Cloud microphysical properties and precipitation over the Tibetan Plateau are unique because of the high terrains, clean atmosphere, and sufficient water vapor. With dual‐polarization precipitation radar and cloud radar measurements during the Third Tibetan Plateau Atmospheric Scientific Experiment, the simulated microphysics and precipitation by the Weather Research and Forecasting (WRF) model with the Chinese Academy of Meteorological Sciences (CAMS) microphysics and other microphysical schemes are investigated through a typical plateau rainfall event on 22 July 2014. Results show that the WRF‐CAMS simulation reasonably reproduces the spatial distribution of 24 h accumulated precipitation but has limitations in simulating time evolution of precipitation rates. The model‐calculated polarimetric radar variables have biases as well, suggesting bias in modeled hydrometeor types. The raindrop sizes in convective region are larger than those in stratiform region indicated by the small intercept of raindrop size distribution in the former. In addition, the warm rain processes generate heavier precipitation than the cold rain processes do over the rainfall centers during weak convection period. The sensitivity of precipitation to perturbing the warm rain microphysical processes show that doubling droplet condensation increases precipitation significantly and produces the best area‐averaged rain rate, suggesting biases in thermodynamics in the baseline simulation. Halving raindrop evaporation results in an increase in weak rainfall areas along with a warmer subcloud layer. Increasing the initial cloud droplet size causes the rain rate reduced by half, an opposite effect to that of increasing droplet condensation.

The microphysical properties of convective precipitation over the Tibetan Plateau 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 Weather Research and Forecasting simulations with the Chinese Academy of Meteorological Sciences microphysics and four other microphysical schemes are used to investigate the microphysics and precipitation mechanisms of a convection event on 24 July 2014. The Weather Research and Forecasting‐Chinese Academy of Meteorological Sciences simulation reasonably reproduces the spatial distribution of 24‐hr accumulated rainfall, yet the temporal evolution of rain rate has a delay of 1–3 hr. 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 Tibetan Plateau.

Entrainment rate is a critical but highly uncertain quantity in convective parameterizations; especially, the effects of environmental relative humidity on entrainment rate are controversial, or even opposite, in different studies. Analysis of aircraft observations of cumuli from the Routine AAF (Atmospheric Radiation Measurement [ARM] Aerial Facility) Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations (RACORO) and Rain in Cumulus over the Ocean (RICO) field campaigns shows that entrainment rate is positively correlated with relative humidity. Physical analysis shows that higher relative humidity promotes entrainment by reducing buoyancy in the cloud cores and by weakening downdrafts near the cloud cores. The reduced buoyancy in the cloud cores and weakened downdrafts surrounding the cores further reduce updrafts in the cloud cores; the cloud cores with smaller updrafts are more significantly affected by their environment, resulting in larger entrainment rate. The relationship between entrainment rate and relative humidity is consistent with the buoyancy sorting concept widely used in convection parameterizations. The results provide reliable in situ observations to improve parameterizations of entrainment rate.

Entrainment‐mixing mechanisms significantly affect cloud droplet number concentration, radius, and spectral shape. Quantitative examination of entrainment‐mixing effects on cloud droplet spectral width is lacking. This study examines the effects of entrainment‐mixing processes on cloud microphysics by 12,218 different setups, each simulated 10 times using the Explicit Mixing Parcel Model (EMPM) driven by the observational data from the Third Tibetan Plateau Atmospheric Scientific Experiment (TIPEX‐III) campaign. Parameterizations of entrainment‐mixing mechanisms are developed by relating homogeneous mixing degree to transition scale number that depends on the dissipation rate and droplet evaporation time scale. The correlation between relative dispersion of cloud droplet size distribution and homogeneous mixing degree changes from negative to positive with the decreasing homogeneous mixing degree. The different relationships are closely related to the competition between complete and partial droplet evaporation and the number concentration of small droplets, which are quantitatively described by two newly introduced dimensionless numbers. The competition is significantly affected by relative humidity and mixing fraction of entrained air as well as turbulence dissipation rate, but not much by cloud droplet number concentration. Especially, when relative humidity and dissipation rate are high, there is only a negative correlation. This study sheds new light on generalizing the homogeneous/inhomogeneous concept by considering relative dispersion and also provides parameterizations of entrainment‐mixing processes and relative dispersion for atmospheric models.

In this study, the effects of vertical wind shear (VWS) on the raindrop size distribution in tropical cyclone are investigated, based on the theoretical analyses that intense VWS, which commonly appears in the lower layers of tropical cyclones, can enhance the collisional breakup of raindrops. This is achieved by comparing the numerical sensitivity experiments of Typhoon Nida (2016) using Weather Research and Forecasting model against the polarimetric radar and disdrometer observations. In the control run with the default Morrison microphysics, unrealistic large raindrops are produced with excessively large differential reflectivity and heavier precipitation. An obvious decrease of raindrop size is present when the constant value of cloud droplet number concentration reduces from 250 to 30 cm⁻³ (NC30), leading to more comparable microphysics characteristics with the observations due to the enhancement of autoconversion rate from cloud droplets to raindrops; however, some unrealistic large‐sized raindrops still exist. A semiempirical raindrop collection/breakup parameterization is further proposed in NC30_WS run by modifying the threshold diameter of raindrops at which breakup occurs as a function of VWS. The certain improvements of simulating raindrop size distribution and precipitation in Typhoon Nida are present in NC30_WS run, owing to the efficient collisional breakup and the induced stronger raindrop evaporation cooling. Our results indicate that the combined effects of reasonable cloud droplet numbers as well as reliable raindrop breakup parameterization are pronounced and highlight the impacts of VWS on raindrop size distribution, which should be involved in current microphysical schemes to forecast the TCs more accurately.

The Weather Research and Forecasting (WRF) model with Large Eddy Simulation was employed to investigate a local‐scale convective precipitation event at Naqu (altitude of 4.5 km) over the central Tibetan Plateau (TP) on 24 July 2014. The WRF‐LES simulations with horizontal grid spacing of 200 m (CTRL) basically reproduced the rainfall pattern and evolution process compared to the observations. Five sensitivity experiments including removal the hills in east of Naqu (TER), decrease or increase of surface sensible heat flux (HFX0.67, HFX1.5), and surface latent heat flux (QFX0.67, QFX1.5) were implemented, respectively. Results show that the increase of surface heat flux and the eastern hills both enhanced the convection, which was triggered by the low‐level wind convergence. The QFX0.67 simulated the weakest precipitation among six runs, and the QFX1.5 simulated the earliest and strongest convection due to the enhanced atmospheric instability. It is found that the HFX0.67 caused the earlier convection initiation than CTRL and HFX1.5 owing to the lowest lifting condensation level and wettest low troposphere in it. Over the flat terrain in west of Naqu, weak convection was mostly affected by the surface heat flux. The product of 4.8 km wind convergence and difference between 7 km and 4.8 km equivalent potential temperature (>2 × 10⁻² K/s) can partly indicate the development of low‐layer turbulence and the subsequent convection in free atmosphere. In addition, water vapor condensation (extending to 10 km) and raindrop evaporation (below 6 km) were two key phase‐change microphysical processes during the convective period even the quite low 0°C layer (∼6.5 km) over TP.