The Microphysical Properties of Convective Precipitation over the Tibetan Plateau by a Subkilometer Resolution Cloud-Resolving Simulation

The microphysical properties of convective precipitation over the Tibetan Plateau (TP) are unique because of the extremely high topography and special atmospheric conditions. In this study, the ground-based cloud radar and disdrometer observations as well as high-resolution WRF simulations with the Chinese Academy of Meteorological Sciences (CAMS) microphysics and four other microphysical schemes are used to investigate the microphysics and precipitation mechanisms of a convection event on 24 July 2014. The WRF-CAMS simulation reasonably reproduces the spatial distribution of 24-h accumulated rainfall, yet the temporal evolution of rain rate has a delay of 1-3 hours. The model reflectivity shares the common features with the cloud radar observations. The simulated raindrop size distributions demonstrate more of small- and large-size raindrops produced with the increase of rain rate, suggesting that changeable shape parameter should be used in size distribution. Results show that abundant supercooled water exists through condensation of water vapor above the freezing layer. The prevailing ice crystal microphysical processes are depositional growth and autoconversion of ice crystal to snow. The dominant source term of snow/graupel is riming of supercooled water. Sedimentation of graupel can play a vital role in the formation of precipitation, but melting of snow is rather small and quite different from that in other regions. Furthermore, water vapor budgets suggest that surface moisture flux be the principal source of water vapor and self-circulation of moisture happen at the beginning of convection, while total moisture flux convergence determine condensation and precipitation during the convective process over the TP.