Conditions for Two-Cell Structure in Severe Vortical Storms

摘要

Predictive capability for the intensity of severe vortical storms of the troposphere entails anticipation of which systems will undergo transition from one-cell to two-cell structure, and which will not. Roughly half of all tropical storms, and nearly half of all mesocyclones, undergo this transition, in which the low-level pressure differential between periphery and center may increase from 0(1%) to 0(10%) of atmospheric pressure, and the peak swirl speed may increase from 0(50 m/s) to 0(100 m/s). The transition entails insertion of relatively dry, nonrotating, compressionally heated, tropopause-level air at the axis of the vortex, such that slowly recirculating air (an eye) displaces to an annulus (the eyewall) the rapidly swirling cloudy updraft arising from separation of the low-level inflow layer. This investigation inquires whether the vertical stratification of the circulation at the periphery of the vortex (which varies only slowly in time) might not provide a relatively accessible observable that suggests whether two-cell structure can be sustained by the vortex.