Analysis On Structural Characteristics Of Landfalling Typhoon With Extreme Precipitation

Resulting in extreme precipitation landing typhoon is the difficult problem in the study of typhoon science because of its disastrous,wide range of effects and strong persistence.In this paper,we focus on the extreme precipitation landing typhoon.First,we analyze the environmental background characteristics of this kind of typhoon,and then select the typical example typhoon Morakot(2009)to carry out high-precision numerical simulation experiment.We successfully reproduce the characteristics of the typhoon intensity,path and precipitation distribution,and carry out a series of sensitive tests to compare and analyze the evolution and structural variation of convective rainband and typhoon eyewall directly causing precipitation.In this paper,82 typhoons which were landed Taiwan Island were screened out from the typhoon in the Northwest Pacific for nearly 15 years,and the path was divided into four types.The extreme precipitation characteristics of the typhoon with the largest number of cases were selected,and 12 extreme precipitation landed typhoons were found in Taiwan.The analysis shows that such typhoons have similar environmental background field characteristics.Typhoon often develops in the monsoon gyre.During the landing period,the southwest side of Taiwan is strong southwest airflow,and the moving speed is slow.When the typhoon landed in Taiwan,the southwest airflow with the typhoon northwest airflow formed a strong convergence zone,and the strong water vapor convergence in the convergence zone was favorable for the occurrence of precipitation and the development of the convective rainband.The development process of the typhoon Morakot was simulated with the high value of WRF(V3.5),and three sets of underlying surface sensitivity test were carried out.The study shows that under the combination of typhoon circulation,Taiwan terrain and southwest airflow,the typhoon spiral rainband develops into a special east-west linear convective rainband,which is the direct manufacturer of extreme precipitation.Taiwan terrain is the key to the formation of such rainband:induced lifting rainfall to increase rainfall,change the environmental field humidity contrast,conducive to linear convective rain belt organization.From the vertical structure,this rainband and other types of rainband in the typhoon are different,showing the vertical stretch,strong scroll,rising speed characteristics.When the height of the terrain is reduced,the organization of the rainband is weakened,and when the mountain becomes flat or ocean,the east-west linear convective rainband disappears and the precipitation is drastically reduced.By comparing the simulation test with the sensitivity test,the causes of the change of the eyewall structure after the typhoon landing are obtained.The action of the terrain causes the tangential wind structure of the eyewall to be loose,mainly as the tangential wind of the eyewall is obviously reduced,especially on the west side of the eyewall.Typhoon warm heart structure is destroyed,mainly due to the secondary circulation of the typhoon north side weakened,making the cold air invasion typhoon core.