Gaoyuan qixiang (Feb 2024)
Analysis of the Dynamical Structure and Genesis of Two Different Life-History Eastward Moving Plateau
Abstract
The NCEP reanalysis data were utilized to diagnose the structural characteristics and evolutionary mechanisms of two plateau vortex processes that moved eastward out of the plateau on June 25-27， 2008 and June 4-10， 2013.The data were also used to explore the structural characteristics of the two long and short track plateau vortex processes and the influencing factors that caused their different life histories.The results show that： （1） During the Zhaduo vortex activity with a short path， the South Asian high pressure is flattened， the upper-level jet stream is southward and the plateau vortex moves out of the plateau in the slump trough.During the Qumalai vortex activity with a long path， the South Asian high pressure has a north arch， the plateau vortex is in the northwest airflow under the South Asian high-pressure ridge， the subtropical high is southward and the plateau vortex is strengthened with the eastward movement of the trough， accompanied by the eastward movement of the southwest vortex.（2） The two plateau vortex processes exhibit distinct structural characteristics， especially when the Zhaduo vortex is strengthened on the plateau and when the Qumalai vortex is strengthened again after coupling with the southwest vortex.The former vortex is in the deeper positive vorticity and upward motion layer at 600~350 hPa and also has the structural characteristics of strong divergence in the upper troposphere.The latter has the structural characteristics of high， middle， and low positive vorticity penetration in the troposphere， ascending movement in the troposphere， and weak divergence in the troposphere.（3） The diagnosis of total vorticity budget shows that the change of divergence term plays a decisive role in the change of total vorticity variability of low vortices.The strength change of Zhaduo vortex is consistent with the divergence term change.The influence of vertical transport term and horizontal advection term are strengthened during the accompaniment of Qumalai vortex with the southwest vortex.（4） Regarding the budget analysis of the 500 hPa positive vorticity variability in the central region of the vortex， the results show that when there is no activity of the southwest vortex， the plateau vortex contributes mainly to the 500 hPa positive vorticity variability of the plateau vortex due to convergence.When there is activity of the southwest vortex， the vertical transport of positive vorticity becomes more important with the superposition and companionship with the southwest vortex in the vertical direction.
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