Distinct diurnal characteristics of summer precipitation and underlying mechanisms in the Tibetan Plateau and surrounding basins

The climatological characteristics and mechanisms of diurnal variation in summer precipitation over the Tibetan Plateau and its adjacent basins (i.e., the Tarim Basin, Ganges Basin, and Sichuan Basin) are investigated using observational/reanalysis data and a high-resolution dataset from convection-permitting regional climate downscaling. The results indicate that the diurnal variations of precipitation are nearly out of phase between the central Tibetan Plateau and the surrounding basins. Precipitation in the main body of the plateau preferentially occurs in the afternoon-evening hours, primarily attributed to daytime solar heating induced enhancement of local convective instability and large-scale moisture convergence. In contrast, precipitation in the surrounding basins favors the midnight-early-morning period. The diurnal oscillation of the mountain-plain solenoid circulation, which is resultant from the elevated daytime solar heating and nighttime longwave radiative cooling along the topographical slope, is identified as a crucial mechanism governing the diurnal precipitation pattern in all the basins. Additional factors contributing to the midnight-early-morning precipitation include the nocturnal strengthening of the low-level southwest monsoon flow for the Ganges and Sichuan Basins, as well as propagating convection originating from the eastern plateau and leading to a diurnal phase lag in the Sichuan Basin. These results further enhance our knowledge and understanding of the complex diurnal precipitation cycle and associated physical processes over the Tibetan Plateau and nearby regions.