Vorticity Evolution Leading to Tornadogenesis and Tornadogenesis Failure in Simulated Supercells

Abstract

A three-dimensional idealized cloud model was used to study the storm-scale differences between simulated supercells that produce tornado-like vortices and those that do not. Each simulation was initialized with a different Rapid Update Cycle, version 2 (RUC-2), sounding that was associated with tornadic and nontornadic supercells in nature. The focus is an analysis of vorticity along backward-integrated trajectories leading up to tornadogenesis (19 simulations) and tornadogenesis failure (14 simulations). In so doing, the differences between the nontornadic and tornadic cases can be explored in relation to their associated environmental sounding.Backward-integrated trajectories seeded in the near-surface circulation indicate that the largest differences in vertical vorticity production between the tornadic and nontornadic simulations occur in parcels that descend to the surface from aloft (i.e., descending). Thus, the results from this study support the hypothesis that descending air in the rear of the storm is crucial to tornadogenesis. In the tornadic simulations, the descending parcels experience more negative vertical vorticity production during descent and larger tilting of horizontal vorticity into positive vertical vorticity after reaching the surface, owing to stronger horizontal gradients of vertical velocity. The larger vertical velocities experienced by the trajectories just prior to tornadogenesis in the tornadic simulations are associated with environmental soundings of larger CAPE, smaller convective inhibition (CIN), and larger 0-1-km storm-relative environmental helicity. Furthermore, in contrast with what might be expected from previous works, trajectories entering the incipient tornadic circulations are more negatively buoyant than those entering the nontornadic circulations.

Applications of Vortex Gas Models to Tornadogenesis and Maintenance

“…It is generally accepted that the process of tornadogenesis involves vortices generated baroclinically by the rear flank downdraft that are then turned into the vertical (see, e.g., Naylor and Gilmore [2013], Markowski et al [2014]) and then potentially anchored at the surface. Recent numerical simulations of Orf et al [2014Orf et al [ , 2016 indicate two potentially important factors contributing to tornadogenesis: (a) consolidation of vertical vortices generated along the forward flank downdraft boundary and anchored at the surface that enter and strengthen the developing tornado; and (b) a streamwise current of horizontally generated vorticity that is tilted upward into the low-level mesocyclone.…”

Simulating the 20 May 2013 Moore, Oklahoma tornado with a 100‐metre grid‐length NWP model

“…Downdrafts (rather than updrafts) are considered important in generating near‐surface vertical vorticity by transporting vertical vorticity from mid‐levels to the surface (e.g. Rotunno and Klemp, ; Markowski and Richardson, ; Kosiba et al , ; Dahl et al , ; Markowski and Richardson, ; Naylor and Gilmore, ). Due to the deep‐layer wind shear and upper‐level winds, the bulk of the hydrometeors in a supercell is deposited on the forward flank of the main updraft.…”

Genesis, Maintenance and Demise of a Simulated Tornado and the Evolution of Its Preceding Descending Reflectivity Core (DRC)

“…The model took 27 min to form the supercell from the initial warm bubble. The formation of a supercell was defined as the earliest time when the 2-5-km integrated updraft helicity reached 900 m 2 s −2 , as introduced by Naylor and Gilmore [6]. After meeting the supercell criteria, the value of 2- The above analyses showed that the cloud model simulated the supercell and tornado reasonably well by using a real radiosonde background.…”

“…However, the whole life cycle of a tornado from genesis to maintenance and demise, most notably in terms of the near-surface features, is hard to capture with observational data [3,4]. Relative to observations, numerical modeling can provide more thermodynamic information close to the tornado scale with higher spatial and temporal resolutions [5,6].…”

“…So far, only few studies have documented NWP-model simulations of real-world tornadoes at tornado-resolving resolutions [8][9][10][11]. A common practice in tornado modeling is to use an idealized cloud model, where the parent storm is typically initiated with a warm bubble in a uniform background based on a radiosonde profile (e.g., [6,12,13]).…”