Study On The Verification And Impact Factors Of Quantitative Precipitation Forecasts In Summer In China Based On The Ensemble Forecasts

The research of Quantitative Precipitation Forecasts(QPF)is very important.In order to improve the ensemble forecasts in China,the verification of QPF is significant.The data is collected from ECMWF and CMA,ranging from 2010 to 2016.Structure,Amplitude and Location(SAL)is used to assess the forecasts from EC and CMA.SAL is used to find the differences between the forecasts for precipitation in South China with other regions,including Middle and lower reaches of the Yangtze River,North China and Northeast China.According to precipitation forecasts verification,several conclusions are drawn as follows.(1)For EC and CMA models,the precipitation forecasts are assessed by SAL.Then positive values of S occur a lot,which means too large precipitation objects,too flat objects,or a combination of these factors.During the four tested regions,the error for flat forecasts in South China is the biggest.(2)Most of the flat cases of forecasts are due to too large and too flat objects.The number of the flat cases which are only due to area is second.All in all,area is the most important for the forecasting error.The forecast for South China is also like that.(3)On the section of amplitude,EC forecasts perform strong in South China and Northeast China,while perform weak in the other two regions.CMA forecasts perform strong in South China,Middle and lower reaches of the Yangtze River and Northeast China,while perform weak in North China.(4)On the section of location,EC forecasts performs southwest to the observation most,northwest to the observation second.EC forecasts perform significantly to the west.CMA forecasts is similar to EC forecasts,while T639 forecasts performs northwest and northeast to the observation most in South China,performs southwest and southeast to the observation most in North China and Northeast China.(5)For the three components S,A and L,EC and CMA perform best on L,A is the second and S is the last.(6)Compared with T213 forecasts,T639 forecasts improve in structure and location.(7)Ensemble forecasts perform better on amplitude than control forecasts.(8)Compared with SAL,TS method is more effective in assessing structure and location of rain belts,and has weaker ability to assess amplitude.During the four tested regions,the forecasts in South China make the biggest error in S and L.area of the rainfall is the most affective factor in South China than the other three regions.So the QPF in South China is the most difficult.It's cruel to study the impact factors,such as the leading weather systems for the heavy rain forecasts in South China.Then by studying the ERA-interim reanalysis data and comparing the bad and good EC member groups,these conclusions are drawn as follows:(1)The southwest wind from South China Sea Monsoon,the western Pacific subtropical high,the cold air from the north and the cold air from westerly trough are affective weather systems for this event.(2)It's the the forecast of the southwest wind makes the biggest difference.One reason for the difference is the difference on the forecast of the southwest wind from South China Sea Monsoon,the other reason for the difference is the difference on the forecast of the west extension and the strength of the western Pacific subtropical high.On conclusion,the leading affective weather systems for the heavy rain event are the southwest wind from South China Sea Monsoon and western Pacific subtropical high extension.