康芮颱風(2013)結構演變與對流降水關係之研究

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2016

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2013年8月下旬輕度颱風康芮(Kong-Rey)侵臺期間,衛星及雷達觀測資料均顯示其雨帶結構明顯不對稱,強對流雨帶多位於颱風中心之南側與西南側,且其渦旋垂直結構亦有傾斜現象,導致最大降雨區位於離颱風中心較遠之中、南部地區,累積雨量達500-700 mm以上,造成不少災損與人員傷亡,反觀離颱風中心最近之臺灣北部及東半部地區雨量則明顯偏少,多數地區累積雨量甚至不到50 mm。 本研究利用雲解析風暴(CReSS)模式模擬康芮颱風侵臺時之結構與降水演變,並進行地形敏感度實驗及位渦傾向診斷。模擬結果顯示,康芮颱風位於海面上時,其雨帶之不對稱性(南強北弱)主要為環境流場東北向西南之垂直風切造成,而雨帶成因為颱風環流西側之偏北風與巴士海峽之西南風輻合所致,且隨著康芮颱風北上接近臺灣地區,此輻合區與雨帶亦隨之北移進入臺灣陸地,配合地形強迫舉升,產生南北走向平行山脈之滯留性雨帶,遂於臺灣中、南部地區造成致災性豪雨。 地形敏感度實驗中,Control Run實驗因地形鎖定降水區域,使臺灣陸地上空產生大量潛熱釋放與垂直運動,導致中層正位渦隨時間增加,康芮颱風中層渦旋因而產生偏西分量移入臺灣陸地,而其低層之颱風中心則受地形阻擋持續北移,兩者遂產生明顯之相位差,使渦旋垂直結構隨高度向上向臺灣地形傾斜。No-Terrain Run實驗中,移除臺灣之高山地形,颱風北移時潮濕西南風仍可匯入康芮颱風之中心附近,維持中心附近螺旋雨帶之生成與發展,進而使接近颱風中心之臺灣北部與東半部地區累積雨量較Control Run明顯增多,但因缺少地形鎖定之滯留性雨帶,臺灣上空中層之正位渦值明顯較Control Run小,使康芮颱風之中層渦旋無法產生明顯之偏西分量,遂可維持較垂直之渦旋結構。
Tropical Storm (TS) Kong-Rey (2013) affected Taiwan in late August 2013. During this period, satellite and radar observations indicated clear asymmetric structure, with its active convection and rainfall located most to the south and southwest of the typhoon center and a tilted vortex vertical structure. As a result, the maximum rainfall in Taiwan was over its southwestern region and far from the typhoon center, with an accumulative amount of over 500-700 mm that caused much damage and several casualties. On the other hand, over northern and eastern Taiwan closer to the storm center, only little rainfall was received (mostly below 50 mm). In this study, the Cloud-Resolving Storm Simulator (CReSS) is used to successfully reproduce the evolution of TS Kong-Rey and related whether phenomena during the period when it affected Taiwan. The control (CTRL) simulation shows that the asymmetric rainfall of the storm was mainly due to the strong vertical wind shear (from northeast to southwest) in the environmental flow during the approach of Kong-Rey over the Bashi Channel. An intense rainband formed along the convergence zone between the northerly typhoon circulation and the southwesterly flow over the southern Taiwan Strait. Later when the storm moved further north, this rainband also moved overland into southwestern Taiwan and became stationary and north-south oriented (parallel to topography), and produced heavy rainfall and the subsequent hazards with enhancement from terrain uplifting. In the CTRL experiment, the convection is also phase-locked to the topography of Taiwan, and the associated latent heating effect leads to an increase in mid-level potential vorticity (PV) with time and a westward moving tendency of the mid-level vortex. In contrast, the low-level storm center, being blocked by the Central Mountain Range (CMR), continues to move northward as observed and results in the significant vertical tilt (toward the Taiwan terrain with height). In the “no-terrain” (NT) where the Taiwan topography is removed, the strong convection and rainband become migratory and move with the storm, more rain is simulated over northern and eastern Taiwan, the PV production over Taiwan is less, and the vertical tilt of the storm is also reduced compared to the CTRL. Thus, the topographic effect of Taiwan on convection and precipitation was also a key factor (in addition to the vertical wind shear) in the maintenance of the tilted vertical structure of Kong-Rey (2013) when it passed by Taiwan.

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康芮颱風, 渦旋垂直結構, 位渦, 地形效應, 臺灣, Typhoon Kong-Rey, vortex vertical structural, potential vorticity, topographic effect, Taiwan

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