A Preliminary Study On The Mesoscale Characteristics Of Heavy Rain In The Warm Area Of ??the Jiangnan Area And The Cause Of Precipitation

The definition of warm sector rainstorms was first put forward by Mr.Huang Shisong.Research and operational applications mainly concentrated in South China.However,the analysis of the extremes of torrential rain on July 21 th in Beijing in 2012 shows that the process was consisted of warm sector and frontal precipitation.Due to insufficient understanding and limited predictive ability of global model in warm sector rainstorm,the beginning time of forecasting was late and intensity was underestimated.Therefore,those warm sector rainstorms outside of South China are also worth studying,especially over the South of Middle and Lower Reaches of the Yangtze River where torrential rains happened frequently.First,the definition of warm-sector rainstorms over the South of Middle and Lower Reaches of the Yangtze river is given,and they can be divided into four types: the Warm Shear(WS),the Pre-Frontal(PF),the Western Pacific Subtropical High(WPSH)and the Strong Southwest Jet(SSWJ)by the synoptic situations.By using the conventional and non-conventional observation data such as the hourly precipitation data of Automation Weather Station(AWS)from May to September during 2010-2016,the temporal,spatial distribution of warm-sector rainstorms,the nature of precipitation and the characteristics of the mesoscale rain clusters are studied by statistics.Besides,based on NCEP FNL Opearational Global Analysis data and the technology of mesoscale analysis,four kinds system configuration are built and the formation of warm-sector rainstorms is also analyzed preliminary.The main conclusions are as follows:(1)The warm sector rainstorms often manifest as the long life and moving mesoscale rain clusters,when it passes through inhomogeneous land surfaces such as mountains,rivers and lakes,the intensity often increases and moves slow,which causes the dispersive local heavy rainfall.The WS precipitation mainly locates in the mid-west with wide range of precipitation,the strongest intensity and the most obvious extreme.The PF one is mostly concentrated in the middle,strong and has a certain degree of extreme.The WPSH one often occurs in the mid-east with weak intensity.The SSWJ one primarily appears in the west.(2)The WS and SSWJ precipitation are dominated nocturnal,and the WPSH one is mainly concentrated in the afternoon,while the diurnal variation of the PF one is not obvious.(3)The warm sector rainstorms consist of stable and convective precipitation,and the heavier daily rainfall is,the more obvious convective precipitation is.(4)With the high humidity,unstable energy accumulation and other favorable background,the WS,the PF and the WPSH are mostly generated by boundary layer(ground)mesoscale convergence lines,coupled with the place of the coupling of upper and low-level jet.The SSWJ is generally formed on the mesoscale wind speed fluctuation on the low-level jet stream and ground mesoscale convergence lines.Then,by using the radar combined reflectivity factor puzzle data,and the identification and classification criteria of the Mesoscale Convection System(MCS),the organizational forms of the MCSs in the warm sector rainstorms of the study area is typed.Besides,the temporal,spatial distribution,disrtibution and transitions of organizational modes of the MCSs in the primary stage and the organizational process are counted.The main conclusions are as follows:(1)The MCSs in the four kinds of warm sector rainstorms can be divided into three types: the cellular,the linear and the non-linear.The cellular MCS can be subdivided into two types: Individual Cell and Clusters of Cells;the linear ones can be subdivided into six types: Embedded Line,Broken square Line,Trailing Stratiform,Leading Stratiform,Parallel Stratiform,and Non-stratiform Line;the non-linear ones can be subdivided into 4 types: Embedded Non-line,Broken square Non-line,Trailing Stratiform Non-line and Leading Stratiform Non-line.(2)The organizational modes of MCSs at primary,which cause warm sector rainstorms are mostly the Clusters of Cells,and primarily concentrated in the west and mid-east.MCSs in the west are often triggered at night,while the others are in the daytime.(3)It may be the reason that MCS in the WS and the PF have longer organization time why their precipitation have greater intensity and longer duration.(4)The non-linear and the linear MCSs are almost the same proportion in the four kinds of warm sector rainstorms.The linear MCSs often occur in the middle transitional process,and the proportion of the Embedded Line is much higher than other types;The non-linear ones often appears in the final form,and the Embedded Non-line accounts for the highest proportion,followed by the Trailing Stratiform Non-line.