A Study On The Spatial And Temporal Characteristics Of Atmospheric Rivers In North China And Their Influence On Heavy Rainfall

Based on the atmospheric river(AR,for short)data set AR Reanalysis Databases V1.0,we analyzed the temporal and spatial characteristics of the AR and the spatial characteristics of anomalous years of AR in North China in the past 35 years.Moreover,we carried out the thermodynamic and kinetic diagnosis and analysis of one rainstorm in North China under the background of the AR on May 15-16,2018.We have studied the structure of AR in depth,and proposed a weather conceptual model of rainstorm under the background of AR.The conclusions are as follows:ARs in North China can occur in all seasons of the year.The AR is directly related to the occurrence of rainstorm in North China.In the past 35 years,the AR and rainstorm both increase month by month from January to July,reach a peak in July,and then decrease.The process of AR is consistent with the process of rainstorm in North China.The AR in North China has the characteristics of large inter-annual variation.The frequency of AR and rainstorm days are higher in spring and summer,but lower in autumn and winter.The maximum values of both occur in July,and the least three months occur in December,January and February.From low latitudes to high latitudes,the ARs are mainly distributed in a band from southwest to northeast.The ARs play an important role in the transportation of water vapor in the atmospheric circulation.The large value center of the rainstorm day surrounds the large value center of the AR.The frequency of AR has an obviously reduced tendency from low latitudes to high latitudes,from coastal to inland.When obstructed and forced uplift by the topography,the AR can trigger rainstorm.In the high-frequency geographic areas where ARs appear in years with more ARs,the Western Pacific Subtropical High and the outer southwest airflow affect the North China.In years with fewer ARs,the Subtropical High retreats eastward to the ocean,and there is no obvious southwest wind.The difference in the circulation pattern between the years with more ARs or less is mainly located in the middle and lower layers,the upper layers are with little difference,because they are dominated by westerly air flow.The water vapor and thermal condition of years with more ARs are more beneficial to the occurrence of ARs and rainstorms than those of years with less ARs.We have systematically analyzed in detail the rainstorm in North China under the influence of a typical AR on May 15-16,2018.The conclusions are as follows:The heavy rainstorms in the relatively dry seasons in North China are directly related to the appearance of the ARs.During this process,the AR was stronger than usual,it extended from South China Sea through North China to Japan and cooperated with other weather systems to produce this spring rainstorm in North China.Based on this example,we have summarized the weather conceptual model of rainstorm in North China under the background of AR.