The Circulation Characteristics And Forecast Of Heavy Rainfall In The Jianghuai Region

Based on historical case data of regional heavy precipitation process and 1981-2015 daily precipitation data of 2474 observational stations in China,by defining extreme rainfall threshold with the percentile method,extreme precipitation model is built,the extreme rain patterns are classified and the typical circulation patterns are refined.And then the classification of the regional heavy rain patterns are done taking the corresponding circulation patterns of the extreme rain as targets with an analogue method expanding from the daily extreme rainfall events to the heavy rain events.Patterns of the heavy rainfall have similar spatial distribution to the extreme rainfall,apart from the rainfall amount of the heavy rainfall is less than the extreme rain patterns.Further,the circulation characteristics of heavy rain cases in Jianghuai region are investigated,and the results of the classification are quantitatively diagnosed.The conclusions are as follows:(1)During the six extreme heavy rainfall,the precipitation in the Jianghuai region is distributed as a belt,and the large value center is basically located in the eastern coastal area.In the six extreme process,the corresponding high and low level circulations have obvious similarity,which is beneficial to the formation of strong precipitation.(2)The cosine similarity method is applied to extend the extreme heavy rain pattern to a regional heavy rainfall case.The spatial distribution of each type of heavy rainfall is similar to the spatial distribution of extreme rain.Remarkable features are appeared in Asian area from low to high latitudes during the day from leading 10d to 0d at 500hPa,and obvious differences can be seen between the different pattems.From the prophase of heavy rainfall,both ? and?have meridional type circulation,? appears a big low vortex.The western Pacific subtropical high(WPSH)of Type ? and type ? slowly develop westward,and WPSH of type?is relatively weak.In the Jianghuai area,divergence in upper level and convergence in low level leads to the rising movement.However,the systems move slowly for all the three patterns,and Jianghuai is in the control of the relatively low system between the two highs on both sides during the day heavy rainfall occurring,which is prevail to the occurring of heavy rainfall over this region.(3)There is a high correlation between calculated and measured circulations and precipitation.Therefore,the method can be used to predict the heavy rainfall tentatively,and the evolution of the corresponding circulation at different levels is taken as the basic type to revise the model heavy rainfall forecast.(5)Based on the cosine similarity method and the similar area R,the regional strong precipitation model library was established for the independent prediction test of precipitation in the summer of 2016,and it was compared with the precipitation forecast which was directly given by two models:T639 and ECMWF.The results show that the accuracy of prediction from high to low is similarity coefficient R(SCR),cosine similarity coefficient(CSC),EC,T639,respectively.The prediction accuracy of similar method is higher than that of mode output when it is used for more than 5 days.In short term forecast,the results of several methods have little difference.At the same time,the prediction based on the predicted circulation of ECMWF is compared with that of NCEP/NCAR reanalysis data,and the prediction accuracy is not very different.