Effects of Parameters Defining the Characteristics of Raindrops in the Cloud Microphysics Parameterization on the Simulated Summer Precipitation over the Korean Peninsula

The study examines the effects of parameters that define the characteristics of raindrops on the simulated precipitation during the summer season over Korea using the Weather Research and Forecasting (WRF) Double-Moment 6-class (WDM6) cloud microphysics scheme. Prescribed parameters, defining the characteristics of hydrometeors in the WDM6 scheme such as a(R), b(R), and f(R) in the fall velocity (V-R) - diameter (D-R) relationship and shape parameter (mu(R)) in the number concentration (N-R) - D-R relationship, presents different values compared to the observed data from Two-Dimensional Video Disdrometer (2DVD) at Boseong standard meteorological observatory during 2018 similar to 2019. Three experiments were designed for the heavy rainfall event on August 8, 2022 using WRF version 4.3. These include the control (CNTL) experiment with original parameters in the WDM6 scheme; the MUR experiment, adopting the 50th percentile observation value for mu(R); and the MEDI experiment, which uses the same mu(R) as MUR, but also includes fitted values for a(R), b(R), and f(R) from the 50th percentile of the observed V-R - D-R relationship. Both sensitivity experiments show improved precipitation simulation compared to the CNTL by reducing the bias and increasing the probability of detection and equitable threat scores. In these experiments, the raindrop mixing ratio increases and its number concentration decreases in the lower atmosphere. The microphysics budget analysis shows that the increase in the rain mixing ratio is due to enhanced source processes such as graupel melting, vapor condensation, and accretion between cloud water and rain. Our study also emphasizes that applying the solely observed mu(R) produces more positive impact in the precipitation simulation.