Influence of the terminal velocity of graupel on the simulation of a convective system over Beijing

Abstract

The terminal velocity of graupel (Vg) affects the development of strong convective systems, but there are large uncertainties in the description of Vg in numerical models. We examined the effects of Vg on the structure and evolution of a strong convective system in Beijing using the Advanced Research Weather Research and Forecasting Model (ARW-WRF). Multiple simulations were performed to test the sensitivity of the model to different fitting equations of Vg in the WDM6 microphysics scheme. We found that a larger value of Vg significantly increased the precipitation rate. With respect to the distribution of hydrometeors, a larger value of Vg reduced the centroid and peak value of snow, graupel and cloud water above the freezing layer, while the centroid of rainwater decreased and the peak value increased. This promoted the conversion of ice particles into rainwater. As a result of the complexity of heat exchange in cloud microphysical processes, the effects of Vg on the heat budget of precipitation particles within clouds have strong nonlinear characteristics.