Effect of Underlying Surface on the Formation and Evolution of Hail Cloud

Using the mesoscale model WRF (Weather Research and Forecasting), a severe hailstorm that occurred in Beijing on 31 May 2005 was simulated and compared with the observed radar echo, the hailstorm track, and the hail fall area, to investigate the effect of the underlying surface, such as urban areas or agricultural land, on the hailstorm. The results show that the sensible heat flux shows a clear increase due to the urban heat island effect. This increase in the flux is favorable for the development of hail clouds and the formation of larger hailstones, resulting in an increase in the surface-accumulated hail fall; however, its influence on the track of the hail clouds is less significant. In contrast, agricultural land surfaces have a larger latent heat flux and higher evaporation, which is favorable for the formation of a large amount of smaller hailstones, and results in reduced hail water content in the clouds. The surface-accumulated hail fall therefore decreases over these areas due to the weakening effect of agricultural land surfaces on hail clouds.