Factors Influencing Diurnal Variations of Cloud and Precipitation in the Yushu Area of the Tibetan Plateau

Using the cloud radar,ground observations,and ECMWF Reanalysis v5(ERA5)data,we investigate the factors influencing nighttime precipitation during summer in the Yushu area of the Tibetan Plateau(TP).The cloud top height(CTH),cloud base height(CBH),and liquid water content(LWC)are compared between non-precipitation and precipitation days.The results show that the average CTH on precipitation days in Yushu is below 10 km above ground level(AGL)in the daytime,whereas it exceeds 10 km AGL at night,with the maximum at 2300 BT(Beijing Time).The CBH is in-phase with the dewpoint spread.The precipitation intensity and CTH are in-phase with the LWC.The hourly averaged precipitation intensity and convective available potential energy in ERA5 reach their maximums at2100 BT,which is 3 h ahead of their observed counterparts.There is descending motion in the mid day on non-precipitation days,whereas there is ascending motion at night on precipitation days.In addition,the horizontal wind direction in the lower level(below 5000 m)shows clockwise rotation from morning to night.Wind shear occurs in the mid level of the atmosphere,accompanied by a subtropical westerly jet in the upper level.The difference in horizontal wind speed between 200 and 500 hPa is positively related to the LWC,thereby contributing to the formation of upper-level cloud.