MECHANISM STUDY FOR ANOMALOUS VARIATION OF THE WESTERN PACIFIC SUBTROPICAL HIGH DURING THE REBUILDING PROCESS OF THE MEIYU OVER THE YANGTZE RIVER VALLEY IN 1998
SU Tong-hua
LV Si-si
YUAN Zhuo-jian
Abstract：Based on the NCEP Reanalysis 2 data,the variation of geopotential heights during the rebuilding process of the Meiyu over the Yangtze River valley in July 1998 is analyzed by using the linear geopotential equation.It is revealed that the rebuilding of the Meiyu is due to the southward retreat and enhancement of the western Pacific subtropical high (WPSH),which is mainly characterized by respective decrease and increase of geopotential heights in the northern and southem part of the WPSH.This process consists of two stages,i.e.,the first stage of decreasing and southwardretreating,and the second stage of increasing and maintaining.Moreover,the weather systems in high and low latitudes play a collective role in the adjustment process.The vorticity-related geostrophic mode and the friction divergence are the two most important items.Specifically,without considering the boundary effect,the former's contribution order is 101 gpm and the latter's is 100 gpm,yet with the contribution constrained to the lower level of the troposphere.Due to deep depression troughs induced by Rossby waves in the middle and high latitudes,the geopotential height to the north of WPSH tends to decrease persistently under the impact of a vorticity-related geostrophic mode.Similarly,it is also this item that makes geopotential heights to the south turn to increase after reaching a minimum because of the northward movement of an equatorial anticyclone.Through positive feedback,the friction divergence item tends to accelerate the aforementioned decrease and increase trends.
Keywords：linear geopotential equationrebuilding of the Meiyuwestern Pacific subtropical highdouble ridgelines
Publication Date：2017-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：10( 588-597 )