DEFORMATION OF MOISTURE FLUX CIRCULATION SURROUNDING THE LANDFALL TYPHOON BILIS

The deformation parameter (DP), which is defined as the product of shear deformation and stretching deformation of moisture flux circulation, is introduced. The tendency equation of DP is derived in pressure coordinates. Furthermore, DP is used to diagnose the deformation character of moisture flux circulation in the periphery of Bilis. The analysis showed that before Bilis landed, DP presented eight abnormal areas, which distributed alternately and closely encircled the low-pressure center. This indicated that the moisture flux circulation in the periphery of Bilis rotated counterclockwise and stretched longitudinally and latitudinally to deform. After Bilis landed, DP weakened gradually and its regular pattern of horizontal distribution loosened. The shear and stretching deformations of moisture flux circulation surrounding Bilis weakened after the typhoon landed. The deformation of moisture flux circulation in the periphery of Bilis mainly appeared in the middle-lower troposphere. There existed 1/2 phase difference between the shear and stretching deformations in the vertical-latitudinal cross section and a π/4 phase difference between them on the horizontal plane. As Bilis landed and further moved inland of China, the intensities of DP, shear and stretching deformations decreased, meanwhile their vertical and horizontal structures became irregular. The chief dynamic factors responsible for the deformation of moisture flux circulation in the periphery of Bilis were the three terms associated with the three-dimensional advection transportation of DP, square difference between shear and stretching deformations coupling with Coriolis parameter, and horizontal gradient of geopotential height before Bilis landed. The last two dynamic factors impacted jointly on the deformation of moisture flux circulation after Bilis landed.

作 者： RAN Ling-kun YANG Wen-xia HONG Yan-chao   作者單位： RAN Ling-kun,HONG Yan-chao(Institute of Atmospheric Physics,Chinese Academy of Sciences,Beijing 100029 China)

YANG Wen-xia(Institute of Atmospheric Physics,Chinese Academy of Sciences,Beijing 100029 China;Graduate School of Chinese Academy of Sciences,Beijing 100049 China) 

刊 名： 熱帶氣象學報（英文版）  英文刊名： JOURNAL OF TROPICAL METEOROLOGY  年，卷(期)： 2009 15(2)  分類號： P457.6  關鍵詞： deformation parameter   shear deformation   stretching deformation   moisture flux circulation