Impact Of Upper Trough On Rapid Intensification And Remote Heavy Precipitation Of Typhoon

First of all,using the atmospheric reanalysis data provided by ECMWF?European Centre for Medium-Range Weather Forecasts?and the best track data provided by IBTr ACS?International Best Track Archive for Climate Stewardship?to carry out statistical,composite and diagnostic analysis on the typhoon of rapid intensification?RI?process with different outflow types.There are 65?21?times of northerly?easterly?outflow pattern,which is mainly at lower?higher?latitude and dominated by the northwest?northeast?track.The interaction height between upper trough and typhoon is mainly 150-300 h Pa.It is favorable condition for the development of typhoon when the distance between the southwesterly jet in front of trough and typhoon is about 5-10°and the vertical wind shear around the typhoon is still weak.As the southwesterly jet in front of the trough approaches the typhoon,the upper divergence caused by the southwesterly jet strengthens the divergence and expands outflow channel of typhoon as well as the secondary circulation below the southwesterly jet entrance area enhances the convection development in typhoon troposphere especially in the lower layer.All of them promote the rapid intensification of typhoon.The typhoons which RI process with Sp?single channel towards the polar?upper outflow occurred in the South China Sea are analyzed.When the distance between the southwesterly jet entrance area in front of the upper trough and typhoon is within 10°,the cold advection behind the trough does not affect the development of the typhoon and the vertical wind shear of 850-200 hpa is below 10 m·s^-1,the southwesterly jet in front of the trough can drive the outflow of the typhoon towards to the north,strengthen the outflow channel of typhoon and promote the development of the upper divergence of typhoon,which inducing the rapid intensification of typhoon.At 12h before RI,there are obviously interaction between upper trough and DOT?9318?.Especially at 6h bofore RI,the sudden eruption of typhoon upper divergence and the REFC?eddy flux convergence of relative angular momentum?are significant early warning on the rapid development of DOT?9318?.After the beginning of RI,the interaction between the upper trough and WUTIP?1321?is enhanced as the distance between the two decreases gradually.Because the distance between the upper trough and SON-TINH?1223?is more than 40°,the southwesterly jet in front of the upper trough can not affect the development of the typhoon upper divergence.Therefore,the trough has no obvious influence on the RI process of SON-TINH?1223?.Finally,using the 0.25°×0.25°FNL?Final Operational Global Analysis?data provided by NCEP?National Centers for Environmental Prediction?and the high-resolution three-source merged precipitation data provided by National Meteorological Information Center,the interaction between the mid-latitude upper trough and Lekima?1909?on remote heavy precipitation is investigated involved dynamic and thermal processes.The northwest of typhoon is gradually located in the ascending area of the southwesterly jet in front of the trough as the weak positive Potential Vorticity?PV?anomaly is advected horizontally from the mid-latitude upper trough to typhoon.The deep troposphere warm advection is located in the area of 3-5°to the northwest of typhoon,which enhances the ascending motion at the northwest of typhoon.The approach of dry and cold air behind the upper trough promotes the middle-latitude baroclinic frontogenesis at the northwest of typhoon,which further enhances the dynamic uplift of the typhoon at remote heavy precipitation area.