利用高解析度全球模式FV3GFS探討侵台颱風瑪莉亞(2018)受地形影響之路徑偏折;Track deflection of Typhoon Maria (2018) past Taiwan under Topographical Influences as Investigated by High-Resolution Global Model FV3GFS

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题名:	利用高解析度全球模式FV3GFS探討侵台颱風瑪莉亞(2018)受地形影響之路徑偏折;Track deflection of Typhoon Maria (2018) past Taiwan under Topographical Influences as Investigated by High-Resolution Global Model FV3GFS
作者:	阮子齊;Juan, Tzu-Chi
贡献者:	大氣科學學系
关键词:	FV3GFS;地形效應;角動量收支;渦度收支;FV3GFS;terrain effect;angular momentum budget;vorticity budget
日期:	2019-07-26
上传时间:	2019-09-03 12:20:06 (UTC+8)
出版者:	國立中央大學
摘要:	下一代全球預報模式FV3GFS的可縮放的網格提供了一個能增加解析度又兼顧運算效率的方法。本研究挑選了瑪莉亞颱風(2018)並使用可縮放網格提高至7公里進行模擬，發現此模式確實有能力模擬颱風並且優於各國機構預報，尤其是在路徑方面，移動速度與偏折幾乎完全掌握，降水部分也與觀測接近。基於FV3GFS提供了一個良好的模擬結果，本研究以此結果針對瑪莉亞颱風與台灣地形之關聯進行相關動力探討。將台灣地形效應移除後，發現在無台灣地形下颱風路徑並沒有偏折現象，中心風速變化部分也不明顯。因此可得出台灣地形對颱風造成的兩個主要影響，一為使其路徑往北偏折，二為使颱風中心風速增加。對此本研究以動量和角動量收支診斷來討論其風速的變化，發現在颱風逐漸靠近台灣時，瑪莉亞颱風於邊界層以下會產生更強的徑向入流並平流外圍較大的角動量至中心，使眼牆附近切向風速增加，但同時外圍約1度以外也會有較大的負徑向平流渦流產生，使風速減弱。路徑部分則以渦度收支診斷來討論其偏折，發現颱風路徑偏折為水平平流項主導，其餘各項加總為減速作用，將地形移除後則移動方向與移速都較為一致。與850百帕高度之水平風場做對應後，可知颱風在台灣西北側外海時，外圍環流受地形阻擋下產生的繞流，此繞流會造成駛流的改變使颱風路徑往北偏轉，中心風速增強也同樣為此繞流將外圍較大的角動量向內平流所致。 ;Global model FV3GFS, which has been chosen as the Next Generation Global Prediction System, provides a “grid stretching” technique which could not only increase resolution in the specific area but also keep its computational efficiency at the same time. In this study, we ap-plied this technique to simulate typhoon Maria (2018) with 7 km resolution. The results revealed that FV3GFS had capability of better typhoon track forecast. Compared to other agencies, translation speed and typhoon track deflection could be captured by the model well. Based on the previous results, we took advantages of FV3GFS to investigate the dynam-ical processes between Taiwan terrain and typhoon Maria. After removing terrain in Taiwan, we found that the northern deflection and the change of wind speed vanished. The results suggested that the terrain might lead to change in the path of typhoon and increase in wind speed around the radius of maximum wind (RMW). In this study, momentum and angular momentum (AM) tendency budget was preformed to verify the wind speed change, and we found that the strong inflow occurred below the planetary boundary layer, which transported the larger AM into the center and then enhanced the tangen-tial wind near eyewall. Meanwhile, outer part of the typhoon produced negative radial eddy advection, which slowed down the wind speed. Furthermore, vorticity tendency budget was performed to verify the track deflection. During the northern deflection of the typhoon track, we found that the northern deflection of the typhoon track was mainly caused by the horizontal ad-vection, and the sum of other terms decelerated the translation speed of the typhoon. Through these serial analyses, it turned out that the northern deflection of the typhoon track was primarily caused by terrain blocking, which produced a split flow to change the steering flow when ty-phoon was passing through the northwest of Taiwan ocean. The intensification near the eyewall was resulted from the larger AM advection, which was also caused by the split flow from outer part of the typhoon.
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