MM5模式模擬之納莉颱風(2001)登陸時風場結構變化; Modeling the landing wind field structures of typhoon Nari(2001)

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題名:	MM5模式模擬之納莉颱風(2001)登陸時風場結構變化;Modeling the landing wind field structures of typhoon Nari(2001)
作者:	翁靜儀;Ching-yi Weng
貢獻者:	大氣物理研究所
關鍵詞:	徑向風;納莉;颱風;切向風;tangential wind;Nari;typhoon;radial wind
日期:	2008-12-23
上傳時間:	2009-09-22 09:43:37 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	台灣地形複雜，而當颱風登陸時會因地形作用而改變其結構，但對於颱風登陸期間之風場結構改變原因仍待進一步的探討。雷達資料可以用來分析颱風之三維結構，但是雷達對於低層大氣資料取得困難而受到很大的限制。本研究使用Yang et al.(2008)之PSU-NCAR MM5模擬納莉颱風(2001)的模式輸出，透過高時空解析度之模式資料，藉以分析納莉颱風風場在登陸臺灣期間之變化，更深入瞭解颱風與地形間的交互作用；並且由動量方程式來做診斷分析，了解颱風風場結構產生變化的原因。研究結果顯示，在海面上時颱風結構較為對稱，徑向風低層為入流、高層為出流。颱風接近陸地時，受到地形影響，徑向風低層入流增厚且中層出現一個傾斜向外的出流；切向風隨高度向外傾斜，颱風結構出現明顯不對稱性。颱風登陸期間，徑向風低層入流及中層出流皆持續增強變厚；切向風最大風半徑向外傾斜且半徑縮小，切向風最大值有減弱的現象。在眼牆之垂直速度上升運動區高度降低且最大值分布高度也降低，並向眼心收縮。MM5模擬結果與蔡(2006)用都卜勒雷達合成風場結構分析相當類似，故此MM5模擬應有相當的可信度。接下來更進一步使用每2分鐘之模式輸出資料對納莉颱風(2001)進行動量收支的分析，絕對角動量在遇到地形時，受垂直速度場的影響極大值向低層集中，絕對角動量變化主要受到氣壓梯度力及徑向水平平流項的影響；在切向風遇到地形時透過垂直傳輸將較小之切向風向上傳送，再加上摩擦效應使切向風減弱。經由計算徑向風動量收支項看出離心力項大於氣壓梯度力項，風場呈現超梯度風的情形，而低層徑向入流的增強來自於水平平流項，再配合垂直傳輸項將較強之徑向入流向上傳送，離心力項與氣壓梯度力項使得中層徑向出流增強。 After landfall, the typhoon structure is changed by the topography. The reason why the typhoon structure is changed by the topography is still unknown. Dual-Doppler radar synthesis can compose three-dimensional wind, but it is difficult to get the data of the lowest level. In order to understand the relationship between the typhoon and topography, this study utilizes the PSU-NCAR MM5 to investigate the structure of Typhoon Nari (2001) and mechanisms of the structures change during typhoon landing. Before landing, the typhoon wind field was symmetric. Low level radial wind was inflow and high level of radial wind was outflow. During landfall, the typhoon wind field was asymmetric. Low level inflow becomes thicker over land and the outflow appears near the mountain on the middle level. We have compared the model results with radar data, and found the tangential wind, radial wind and vertical velocity are well simulated by MM5. From analysis of the momentum budget equation, we found the downward absolute angular momentum (AAM) transport by the vertical advection. The tangential wind decreases at the low level through the upward transport of the smaller tangential wind. The results of the radial momentum budget showed that the tangential wind exhibited supergradient flow characteristics. The radial inflow was increased by the horizontal advection and the vertical advection. The increase of the radial outflow was caused by the centrifugal force and the pressure gradient force.
顯示於類別:	[大氣物理研究所 ] 博碩士論文

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