Evaluating Simulated Raindrop Size Distributions and Ice Microphysical Processes With Polarimetric Radar Observations in a Meiyu Front Event Over Eastern China

To better understand the characteristics of simulated raindrop size distributions (DSDs) and ice microphysical processes for convective systems in the East Asia monsoon region, a typical Meiyu event is simulated with the Weather Research and Forecasting (WRF) model using three two-moment bulk microphysics schemes in this study. The simulated microphysical characteristics are then evaluated using polarimetric radar observations and retrievals. Although the observed linear storm structures are well simulated in terms of their location, there are significant deviations regarding simulated polarimetric radar variables and DSD parameters when compared to the observations. Compared to radar retrievals, all the simulated low-level raindrops are found to have lower number concentration and larger mean sizes. To investigate the sources of the simulated DSD biases, vertical distributions of radar reflectivity and specific ice hydrometers (snow, graupel), as well as profiles of liquid/ice water contents from radar retrievals and simulations are further compared. In addition, variations about the occurrence frequency and transfer rate for four categories of ice processes (deposition, aggregation, riming, and melting) among the three schemes are analyzed. Results indicate that the overprediction of snow and graupel from riming processes is likely to be responsible for the production of extremely large raindrops at low levels.