Among the numerous hypotheses for the primary source of rotation in small-scale vortices, we are concentrating most strongly on two. First, that the source of rotation may arise from the interaction of convection with a mean horizontal or vertical shear zone. This mechanism of vortex formation is dynamically similar to that proposed by Wakimoto and Wilson, Brady and Szoke, Lee and Wilhelmson, and others, for non-supercell tornadoes, gustnadoes, and landspouts. The second hypothesis we are exploring emerged from laboratory (Willis and Deardorff ) and numerical simulations (Cortege and Balachandar, Shapiro and Kogan). These studies simulated vortex formation in the absence of any imposed mean wind shears. In these cases, angular momentum may be produced by local processes associated with larger scale convective circulations themselves.
The energetics associated with the maintenance of such vortices is also examined. In particular, are continuous sources of potential energy and vorticity required? Furthermore, it is hypothesized that rotating elements in the boundary layer may transport more heat and momentum than nonrotating convective elements and thus, may play a role in the favored location of deep convective initiation.
Increased knowledge of dry microscale flows should contribute to the understanding of some of the critical processes for tornadogenesis, as well to those for other microscale vortical flows, e.g., fire whirls. However, these flow are of interest in their own right. Fujita and Horn have reported that dust devils can become quite intense, exhibit multiple vortex structure, and cause damage and fatalities. Hess and Spillane point out that dust devils can pose severe hazards to small aircraft. Lastly, the results of this study may add insight to the processes responsible for the formation of low-level rotation in tornadoes. The processes associated with the interaction of the vortex with the surface may be important to tornadogenesis, maintenance and demise.