| Based on the station observation,CloudSat satellite observation and reanalysis data combined with WRF model,this paper analyzes the basic characteristics of persistent rainfall events(PREs)and the role of cloud radiation processes in the middle and lower reaches of the Yangtze River(MLYR)during the Meiyu period from 1979 to 2020.The main conclusions are as follows:(1)The precipitation during Meiyu period in MLYR are mainly characterized by PREs,which is divided into persistent heavy rainfall events(PHREs)and ordinary persistent rainfall events(OPREs)according to precipitation intensity.It is found that the PHREs contributes about 50% to the total precipitation during the Meiyu period.When PHREs and OPREs occur,both high and low circulation are conducive to the occurrence and development of precipitation in MLYR,but there is a big difference in the circulation situation between the two events.When PHREs occurs,the Western Pacific subtropical high is to the west and stronger,the subtropical westerly jet in East Asia is stronger;While OPREs occurs,the disturbance wave train propagating along the jet axis is more obvious.(2)When PREs occurs,the south of the rain area is dominated by high clouds,and the rain area is dominated by medium and low clouds.The clouds near the Meiyu front mainly include altocumulus,stratocumulus and cumulus,and the deep convective cloud is located on the south side of the Meiyu front.The cloud cover tilted northward with the decrease of height,and the anomaly of cloud radiation effect(CRE)was much stronger than the anomaly of average Meiyu CRE.The total effect of cloud radiation influence was the cooling effect in the MLYR,and the cooling effect of PHREs’ cloud was stronger than that of OPREs’ cloud.(3)In order to clarify the evolution process of precipitation,the three days before the occurrence of PREs are defined as dry phase,while the duration of PREs are defined as wet phase.The time series variation of cloud cover in each layer during the whole precipitation process is basically consistent with that of precipitation,but have great differences in the dry and wet phases.Compared with the dry phase clouds,the wet phase clouds in the north side have a more cooling effect,and the south side clouds have a heat effect.When PREs occurs,both the north and south sides of the Meiyu front are controlled by the warm advection.However,the cooling effect of the radiative forcing of the middle and low clouds on the north side offsets the warm advection,which cooling the region.While the high clouds and warm advection in the south side increase the temperature.These two processes made the temperature difference between the two sides of the Meiyu front increases significantly,maintain and enhance the Meiyu front,and make the precipitation continue.(4)Simulation results of the PHREs from July 8 to 17,2010 showed that WRF model can well simulate the main heavy precipitation centers of PHREs,but there is a deviation of the magnitude of precipitation.The low base cloud height and thicker clouds in the model simulation results in the cooling effect of clouds in the north of Meiyu front and the warming effect of clouds in the south of Meiyu front,which strengthen the Meiyu front,and cause more simulated precipitation.This simulation further verifies the influence of cloud radiation process on PREs,and also provides a reference for the improvement of numerical model. |
