Contribution of shallow convection to the localization of a band shaped area of heavy precipitation on 4 July 2020

Abstract

On 4 July 2020, a quasi-stationary band-shaped area of heavy precipitation occurred near the center of Kyushu, Japan. The contribution of shallow convection to the localization of the precipitation area is examined using the Weather Research and Forecasting model. Two turbulent transport schemes, the Yonsei University scheme and the Mellor–Yamada–Nakanishi–Niino (MYNN) scheme, are selected. Simulations are performed for a 5-km horizontal resolution domain (SIM1) and a 1-km horizontal resolution domain nested within the 5-km resolution domain (SIM2). The results show that SIM1 predicts a more northerly bias than a radar/raingauge-analyzed precipitation area but provides a relatively small bias for the MYNN scheme, and SIM2 predicts the analyzed precipitation area reasonably well for both schemes. They also suggest that the improvement in SIM2s is due to the transition from shallow to deep convection upwind of the southwesterly wind, and the MYNN scheme with a partial condensation scheme in SIM1 reasonably simulates the growth of shallow convection by parameterizing the buoyancy production of turbulence associated with cloud formation. It is expected that the accurate prediction of shallow convection can improve the reproduction of the location of heavy precipitation areas.