A Scheme to Suppress Spurious Convection by Assimilating the "Zero" Column Maximum Vertical Velocity

Abstract

AbstractSuppressing spurious precipitation is one of the key issues in numerical weather prediction. To thoroughly suppress spurious convection, it is necessary to both inhibit the development of convection in false convection areas and weaken the heat and momentum exchange between false convection areas and other surrounding regions. In this study, a scheme to suppress spurious convection through cyclically assimilating the "zero" column maximum vertical velocity (wmax) using the ensemble square root filter (EnSRF) method is proposed. The "zero" wmax is the average wmax over the no‐rain echo region in the background field which is normally close to 0 m s−1. Two convective events that exhibit different characteristics are studied. The results show that the assimilation of "zero" wmax can suppress the upward motion and reduce the water vapor and hydrometeors of the background field in the false convection region, which can effectively suppress the development of spurious convection. In addition, the scheme can reduce the water vapor transport from surrounding areas to the spurious convection region and weaken the cold pool on the ground, which is not conducive to the regeneration and maintenance of false convection. The forecasts of reflectivity and precipitation show that the assimilation of "zero" wmax can effectively suppress either the strong false convection band or the weak spurious convection surrounding the true rain band and can decrease the false alarm rate of reflectivity and precipitation.