納莉颱風登陸後內核中低層環流結構變化特徵

The Mid-and Low Level Inner Core Circulation of Typhoon Nari (0116) after Landfall

周仲島(Ben Jong-Dao Jou) ； 高聿正(Yu-Cheng Kao) ； 李文兆(Wen-Chau Lee)

《大氣科學》 36卷3期 (2008/09) Pp. 163-178

摘要

本文利用中正和五分山都卜勒雷達合成風場，分析2001年納莉颱風登陸台灣後內核(inner core)中低層環流結構變化特徵。結果顯示，納莉颱風登陸初期內核環流結構仍是以軸對稱分量爲主，隨後軸對稱及非軸對稱分量隨著時間減弱，軸對稱分量減弱趨勢明顯大於非軸對稱分量，非軸對稱分量在環流結構中所佔比列逐漸增加。剛登陸時颱風的動能主要都集中在軸對稱分量，但隨著地形影響時間愈久，動能逐漸轉移到非軸對稱波數1~4的分量上。在徑向風部份，軸對稱及非軸對稱分量都是呈現減弱的趨勢，在大部份的時間當中，軸對稱分量較非軸對稱波數1、2分量小。此一結果顯示颱風登陸後，內核環流結構已不具典型渦旋結構（切向風遠大於徑向風）。納莉颱風登陸後中低層相對渦度和輻合最大值也由原本最大風速內側內縮至颱風中心，強度明顯減弱，顯示颱風中心填塞過程。由近中心30公里內平均渦度值估計其旋消時間尺度約180分鐘。本文並比較利用GBVTD反演之內核風場和雙都卜勒合成風場兩者差異，結果顯示GBVTD所反演之颱風主環流強度有高估的情況。

關鍵字

登陸颱風 ； 渦旋旋消時間尺度 ； 雙都卜勒合成風場 ； GBVTD

並列摘要

In this study, the mid- and low level inner core circulation of typhoon Nari (0116) after landfall is analyzed by using Dual-Doppler wind synthesis technique. RCWF and RCTP radial wind data are used for the synthesis.
The result showed, in the earlier period of landfall, the inner core circulation of Nari revealed pronounced axisymmetric structure. As time went by, both the axisymmetric and the asymmetric components (wave number 1-4) weakened. At the end of analysis time, the asymmetric component possessed a larger component than axisymmetric indicating a weakening storm. This result also suggested that the inner core circulation no longer possessed a typical vortex structure, i.e., the tangential wind was no longer stronger than the radial wind, after Nari made landfall.
The inner core maximum of mid- and low level relative vorticity and convergence also shrank from the inner side of radial maximum wind to the center indicating an eye filling process. In the study, the storm spin down e-folding time has been estimated (180 minutes) using vorticity averaged within 30 km of the center. In the study, the difference of circulation structure derived from GBVTD and dual-Doppler synthesis is compared and it shows that the GBVTD has a tendency to retrieve stronger mean tangential wind component.

並列關鍵字

Landfall typhoon ； Vortex spin-down time ； Dual-Doppler wind synthesis ； GBVTD