Factors Influencing Diurnal Variation Of Cloud And Precipitation In the Yushu Area, Tibetan Plateau

Using data from cloud radar, ground observations and ERA5 reanalysis data, factors influencing nighttime precipitation during summer in the Yushu area of the Tibetan Plateau (TP) are investigated. The cloud top height (CTH), cloud base height (CBH) and liquid water content (LWC) are compared between the non-precipitating days and precipitating days. The results show that the average CTH during precipitating days over Yushu is below 10 km above ground level (hereafter AGL) in the daytime, while it is more than 10 km AGL at night with the maximum at 23 Beijing Standard Time (BST, = Coordinated Universal Time + 8 hour). The CBH is in phase with the dew-point spread. The precipitation intensity and CTH is in phase with the LWC. The hourly averaged precipitation intensity and convective available potential energy (CAPE) in ERA5 reach the maximum at 21 BST, which is 3 hours ahead of the observations. There is downward motion flow at noon during non-precipitating days, while there is upward motion flow at night during the precipitating 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 middle level of the atmosphere, is accompanied by subtropical westerly jet in the upper level. The difference of horizontal wind speed between the level of 200 hPa and 500 hPa is positively related to the LWC, making contribution to the formation of upper-level clouds