Impact Of Tropopause Folds On Deep Convection Over The Tibetan Plateau

In this paper,the effect of upper-level forcing on plateau convection was studied based on the ERA-Interim reanalysis data,confluent precipitation data of automatic station in China and Cmorph,Trmm satellite data and hourly TBB data from FY-2E,using statistical-weather Diagnostic analysis,mesoscale numerical simulation,piecewise vorticity inversion and Synthetic analysis.The results showed that:1)The climatological characteristics of plateau deep convection and tropopause folds with different intensities are statistically analyzed and the spatial-temporal distribution of the plateau convection-folding is summarized,found that the folding mode is located on the northwest side of the plateau with deep convection.2)Through statistical analysis of folding classification,it is found that the occurrence of shallow folds is more frequent but the plateau convection related to middle folds is more intense.3)The mechanism of the influence of folds on convection is analyzed,and a model of the effect of folds on convection on the plateau is summarized bashed on statistical analysis.The statistical synthesis analysis of environment fields related to folding found that folds affects vertical and horizontal circulation.The sinking motion corresponding to folds and the ascending motion of plateau convection meet at the low-middle level and forming a counterclockwise vertical circulation.The mass and momentum transport of the sinking branch cause mass accumulation to force vertical uplift near the convection area,which is conducive to the development of plateau convection.At the same time,the fold descending also changes the circulation of the lower atmosphere.As a effective barrier from upper-level,it blocks the northwestern warm and humid air flow from climbing to the north,accumulates and rises near the target area(plateau convection area),and provides sufficient water vapor.meanwhile,the cold and dry air accompanying the folding increases the instability near the convection area.The downward transmission of isentropic PV at high-level causes the vorticity in the lower layer to increase,which in turn Intensify convective development.4)Through typical case study and numerical simulation,a more detailed physical image of coordinated devolopment of high-level folds and plateau convection is further depicted.The synergy of the high-low systems led to the occurrence and development of the deep convection event on the plateau.The development and growth of convection is the result of downward vorticity of the upper layer,the upward vorticity of the lower layer,and the connection between the two.The upper vorticity downward transmission is caused isentropic potential vortex advection,and the upward extension of the lower vorticity is mainly the result of the release of latent heat of condensation Through piecewise vorticity inversion.The above studies can not only reveal the climatological characteristics of deep convection in the plateau,but also deeply understand the matching relationship and action mechanism between the Tropopause Folds and deep convection.This is important in both extreme weather and climate change.