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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/4914


    Title: 華南春季冷鋒之個案研究;Case Study of a Springtime Cold Front in South China
    Authors: 高長霖;Chang-lin Kao
    Contributors: 大氣物理研究所
    Keywords: 對稱不穩定;鋒生函數;地形作用;濕位渦;conditional symmetric instability;moist potential vorticity
    Date: 2008-07-05
    Issue Date: 2009-09-22 09:41:09 (UTC+8)
    Publisher: 國立中央大學圖書館
    Abstract: 本文選取一個春季在華北地區生成之後南移到華南地區的冷鋒系統,採用中尺度模式(MM5)進行模擬,以探討此春季冷鋒經過華南山區時的鋒面結構演變過程。 當鋒面南移到華南山區時,鋒面移動速度減緩的同時,鋒面低層會受到地形的阻擋作用而變形。在鋒面過山階段,地面鋒附近的水平輻合作用,造成低層鋒生並且引起鋒面前緣低層的強烈上升運動;此外,還有華南山區的地形重力波,以及冷鋒面的重力流特徵,這三者的作用疊加在一起,使得鋒面帶上的垂直運動場呈現上升、下降的間隔式分布。經過鋒生方程中的扭轉項作用,又使得沿著鋒面上也呈現鋒生、鋒消的間隔式分布型態。 當鋒面過山時,雖然因地形影響改變了垂直運動場,造成鋒面爬山階段的鋒消,但是鋒面前的暖濕空氣卻會因鋒面的舉升作用而達到飽和,此種飽和的大氣環境,正符合條件性對稱不穩定(CSI)理論的基本假設。 透過濕位渦(MPV)的分析,可以瞭解在鋒面系統中處於飽和而且MPV<0的區域,若再配合地形與鋒面次環流的舉升運動,這些區域可能就會有CSI的發展。本個案適合CSI發展的區域主要分布在鋒面帶中的暖側,並且呈帶狀分布。這些區域的形成都是因為鋒面帶上的鋒生作用造成,而地形造成的垂直運動場疊加在鋒生次環流上,又是使鋒面帶呈現鋒生、鋒消間隔式分布型態的主要原因,因此,地形作用對於鋒面帶上可能產生CSI的位置就扮演重要的角色。 The PSU/NCAR mesoscale model (MM5) was used to investigate the topographical effect on the structure of a springtime cold front passing East China. The observational analysis shows that the surface frontal system will be retarded and deformed by the topography, when the cold front moves southward to the Wu-I Mountain Range. Owing to the surface convergence effect, the cold front experiences a low level frontogenesis process when it climbs up the mountains, and hence induces a strong upward motion. Furthermore, both the mountain gravity wave and the gravity current of cold front, can enhance or weaken the upward motion. These three effects enhence the up/down interlaced pattern of the vertical motion and induces the frontogenesis/frontolysis process along the front through the tilting effect. The lifting of the cold front by the mountains favors the moisture in the warm sector to reach saturation. This condition is consistent with the conditional symmetric instability (CSI) theory. Through the analysis of the moist potential vorticity (MPV) , saturation condition and vertical motion, the result shows that the suitable regions for CSI to develop are distributed over the warm side of front band. So, the topographical effect plays an important role in the formation and distribution of CSI in a frontal band.
    Appears in Collections:[大氣物理研究所 ] 博碩士論文

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