海棠颱風登陸台灣前內核結構演變之研究

A Numerical Study of the Inner Core Structure Change of Supertyphoon Haitang (2005) Prior to Its Landfall in Taiwan

簡國基(Guo-Ji Jain)

《大氣科學》 39卷1期 (2011/03) Pp. 83-93

摘要

海棠颱風(2005)登陸台灣前，除了出現逆時針打轉的路徑外，颱風內核結構同時也有明顯的變化；都卜勒雷達觀測資料顯示，當颱風中心靠近台灣時，眼牆南側象限有線狀對流加強現象，該線狀對流逐漸旋繞併入眼牆，接著即出現颱風內核區之對流增強。本研究使用WRF-ARW中尺度模式進行高解析度（水平4公里）數值模擬的結果發現，台灣地形阻擋使繞山氣流與颱風內核環流產生低對流層之動力輻合，激發內核南側線狀強對流；隨後，該線狀強對流被併入眼牆區，促使眼牆東側位渦值及對流強度皆明顯增強，颱風眼結構也逐漸調整成橢圓狀。位渦擾動量收支分析結果顯示，非對稱加熱作用下之位渦通量項以及颱風平均風場作用下之位渦擾動通量項是導致眼牆東側位渦加強的主要貢獻項；線狀強對流併入眼牆時，颱風強度會短暫增強，此增強的過程在趨勢上是呈現振盪且強度漸漸加強之型態，同時內核不對稱強風速區將轉而出現在眼牆東側象限，本模擬結果亦顯示，線狀強對流完全併入眼牆東側（發生於積分時間30~31小時）約2~3小時後，颱風內核中心逐漸開始轉向北移行，此運動北轉為海棠颱風內核完成逆時針打轉路徑的關鍵過程，本實驗未來將進一步研究眼牆東側強位渦發展與該北轉運動是否有顯著關聯並探討其中的動力機制。

關鍵字

颱風內核 ； 眼牆不對稱對流 ； WRF-ARW模式

並列摘要

The inner structure of Supertyphoon Haitang (2005) took place temporal changes during the looping motion before its landfall in Taiwan. The Doppler observations show that an enhanced rainband is induced along the southern quadrant of the eyewall, which is then merged into the east sector of the eyewall. Two numerical simulations are conducted using the advanced WRF model with a 4-km fine mesh to examine the physical processes responsible for the above eyewall evolution. It is found that the initiation of the enhanced rainband is attributed to the low-level convergence between the around orographic flow and the inner-core circulation. The results of potential vorticity(pv) budget indicate that the pv fluxes due to asymmetric of diabatic heating play the major role on strengthening the eyewall pv and the winds over the eastern quadrant, which leads to a southerly asymmetric advection flow to complete the looping path.

並列關鍵字

Inner core ； Asymmetric eyewall convection ； WRF-ARW