下垫面对雹云形成发展的影响

利用中尺度模式WRF(Weather Research and Forecasting)对2005年5月31日发生在北京地区的一次强冰雹天气过程进行了数值模拟研究,并与观测的雷达回波、冰雹云移动路径和冰雹落区进行比较,在此基础上探讨了城市和农田两种下垫面对雹云的影响。结果表明,由于"城市热岛"效应的作用,城市下垫面的地面感热通量显著增加,有利于雹云的发展增强和大冰雹的形成,使地面累积降雹量增加,但对雹云移动路径影响不大。农田下垫面具有较大的潜热通量,局地蒸发强,有利于大量小冰雹的形成,云中冰雹含量增加,但降雹强度较弱,地面累积降雹量小。

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.