Generation Mechanism, Structure and Dynamics of Violent Vortices in the Atmospheric Boundary layer and their Roles in Turbulent Transport

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Generation mechanisms, structures and dynamics of dust devils, steam devils and tornadoes are studied. Dust devils are formed when circulation about the vertical axis, which is generated at mid-levels in a convective mixed layer, is transported by downdrafts toward low-levels, and then to updraft regions while nearly conserving the angular momentum. Steam devils in a moist convective mixed layer without precipitation develop in a similar way to dust devils. Those with precipitation, however, are caused by collisions of boundaries of cold pools from precipitating area. Radial distribution of tangential velocity in these strong vortices is found to have two different regimes which are dominated by the dynamics of a rotating boundary layer.