Mobile Observations of Near-Surface Vorticity Features North of the Supercell Updraft

Recent high-resolution numerical simulations have revealed the existence of concentrated streamwise vorticity at the surface, or “vorticity rivers”, which appear in the main precipitation region of supercells. These rivers are believed to play a role in the near-ground rotation of tornadic storms, but their existence in real-world data observations has yet to be shown. As such, the Rivers of Vorticity in Supercells (RiVorS) field project aimed to identify these structures, if they exist, to examine their kinematic and thermodynamic properties. Several measurement platforms were used during RiVorS, including mobile mesonets with sounding capability, unmanned aerial aircraft, a surface-based profiling system, and mobile Doppler radars.

The project ran May-June 2017 and collected data on several supercells including a few tornadic. During operation concentrated, high-resolution mobile mesonet observations were collected immediately north of any present low-level mesoscyclone. In this region, several small-scale baroclinic regions on the order of 100-m wide with temperature perturbations approaching +10°C were observed. These baroclinic zones were short lived and were typically accompanied by a sharp visual change in the drop size distribution. Kinematic and thermodynamics surface observations will be compared with mobile radar to determine if these features are identifiable in remote data, where they originate from, and what potential role they play in near-ground rotation.