Weather Background Types And Numerical Simulation For The Extreme Precipitation Occurred Over The Dabie Mountain Region

Dabie Mountain is located at the junction of Anhui,Hubei and Henan provinces.Its average altitude is about 500-800 m,and its highest peak,Baimajian,reaches 1777 m.It is the watershed between the Huaihe River system and the Yangtze River system,and its complex terrain often leads to large changes in the temporal and spatial distribution of precipitation,forming more frequent areas of extreme precipitation weather events in some areas.The weather background for extreme precipitation occurred over the Dabie Mountains during2008-2014 is classified using the self-organizing map(SOM)method,based on the CMORPH precipitation products merged with AWS observations in China and the NECP reanalysis data.Three major types of weather background are identified according to the different prevailing airflows:strong southwest airflow(type I),airflow over the northwest side of western Pacific subtropical high(type II),and strong southerly airflow(type III).The extreme precipitation of type I and type II primarily occurred in summer,from June to August and from July to September respectively.While the extreme precipitation of type III mainly occurred in spring from March to June or in autumn from October to December.The positions of the Dabie Mountains relative to the extreme precipitation and the prevailing airflows are investigated,and the results show that:(1)for type I,the extreme precipitation is mainly associated with heavy upslope rainfall due to high mid-level moisture and strong upslope lifting;(2)the lower mountains over the northeastern Dabie Mountains can cause extreme precipitation of type II when the western Pacific subtropical high moves further northward and westward;(3)the strong southerly airflow in type III can make the extreme precipitation occur between the south side of the Dabie Mountains and the upstream mountains.In this paper,the typical extreme precipitation weather events of the weather types are further selected,numerical simulation studies are carried out to analyze the type commonalities and individual characteristics of the extreme precipitation weather events.The weather environment of each of the events generally reflect the average environmental characteristics of the corresponding weather type,the simulated heavy precipitation area is also basically consistent with the average extreme precipitation area of the corresponding weather type.The particularity of the typical cases is that the evolution of heavy precipitation is related to the movement and change of specific weather systems and the occurrence and development of smaller-scale weather disturbances.The typical case of type I includes the interaction between the middle-level cyclone disturbance and the main body of the Dabie Mountains,the typical case of type II contains the interaction between the southwest warm airflow and the northern cold airflow over the northwest-extended ridge of the Dabie Mountains,and the typical case of type III holds reasonable configuration of the southwest warm airflow between the Dabie and Huang Mountains.The particularity of individual cases makes the specific weather disturbance interact with the terrain of the Dabie Mountains at different locations within the favorite extreme precipitation area of the correspondng type,resulting in the occurrence of extreme precipitation weather events.