Horizontal Vortex Tubes near a Simulated Tornado: Three-Dimensional Structure and Kinematics

Abstract

Supercell thunderstorms can produce a wide spectrum of vortical structures, ranging from midlevel mesocyclones to small-scale suction vortices within tornadoes. A less documented class of vortices are horizontally-oriented vortex tubes near and/or wrapping about tornadoes, that are observed either visually or in high-resolution Doppler radar data. In this study, an idealized numerical simulation of a tornadic supercell at 100 m grid spacing is used to analyze the three-dimensional (3D) structure and kinematics of horizontal vortices (HVs) that interact with a simulated tornado. Visualizations based on direct volume rendering aided by visual observations of HVs in a real tornado reveal the existence of a complex distribution of 3D vortex tubes surrounding the tornadic flow throughout the simulation. A distinct class of HVs originates in two key regions at the surface: around the base of the tornado and in the rear-flank downdraft (RFD) outflow and are believed to have been generated via surface friction in regions of strong horizontal near-surface wind. HVs around the tornado are produced in the tornado outer circulation and rise abruptly in its periphery, assuming a variety of complex shapes, while HVs to the south-southeast of the tornado, within the RFD outflow, ascend gradually in the updraft.

An Analysis of an Ostensible Anticyclonic Tornado from 9 May 2016 Using High-Resolution, Rapid-Scan Radar Data

“…Though the authors are not aware of radar observations of quasi-horizontal vortices (be they actually horizontal, slightly tilted, or arched) in the literature similar to those seen on 9 May 2016 in the forward-flank echo of a supercell, there are observations of quasi-horizontal vortices elsewhere in supercells. For example, quasihorizontal vortices have been seen in high-resolution simulations (e.g., Orf et al 2017;Oliveira et al 2019) and observations from mobile radars (e.g., Wurman and Kosiba 2013;Houser et al 2016) to the south of strong tornadoes, perhaps associated with internal rear-flank downdraft surges and/or near-ground frictional effects. However, these quasi-horizontal vortices are generally smaller in size and occur in a distinctly different part of the storm compared to the two examined in this paper.…”