3D GBVTD analysis of the Spencer, South Dakota (1998) Tornado

Several 3D GBVTD analyses have been conducted using volumetric data in the tornado that approached and crossed Spencer, South Dakota in 1998, destroying much of the town and killing 6 people. The GBVTD analyses resolve a two-cell tornado structure, with the strongest winds at the lowest levels. Core radius is relatively constant with height except very near the ground, and multiple scales of motion are revealed in some volumes. Swirl ratio, central pressure deficit, convergence and other tornado structural parameters are calculated and compared to those analyzed using traditional techniques and compared to those analyzed in the Mulhall tornado.