SELF-SUSTAINING INTENSE VORTICES

We seek to identify an accessible observable for anticipating tornadog enesis in mesocyclones, because such tornadoes are characterized by ex ceptionally extended lifespan, exceptionally long and wide path, and e xceptionally high wind speed. We associate tornadogenesis with the tra nsition from a one-cell vortex to a two-cell vortex. After such a tran sition, the core (''eye'') of the vortex consists of virtually nonrota ting, slowly recirculating, relatively dry air. Rapidly swirling air s wiftly ascends in an annulus (''eyewall''), situated at a small but fi nite distance from the axis of rotation. The swiftly ascending air is described by a locus of thermodynamic states well approximated by a mo ist adiabat. Such a transition from a one-cell vortex to a two-cell vo rtex, on vastly larger lateral scale, is known to characterize the int ensification of a tropical storm to a typhoon. We adopt a simplified, tractable model for our initial analytic efforts. We examine a quasist eady axisymmetric vortex with a four-part structure, consisting of a b ulk potential vortex, a near-ground inflow layer, an ''eyewall'', and an ''eye''. We inquire under what conditions such a four-part intense vortex, formed in convectively unstable stratified air, is self-sustai ning. In particular, we inquire whether the vertical profile of the an gular momentum outside of the eyewall is a discriminant for identifyin g the conditions for which an intense (two-cell) vortex could be self- sustaining. Guidance from laboratory experiments would be helpful conc erning the turnaround (the portion of the flow field in which the near -ground swirling inflow separates to form the swirling updraft of the eyewall annulus).