Numerical Experiments of a Convective Cloud with a High Cloud Base in Shear Flows

[摘要] A numerical model including dynamical and cloud physical processes is formulated to simulate the observational evidences, concerning the severe storms frequently observed in the North American Continent. Our concerns are restricted to five points; (1) generation of a cold dome and a convergence line at the surface, (2) upshear tilting of an updraft, (3) a long-lasting nature, (4) a right-moving convective cloud and (5) generation of vertical vdrticity. To examine roles of vertical wind profiles on the above-mentioned features, we make numerical calculation for four cases with different wind profiles.It is shown that the point (1) can be explained by cooling due to evaporation of raindrops falling in the subcloud layer. In the case for which the direction of the basic wind shear turns with height, a long-lasting nature of the convective cloud, upshear tilting of an updraft and the small deviation of the rain region movement from the environmental wind direction are obtained. The jet type wind plays an important role in (3), because it transports raindrops not to cut off the supply of fresh air from the subcloud layer into the updraft region. Vertical vorticity is created mainly by the tilting term at the developing stage and then the vertical advection and the divergence term as well as the tilting term are principal terms. A pair of strong anticyclonic and weak cyclonic vortices are found in the rain region.

[学科分类] 大气科学