Effects of bulk ice microphysics on the simulated monsoonal precipitation over east Asia

This study examines the effects of bulk ice microphysical processes on the simulation of monsoonal precipitation in summer over east Asia, centered over Korea. The mixed phase microphysics scheme of the WRF-Single-Moment-MicroPhysics class 5 (WSM5) is implemented into the fifth-generation Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model (MM5). The performance of the WSM5 scheme is compared to that of Reisner's mixed phase scheme, that is, the MM5-Single-moment-Microphysics class 5 (MSM5). Together with looking at the impact of ice microphysics, the importance of the sedimentation of falling ice crystals on simulated rainfall events is investigated. The same sensitivity experiments are extended to a 2-month-long simulation of the east Asian summer monsoon. It was found that the new microphysics in the WSM5 scheme produces a more realistic vertical distribution of condensates. For a locally developed heavy rainfall event over Korea, the impact of revised ice microphysics is significant. The WSM5 scheme simulates more (less) precipitation in the south (north), compared with that of the MSM5 scheme, by stabilizing the air columns in the rainfall area, leading to a better agreement with the observed precipitation. By contrast, ice sedimentation becomes more important for those cases of heavy rainfall, associated with a mobile surface cyclone system, accomplished by suppressing large-scale bias through a realistic ice cloud/radiation feedback. The sedimentation of cloud ice is found to be crucial to the successful simulation of monsoonal precipitation and large-scale features within the east Asian summer monsoon.