Effect of a Scale-Aware Convective Parameterization Scheme on the Simulation of Convective Cells-Related Heavy Rainfall in South Korea

Abstract

In this study, the effect of a scale-aware convective parameterization scheme (CPS) on the simulation of heavy precipitation in the gray-zone was investigated using the Weather Research and Forecasting (WRF) model. We performed WRF simulations with the Kain-Fritsch (KF) scheme (non-scale-aware), Multiscale Kain-Fritsch (MSKF) scheme (scale-aware), and explicit convection (i.e., no CPS). The MSKF scheme uses a scale-aware parameter that modulates the convective available potential energy (CAPE) timescale and entrainment process in the KF scheme as a function of the horizontal grid spacing. The results of this study show that WRF simulations using explicitly resolved convection lead to overestimations and erroneous precipitation locations in the gray-zone because the convection and atmospheric instability cannot be appropriately triggered and reduced. The CPS without scale-awareness in the gray-zone exaggerates the convection and distorts synoptic fields, leading to the erroneous simulation of heavy precipitation at high resolution. The MSKF scheme with scale-awareness improves the simulation of convective cells-related heavy rainfall by removing the atmospheric instability in the gray-zone, reducing the role of the CPS, and increasing the role of the microphysics parameterization scheme (MPS) with decreasing grid spacing. In addition, the results of sensitivity experiments show that reducing the CAPE timescale leads to the faster development of convective cells, whereas decreasing the entrainment leads to precipitation overestimation. The modulated parameters in the scale-aware MSKF scheme play a crucial role in balancing the effects of the CPS and MPS in the gray-zone.