A New Pathway for Tornadogenesis Exposed By Numerical Simulations of Supercells in Turbulent Environments

This presentation will summarize and discuss the key findings from a recent numerical modeling study (Markowski 2024, Journal of the Atmospheric Sciences), which examined tornadogenesis in a supercell simulation incorporating a turbulent environmental boundary layer.  The simulation configuration represents a departure from the set-up used in almost all prior simulations, in that past simulations almost always have had a laminar environmental boundary layer. Substantial near-surface vertical vorticity (ζ > 0.03 s⁻¹ at z = 7.5 m) is present in the form of elongated streaks oriented with the southerly ground-relative winds. These ζ streaks coincide with undulations in predominantly horizontal, westward-directed environmental vortex lines, shaped by vertical motions linked to coherent turbulent structures—features long recognized in the boundary layer and turbulence literature. The ζ streaks act as preferred sites for tornadogenesis, and may even facilitate it, as environmental ζ can be quickly intensified by the strong convergence beneath supercell updrafts. Interestingly, the simulation lacks evidence of the traditional "baroclinic mechanism" of tornadogenesis, despite the supercell's structure and evolution closely resembling that seen in cases in which the baroclinic mechanism is operating.  I will try to make sense of what all of these findings might mean.  The presentation also will highlight unexpected differences in cold pool behavior between storms initialized with turbulent versus laminar boundary layers.