A Modified Parameterization of the Buoyancy Production of Turbulent Kinetic Energy to Improve the Transition to Deep Convection

The Weather Research and Forecasting model version 4.3.3 with an eddy-diffusivity mass-flux (EDMF) scheme, which is a blend of the Mellor–Yamada–Nakanishi–Niino scheme including a partial condensation scheme and a mass-flux scheme, is used to forecast a quasi-stationary band-shaped precipitation event that occurred over the Hokuriku region on 12-13 July 2023. However, the original model does not satisfactorily reproduce the heavy precipitation over the region at a horizontal resolution of 5 km. Our companion papers suggested that improving the parameterization of the buoyancy production of turbulent kinetic energy (TKE) is necessary for such a coarse-resolution model to accurately simulate the transition from shallow to deep convection that triggers heavy precipitation. In this study, its parameterization in the EDMF scheme is modified to divide it into two contributions from the partial condensation and mass-flux schemes. The results show that although the modified model predicts the band-shaped distribution of precipitation with a westward bias, it simulates the timing and intensity of heavy precipitation reasonably well. This study presents the modified parameterization of the TKE buoyancy production and demonstrates that a modification of its parameterization can improve the prediction of heavy precipitation.