使用多部都卜勒/偏極化雷達分析凡那比颱風(2010)的眼牆重建過程

The Re-organizing process study of Typhoon Fanapi(2010) through multiple polarimatric/Doppler radar analyses

黃沛瑜(Pei-yu Huang)

指導教授 ： 陳台琦

國立中央大學/地球科學學院/大氣物理研究所/碩士(2012年)

摘要

2010 年9 月19 日，凡那比颱風於台灣東部海岸登陸，受中央山脈地形阻擋使颱風強度立即減弱。接下來的12 小時內，凡那比經歷了一重建過程(re-organizeing process)，並且在岡山雨量站帶來7 小時內下600 毫米的破記錄降雨。X 波段雙偏極化都卜勒雷達(Taiwan Experimental Atmospheric Mobil Radar, TEAM-R)於颱風期間設置於七股雷達附近進行同步觀測。使用Liou et al.(2012)提出的多雷達合成技術，使用七股、TEAM-R、墾丁和馬公等四顆雷達進行
三維風場的合成。
06UTC 至12UTC，一條強對流雨帶(長~200 ㎞)由筆直到彎曲的螺旋形狀，最終形成眼牆。同時，在七股雷達的徑向風場分布，明顯可見當颱風通過台灣西南部時，在山脈西側，風向從北風逐漸地轉變為南風，這個特徵在TEAM-R RHI 也同樣觀測到。另外，在颱風再增強(re-intensifying)期間，TEAM-R RHI 觀測到
的重要特徵是: 南風分量的增強是從低層往中高層延伸上去的。多雷達合成的三維風場重現了雨帶轉彎、渦旋的形成，到最後形成眼牆的過程。在此期間內，雨帶上有幾項重要的特徵: 水平風增強、強上升運動、正渦度的形成等。而在雨帶附近的弱回波區，則有反演出下沉運動。熱動力反演結果顯示: 在眼牆重建過程中，有壓力梯度的增強。溫度場則可見雨帶上的冷卻及渦旋中心的加熱。
TEAM-R 的雙偏極化參數搭配雨滴譜儀資料可以進一步地了解強雨帶上的微物理特性。雨滴譜儀觀測顯示，颱風期間的質量權重直徑(Dm)，約在0.5~2.5 mm，截距參數(Nw)約介在102.5~104 mm-1m-3。雷達反演DSD 的結果顯示，在06UTC 雨帶上的強上衝流造成了較大顆粒的雨滴；09UTC，上升運動稍減弱，產生了相對較小顆粒的雨滴；12UTC，眼牆上大範圍的上升運動，造成明顯較多的雨滴個數。
這是第一次在颱風重建階段，使用了四顆雷達觀測颱風結構的改變和與地形作用的影響。凡那比颱風重建過程中，切向風分量的肇始，中央山脈的阻擋可能扮演重要的角色。而螺旋雨帶上的強對流在爬坡過程中再進一步地被加強。到最後，颱風環流也會被加強並且重建。

關鍵字

以變分為基礎的多雷達風場合成

並列摘要

At 00 UTC, September 19, 2010 typhoon Fanapi made landfall on the east coast of Taiwan and its intensity was immediately weaken due to high Central Mountain Ridge. In the next 12 hours, Fanapi went through a reorganizing process and brought record breaking 600mm rainfall within 7 hours to Gunsan station in southwest Taiwan. A mobile X-band dual polarization/Doppler radar, TEAM-R (Taiwan Experimental Atmospheric Mobil Radar) had been deployed near the Chigu S-band Doppler radar, together with Kenting S-band radar, and Magong C-pol radar these four radars provided great opportunity to study this event. A new
multi-Doppler radars wind field retrieval method proposed by Liou and Chang(2009) was used to synthesize three dimensional wind field.
From 06 UTC to 12 UTC , a strong convective rain band was slowly gaining its curvature and evolving into a spiral shape. At 12 UTC, an asymmetric eye wall was observed. During the same period, from Chigu S-band single Doppler wind pattern, it is obvious that wind direction changed from north wind to gradually increasing south wind at Chigu as the typhoon center passed southwest of Taiwan Island. At
09UTC, a vortex circulation was found at the lee side of Central Mountain Ridge in the synthesis wind field. The retrieved vortex-like pattern was near the lowest pressure location of surface stations observation. During the re-intensifying period, the other important feature is observed by TEAM-R RHI (range-height indicator) mode, the south wind component intensified from low level to mid and high level in a few hours.. The dual- polarimetric parameters of TEAM-R are used to study the microphysical characteristics of this torrential rain band. Three nearby disdrometers and TEAM-R radar further provide rain drop size distribution (DSD).The preliminary results showed the rather large mass weighted diameter Dm(~2.2 mm) and high concentration Nw (~104 mm-1m3) during the heaviest rain period.
For the first time in Taiwan, four radar systems had chance to observe the structure change and study the influence of the topography during the reorganizing stage. The blocking of the Central Mountain Ridge may play an important role of
the initiation of the tangential wind component. The stronger convection of the spiral band was further enhanced by the up-slope forcing. Subsequently, the typhoon circulation was also strengthen and re-organized.

並列關鍵字

variational-based multiple-Doppler radar synthes

參考文獻

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