TY - JOUR
T1 - Comparing observations and simulations of the streamwise vorticity current and the forward flank convergence boundary in a supercell storm
AU - Schueth, Alexander
AU - Weiss, Christopher
AU - Dahl, Johannes
N1 - Funding Information:
Acknowledgments. We thank George Bryan for providing and maintaining the CM1, and the open-source community for providing the Py-ART (Helmus and Collis 2016) and MetPy (May et al. 2008–2020) Python packages used in this analysis. We also thank Erik Rasmussen and Sean Waugh for the observed sounding from the RiVorS project. We acknowledge Eric Bruning for providing helpful insight as a member for the first author’s M.S thesis committee. The supercell simulation was performed at the Texas Tech University High Performance Computing Center (HPCC). Schueth and Weiss are supported by NSF Grants IIS-1527183 and AGS-1824713, and Dahl is supported by AGS-1651786. Finally, we are very grateful for insightful discussions with Kelton Halbert, Jannick Fischer, and Cameron Nixon and the helpful comments provided by Leigh Orf as well as the two anonymous reviewers that improved the quality of this paper.
Publisher Copyright:
© 2021 American Meteorological Society. All rights reserved.
PY - 2021/6
Y1 - 2021/6
N2 - The forward-flank convergence boundary (FFCB) in supercells has been well documented in many observational and modeling studies. It is theorized that the FFCB is a focal point for the baroclinic generation of vorticity. This vorticity is generally horizontal and streamwise in nature, which can then be tilted and converted to midlevel (3 6 km AGL) vertical vorticity. Previous modeling studies of supercells often show horizontal streamwise vorticity present behind the FFCB, with higher-resolution simulations resolving larger magnitudes of horizontal vorticity. Recently, studies have shown a particularly strong realization of this vorticity called the streamwise vorticity current (SVC). In this study, a tornadic supercell is simulated with the Bryan Cloud Model at 125-m horizontal grid spacing, and a coherent SVC is shown to be present. Simulated range height indicator (RHI) data show the strongest horizontal vorticity is located on the periphery of a steady-state Kelvin Helmholtz billow in the FFCB head. Additionally, a similar structure is found in two separate observed cases with the Texas Tech University Ka-band (TTUKa)mobile radar RHIs.Analyzing vorticity budgets for parcels in the vicinity of the FFCB head in the simulation, stretching of vorticity is the primary contributor to the strong streamwise vorticity, while baroclinic generation of vorticity plays a smaller role.
AB - The forward-flank convergence boundary (FFCB) in supercells has been well documented in many observational and modeling studies. It is theorized that the FFCB is a focal point for the baroclinic generation of vorticity. This vorticity is generally horizontal and streamwise in nature, which can then be tilted and converted to midlevel (3 6 km AGL) vertical vorticity. Previous modeling studies of supercells often show horizontal streamwise vorticity present behind the FFCB, with higher-resolution simulations resolving larger magnitudes of horizontal vorticity. Recently, studies have shown a particularly strong realization of this vorticity called the streamwise vorticity current (SVC). In this study, a tornadic supercell is simulated with the Bryan Cloud Model at 125-m horizontal grid spacing, and a coherent SVC is shown to be present. Simulated range height indicator (RHI) data show the strongest horizontal vorticity is located on the periphery of a steady-state Kelvin Helmholtz billow in the FFCB head. Additionally, a similar structure is found in two separate observed cases with the Texas Tech University Ka-band (TTUKa)mobile radar RHIs.Analyzing vorticity budgets for parcels in the vicinity of the FFCB head in the simulation, stretching of vorticity is the primary contributor to the strong streamwise vorticity, while baroclinic generation of vorticity plays a smaller role.
KW - Cold pools
KW - Density currents
KW - Kelvin-Helmholtz instabilities
KW - Radars/Radar observations
KW - Supercells
KW - Vorticity
UR - http://www.scopus.com/inward/record.url?scp=85109007436&partnerID=8YFLogxK
U2 - 10.1175/MWR-D-20-0251.1
DO - 10.1175/MWR-D-20-0251.1
M3 - Article
VL - 149
SP - 1651
EP - 1671
JO - Monthly Weather Review
JF - Monthly Weather Review
IS - 6
ER -