並沒有隨著不同的增強速度有明顯的關係；利用高解析度數值模擬的結果進行分析發現到內核區平均淨質量通量變化趨勢和強度變化趨勢配合地相當好，另外將內核區區分為對流區�層狀區可以發現到層狀區的動力結構對颱風強度有抑制作用而對流區的動力結構則是有助於颱風增強，而當層狀區佔內核區的比例減少後對流區佔的比例隨後增加使得低層垂直向上之淨質量通量增加，颱風強度就會有明顯的增強使得快速增加的產生。

While TC track forecasts have improved evidently in the past 20 years, progress in the accuracy of TC intensity forecasting is not obvious in contrast. Intensity change is a multi-scale interaction issue, including environmental, vortex, convective, turbulent and micro-scales. In such a complex problem, one of most difficult phenomenon to predict is rapid intensification (RI). In the past 15 years, there are over 70 percents of supertyphoons in western North Pacific underwent RI once during their life time. If the onset of RI was just before landfall, it would cause tremendous damage to the area TC passes trough in the shortage of precaution. This study will use the global analysis data and satellite observation to do the statistic for 70 supertyphoons during 1994-2008 period in western North Pacific and employ air-sea coupled model to proceed high-resolution simulations for two cases, one is RI case and the other is non-RI case. The result of statistic of observation does not show apparent relationship between RI index and environment during TC intensifying period. While analyzing the output of high-resolution simulations, it shows the trend of vertical net mass flux well matched the simulated intensity trend. Besides, using the method of partitioning TC into convective and stratiform components demonstrates the stratiform components play a role in inhibiting vortex intensification while convective components play a role in helping the strengthening of vortex. If the percentage of stratiform components decreases and the percentage of convective components increases, RI will happen.