The Effects of Surface Drag on the Near-Storm Environment, Storm Structure and Sources of Vertical Vorticity in Idealized Supercell Simulations

Abstract

Recent tornadogensis literature has been in broad agreement that baroclinic generation of horizontal vorticity is critical for producing low-level rotation that precedes the development of a tornado in a supercell. However, it has also been suggested that frictional generation of vorticity can be the dominant source of vorticity for the incipient tornado (e.g. Roberts and Zue 2016). Studies agree that air parcels gaining the most significant vertical vorticity near the surface tend to originate in the forward flank of the storm and descend toward the rear of the storm before turning sharply upwards. In an effort to further understand sources of near-surface vertical vorticity in tornadic storms, idealized supercell simulations with and without surface drag are investigated alongside additional simulations where surface drag is turned on some time into the model integration and modifications to the environmental sounding are made. A forward-integration trajectory scheme will be employed to calculate a vorticity budget along air parcel trajectories that attain tornadic strength vertical vorticity near the surface. It is hypothesized that sources of vertical vorticity ingested by a tornadic vortex varies depending on the near-storm environment. The role of surface drag as a source of vorticity and its effect on the sounding in idealized supercell environments will be presented.