How Environmental Streamwise Vorticity Modulates the Streamwise Vorticity Current

It has been established that streamwise vorticity is important for the creation and maintenance of right-moving supercells. Storm-Relative Helicity (SRH), a measure of the environmental streamwise vorticity available to a right-moving supercell, is a key focal point in forecasting the strength of supercells. Larger amounts of SRH are generally linked to stronger low- and mid-level vertical vorticity.

Some recent studies (Orf et al. (2017); Schueth and Weiss (2019)) have shown that a coherent localized ribbon of strong streamwise vorticity feeds the supercell updraft and originates from the forward flank. This feature is called the streamwise vorticity current (SVC). The SVC is collocated with the forward flank baroclinic boundary, and it is hypothesized that the vorticity originates baroclinically. Further simulations and analysis have shown that parcels with pre-existing environmental streamwise vorticity follow favorable parcel paths to acquire baroclinic vorticity, all the while being stretched in the horizontal before being tilted into the updraft. The streamwise vorticity magnitude in the SVC increases as parcels approach the updraft, deepening the pressure perturbation, and accelerating upstream parcels in a feedback process.

The SVC is not found in all supercell observations or simulations. Thus, certain environmental factors likely play a role in the genesis, maintenance, and magnitude of the SVC. In this project, the sensitivity of the SVC magnitude is compared to the SRH available in the environment, accomplished by systematically adjusting the hodograph curvature across multiple simulations, increasing or decreasing the SRH. Baroclinic and barotropic forcing for the SVC will be discussed in the context of this suite of simulations.

During the TORUS (Targeted Observation by Radars and UAS of Supercells) project in 2019, 19 supercells were sampled, some of which had SVCs, and some which did not. A preliminary comparison between the environments of these cases, particularly hodographs, and SVCs will be provided to validate the simulation results.