西北太平洋地區紮實颱風之天氣-動力特徵研究

A Study of Synoptic-Dynamical Characteristic of the Compact Typhoon in the Western North Pacific

陳嬿竹(Yen-Chu Chen)

指導教授 ： 李清勝

國立臺灣大學/理學院/大氣科學研究所/博士(2011年)

https://doi.org/10.6342/NTU.2011.01300

摘要

本研究重點在於探討西北太平洋地區紮實颱風之天氣與動力結構特徵。文中定義變數S以客觀代表颱風結構的紮實程度，較小的S值，表示該颱風結構較為紮實。研究過程中利用QuikSCAT衛星風場資料，針對1999 – 2009年219個颱風分析S之氣候特性；此外並利用WRF進行數值模擬，以探討紮實颱風結構之形成和維持機制。
分析結果顯示，在颱風發展初期，其風場特徵多屬於較為紮實之結構；意即結構紮實的颱風，有較高機會能持續增強。紅外線衛星雲圖的合成分析顯示，結構紮實個案的對流呈高度軸對稱特徵，且強對流集中在近中心處。為探討影響颱風結構之重要因子，本研究利用NCEP-GFS網格資料分析環境濕度與結構特徵之關係；結果顯示，在相對溼度較低的環境中，容易形成結構較紮實的颱風。
本研究利用WRF模式模擬結構紮實的玉兔颱風（Yutu，2007），並選取結構較不紮實的萬宜颱風（Manyi，2007）做為對比模擬個案。分析模式之徑向風場變化顯示，玉兔颱風之風速增強集中在近中心處，強渦度區（強慣性穩定度區）集中在颱風中心附近，其值亦明顯高於萬宜颱風。其次，本研究利用玉兔與萬宜之初始環境場，進行一系列之敏感度測試，包括植入不同強度和最大風速半徑的初始渦旋或考慮不同的初始相對濕度值。實驗結果顯示，初始渦旋在颱風結構變化上扮演重要角色，但在某些條件下（萬宜個案）環境條件亦會影響颱風結構的變化。改變相對濕度的測試顯示，相對較乾的環境有利於發展成結構較紮實的颱風，但若環境濕度太低，則將會抑制颱風的發展。

關鍵字

颱風結構 ； 紮實颱風 ； 數值模擬

並列摘要

This study focuses on the synoptic and dynamical characteristic of the compact typhoon in the western North Pacific. A structure parameter S is defined to provide a quantitative measure of the compactness of TCs. QuikSCAT oceanic winds are used to analyze the S parameters for 219 TCs during 1999-2009. In addition, compact typhoon is simulated using WRF to discuss the mechanism related to the development and maintenance of the compact typhoon.
The composite analyses show that the early intensification stage favors the occurrence of compact TCs, which also have a higher percentage of rapid intensification than do incompact TCs. Results from the composite infrared brightness temperature show that compact TCs have highly axisymmetric convective structures with strong convection concentrated in a small region near the center. Low-level synoptic patterns and environmental humidity are important environmental factors that determine the degree of compactness.
The WRF model is used to simulate the compact typhoon (Yutu, 2007) and the incompact typhoon (Manyi, 2007). Simulation results of Yutu show that the wind speed increases primarily at the inner-core region. The region of strong vorticity and high inertial stability is concentrated inside a small radius. Inertial stability for Manyi is much weaker. Results from the data analyses and numerical model simulation suggest that the compact cases are related mainly to the internal dynamics, whereas the incompact cases, the external forcing. The sensitivity experiments are designed to determine the roles of the initial vortex, external forcing and environmental humidity in the environment of Yutu and Manyi. Results of the sensitivity test are consistent with the finding from observational and control run simulation results.

並列關鍵字

Typhoon Structure ； Compact Typhoon ； Model Simulation

參考文獻

Bender M. A., and I. Ginis, 2000: Real-case simulations of hurricane-ocean interaction using a high-resolution coupled model: effects on hurricane intensity. Mon. Wea. Rev., 128, 917–946.

Black, M. L., and H. E. Willoughby, 1992: The concentric eyewall cycle of Hurricane Gilbert. Mon. Wea. Rev., 120, 947–957.

Brand, S., 1972: Very large and very small typhoons of the western North Pacific Ocean. J. Meteor. Soc. Japan, 50, 332-341.

Brennan, M. J., C. C. Hennon, and R. D. Knabb, 2009: The operational use of QuikSCAT ocean surface vector winds at the National Hurricane Center. Wea. Forecasting, 24, 621–645.

Boukabara, S.-A., R. N. Hoffman, C. Grassotti, and S. M. Leidner, 2002: Physically-based modeling of QSCAT SeaWinds passive microwave measurements for rain detection. J. Geophys. Res., 107, 4786, doi:10.1029/ 2001JD001243.