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梅雨季伴隨豪雨之中尺度低壓個案研究

Case Study of the Mesolows Accompanied by Heavy Rainfall in the Taiwan Mei-Yu Season

摘要


本文選取1985年及1986年台灣梅雨期間,發生於台灣鄰近地區伴隨豪雨的3個中尺度低壓個案,利用每3小時地面與GMS衛星紅外線數據化資料以及每12小時探空觀測資料,進行個案診斷分析。除分析雲頂溫度與地面中尺度氣壓場、氣流場外,亦分析大氣環境的相當位溫與飽和相當位溫剖線。此外,並計算對流可用位能、對流理查遜數與可降水量。結果顯示,當台灣地區處於鋒後北來氣流控制下,中尺度低壓可因中央山脈的屏障作用而生成於西南部,而由海風與海上北來氣流交互作用提供氣旋式渦度,使中尺度低壓具有氣旋式環流,而成為中尺度氣旋。因海陸摩擦差異造成的氣旋式風切渦度,則有助於鋒上原有中尺度低壓移入台灣西北部時強度的維持。豪雨發生於中尺度低壓環流南側之個案與發生於低壓環流以內者,均顯示對流的增強與發展均與中尺度低壓有密切關係,中尺度低壓環流內近地層摩擦輻合,低壓南側西南氣流增強及其與局部環流(下坡風及陸風)產生的局部輻合,均有利於對流的增強與發展。最後,豪雨發生前後的環境場分析顯示,大氣原具有的大量不穩度可透過豪雨期間活躍的對流迅速釋放,唯不穩度的恢復在台灣西南部亦相當迅速。發生在西南部豪雨的環境,具有較大的對流可用位能、對流理查遜數與可降水量者,其對流活躍度、對流高度及降雨量亦大。

並列摘要


Three mesolow cases which accompanied by heavy rainfall and occurred over Taiwan and its adjacent area during 1985 and 1986 Taiwan Mei-Yu season were selected. Data used include surface observations and GMS infrared digital data at 3-h intervals and rawinsonde data at 12-h intervals. Mesoanalyses of the surface pressure and wind field and the cloud top temperature were carried out. Vertical profiles of equivalent potential temperature and saturation equivalent potential temperature were derived. Convective available potential energy, convective Richardson number, and precipitable water were computed.Results suggest that mesolow can be generated in southwestern Taiwan because the lack of cold air due to the blocking effect of the Central Mountain Range under the post-frontal prevailing northeasterly flow. The interaction of the sea breeze and the prevailing northeasterlies over the mesolow area provided the cyclonic vorticity in this case. The cyclonic wind shear due to the land-sea differential friction effect may help to maintain the mesolow intensity in northwestern Taiwan.The development and intensification of the convections were closely related to the mesolow for either the case which accompanied by heavy rainfall over the mesolow area or the case which had heavy rainfall that occurred to the south of the mesolow. The frictional convergence in the boundary layer over the mesolow area and the local convergence produced to the south of the mesolow by the interaction of the southwesterly flow and local circulations (downslope wind and land breeze) appeared to be responsible for the intensification and formation of the convections, and thus the heavy rainfall, over the same area.Finally, variations of the environmental conditions indicated that the large potential instability was released during the heavy rainfall period through the active deep convections. The recovery of the instability over south-western Taiwan was quite efficient under the prevailing low-level warm and moist southwesterly flows. For the two heavy rainfall cases over southwestern Taiwan, the one which had a greater convective available potential energy, a large convective Richardson number, and a greater precipitable water possessed more active convections, greater cloud top heights and greater rainfall amount.

被引用紀錄


姜禮鴻(2005)。花蓮地區梅雨季降水特性與豪(大)雨個案診斷分析〔碩士論文,國立臺灣大學〕。華藝線上圖書館。https://doi.org/10.6342%2fNTU.2005.02696
徐邦琪(2000)。台灣地區五-七月豪(大)雨之中長期預報與季內振盪〔碩士論文,國立臺灣師範大學〕。華藝線上圖書館。https://www.airitilibrary.com/Article/Detail?DocID=U0021-2603200719104762
梁育儒(2007)。2006年6月9日豪雨個案之模擬分析〔碩士論文,國立臺灣師範大學〕。華藝線上圖書館。https://www.airitilibrary.com/Article/Detail?DocID=U0021-2910200810553583

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