The Developing Structure of a Black Storm and Its Numerical Experiment of Different Model Resolution

The developing structure and evolution of a black storm occurred in the northwest region of China from 4 to 6 May 1993 (“93.5”) can be basically simulated by using a control experiment of the improved MM4 model with high resolution PBL parameterization and 40 km fine-mesh. The simulated results show that the black storm was associated with both a mesoscale cyclonic strong vortex in the PBL and a vertical vortex column in the troposphere during the developing stage. The lower (upper) part of this vortex column, stretching to the tropopause was cyclonic (anticyclonic) vortex column associated with intensive converence (divergence) inflow (outflow). According to the cross section of the equivatlent potential temperature, the major differences of the structure of the black storm from that of black storm from of general front are: the steep slope of the boundary surfaces, the large horizontal gradient of θe, the quite intensive baroclinity, the obvious warm-core in the PBL. The warm-cored structure in the lower part of the black storm was related to intensive thermal over underlying surface. The comparison experiments of the different PBL parameterization and model spatial resolutions show that it would be necessary to enhance the spatial resolution of the mesoscale numerical model and to adopt a better PBL parameterized scheme in order to improve the simulation of the developing structure and evolution of black storm.