梅雨季伴隨華南西南風爆發之低壓發展

A Study of Cyclone Development Associated with Southwesterly Surges in Southern China during Meiyu Season

侯喜真(Shi-Chen Hou) ； 陳泰然(Goeorge Tai-Jen Chen)

《大氣科學》 29卷3期 (2001/09) Pp. 203-228

摘要

本文選取1987-1993年春末夏初5、6月期間造成華中與華南地區西南風爆發的31個低壓擾動個案，以探討此種低壓之結構與演變過程，這些低壓可分為移動性和滯留性兩類，其伴隨之綜觀形勢有相當明顯的差異。移動性低壓擾動均快速東移，且均伴隨中高對流層短波槽；滯留性低壓擾動在低對流層均屬雙低壓中心之結構，而中高對流層則在東亞大陸與西太平洋出現一準阻塞長波脊，此類低壓所造成低層西南風的增強較移動性低壓擾動所造成者更為持久且範圍更大。
就低壓發展的動力觀點而言，低壓系統發展成熟期之垂直結構特徵，可明顯分為四類，即中低對流層擾動型、垂直偶合型、垂直重疊型以及對流層頂折疊型等四類。利用位渦保守性與可反演性，以位渦反演的結果探討各類低壓擾動發展的機制與垂直結構的演變。結果顯示，不同類型的低壓擾動分別具有不同的位渦垂直結構與演變過程，而除了對流層頂折疊型以外，在其他三類型低壓的發展過程中，水氣凝結之潛熱釋放皆扮演一定程度的角色，而高層系統則可藉由垂直偶合、垂直重疊以及對流層頂折疊等三種不同的方式，導致低層低壓擾動的發展。

關鍵字

西南風爆發 ； 低壓擾動 ； 位渦 ； 潛熱釋放 ； 垂真偶合 ； 垂真重疊 ； 對流層頂折疊

並列摘要

During Meiyu season of May-June 1987-1993, there were thirty-one cases of cyclone development to the leeside of the Tibetan Plateau that caused the southwesterly surges over southern China. These cyclones can be categorized as moving and stationary types. For the moving type, the cyclone center usually moved eastward fast under the influence of the upper level short-wave trough. For the stationary type, cyclone usually possessed two centers in the lower troposphere, with a quasi-stationary blocking situation occupied the upper level over East Asia and the Western Pacific. In general, the southwesterlies caused by the development of stationary-type cyclone last longer and covered larger area as compared to that for the moving type.
Based on the vertical structure of potential vorticity at the mature stage, these cyclones were classified into four types: lower-troposphere, vertical-coupling, vertical-superposition, and tropopause-folding types. Using the property of invertibility of potential vorticity, the development and the evolution of vertical structure of different types of cyclones were investigated. Results showed that different types of cyclones existed different vertical structure and different evolution characteristics of potential vorticity. Latent heat release usually played an important role for the development of cyclones except for the tropopause-folding type. In addition, the upper level system could impact the development of cyclone through vertical coupling, vertical superposition, and tropopause folding processes.

並列關鍵字

Southwesterly surges ； Cyclone development ； Potential vorticity ； Latent heat release ； Vertical coupling ； Vertical superposition ； Tropopause folding