The Causation Analysis of Abnormal Tracks Sustained Departure Tibetan Plateau Vortex Accompanying the Northward Moving Tropical Low

By using the NCEP/NCAR reanalysis data, historical weather graphs, The Plateau vortex and shear line yearbooks and historical tropical low data, on basis of ambient field analysis of abnormal track of sustained departure Tibetan Plateau Vortex ( SDPV ) accompanying the northward moving tropical low before, 3 spinning over Hetao region examples of SDPVs accompanying with the northward moving tropical low from 1998-2012 with different phases of wind fields characters and vorticity budget at middle troposphere levels are analyzed.Results show that the northward moving typhoon or tropical low between east of China main land and west 140 ºE will make the SDPVs moving in a relative weak shear flow field and blocking and moving east slowly over the Hetao region. The tropical low activities can influence the SDPVs ambient wind field, which will change its own wind field structure. In the whole spinning process of the SDPVs over Hetao region, the vortex usually moves along the maximum wind direction in that region, which means the dissymmetrical wind structure influences a lot to the track of spinning SDPVs over Hetao region. In the spinning process over Hetao region, the vortex moves to the region of positive vorticity strengthening region, there are positive voritcity ratio in vortex area on 500hPa, positive voritcity ratio region distribution consistent with the big wind field region. The vortex usually moves to the region of positive vorticity region ratio centre of the vortex region. The average positive vorticity region ratio changes will influence the spinning track of the vortices. All above means that sustained Plateau vortex in a weak shear wind flow field, the maximum wind and positive vorticity ratio are the most important dynamical factors to influence the vortex track and spinning process over the Hetao region. The causation analysis of SDPVs spinning over the Hetao region can afford the basis to predict the abnormal tracks of the vortices, which usually lead to storm rain and flood in that region.

Key words: Tibetan Plateau Vortex, tropical low, abnormal Tracks, causation analysis