Analysis Of The Characteristics Of Precipitation In The Inner Core And Outer Spiral Rain Belt Of Typhoons That Landed In East China

In this paper,NCEP reanalysis data,ECMWF reanalysis data,typhoon precipitation separation data and other data were used to conduct statistical analysis on the characteristics of typhoon precipitation,the precipitation of the typhoon core and its peripheral spiral rain belt that made landfall in east China from 2000 to 2018,and the causes of heavy precipitation caused by the typhoon core and peripheral spiral rain belt were preliminarily discussed.In this paper,the mesoscale characteristics and the genesis of heavy rainfall in the helical rain belt of its core and periphery are analyzed.The main conclusions are as follows:(1)Typhoons affecting eastern China mainly make landfall in summer.Both the frequency of typhoons landing and the frequency of typhoons bringing extreme precipitation reflect the characteristics of "unimodal" monthly distribution,which is mainly concentrated in July-September and reaches its peak in August.The precipitation of typhoons landing in east China is mainly distributed in the southeast coastal areas,and has the characteristics of gradually decreasing from the coast to the inland,from the south to the north.The precipitation was mainly concentrated in Fujian and Zhejiang provinces,the Yangtze river delta,northern Jiangxi province,central and western Anhui province and Jiao Dong peninsula.The precipitation fall area of typhoons landing in east China is mainly related to the typhoon path,the topography of east China,the typhoon intensity and the atmospheric environment field,etc.Good dynamic,thermal and water vapor conditions will also cause typhoons to produce heavy precipitation.(2)With the landing of the typhoon,the precipitation in the outer spiral rain belt is strengthened,and the precipitation in the core is weakened and asymmetrical.In the spiral rain belt around the typhoon in Fujian,the precipitation is mainly from northeast to southwest and east to west.At the tail of the outer spiral rain belt,new convective cells are constantly generated,which move tangentially along the typhoon circulation and merge into the rain belt,showing obvious "Train Effect".Mesoscale convection is more common in the spiral rain belt around the typhoon than in the typhoon core.The movement path and topography of the typhoon will affect the generation of the mesoscale convection system.In typhoon circulation,mesoscale heavy precipitation usually occurs in the cold cloud region where the black body light temperature(TBB)?-52?,and the heavy precipitation center occurs in the TBB gradient region.(3)Core precipitation is distributed in the landfall process of typhoon on the left side of the path(hereinafter referred to as L-type typhoon).The lower layer on the left side of the path maintains airflow convergence,and the upper layer maintains airflow divergence.The environmental horizontal wind shear points to the southwest,which is conducive to the generation of heavy precipitation on the left side of the typhoon core.On the right side of the precipitation distribution path of the kernel(hereinafter referred to as R-type typhoon),the low-level airflow converges and rises,and the upper level diverges on the right side of the path.The vertical wind shear in the northeast direction is conducive to the precipitation of the r-type kernel.L-type typhoons are mainly controlled by warm advection.Cold advection develops and maintains on the left side of the path.The intersection of cold and warm advection provides more unstable energy for the formation of precipitation.During the landfall of R-type kernal precipitation typhoon,the northeast quadrant of the typhoon circulation maintains warm advection,which is conducive to the warming of the lower layer and the reduction of atmospheric stability.The water vapor transported by the southward jet of the lower layer in the southeast extends to the north of the typhoon,which is conducive to the occurrence of the kernel precipitation on the right side of the typhoon path.The development and merging of mesoscale clouds is an important reason for the occurrence of heavy precipitation in the outer spiral rain belt.The interaction of abundant water vapor and convergence and divergence fields in high and low altitude is conducive to the occurrence of heavy precipitation in the outer spiral rain belt.The uplift of the cold air in the south and the mountains prompts the convective cells on the spiral rain belt outside the typhoon to be triggered.Meanwhile,the enhancement of wind shear in the spiral rain belt outside the typhoon also plays a certain role in the occurrence and development of the strong convection.(4)The environmental field provided good driving force and water vapor conditions for the precipitation of typhoon maria.Under the influence of typhoon maria's core and outer spiral rain belt,heavy precipitation occurred along the coast of Fuzhou,Jianning region and Wenzhou region.The typhoon circulation organizes the scattered convection cells with low center of mass near the main core into blocks,and the abundant water vapor triggers the convection with the convergence line of surface wind field,the forced uplift of mountain range and the dense temperature gradient.The precipitation in Wenzhou region affected by the spiral rain belt outside the typhoon has obvious "train effect",and the convective cells have the characteristics of low center of mass and forward tilt.The bell-mouth topography in Wenzhou region makes the ground airflow have a strong convergence movement,forming a ground convergence line,with sufficient warm and wet airflow,triggering the convection and leading to the occurrence of heavy precipitation.