Abstract
Single-Doppler Velocity data reveal that a dominant feature in the Union City, Okla., tornadic thunderstorm is a core mesocyclonic circulation, 2–6 km in diameter, extending to at least 9 km above ground. There is an apparent flow through the precipitation echo at low levels and divergence at high levels. Considerable similarity appears between mid-level flow structure around the mesocyclone core and that observed around a solid rotating cyclinder embedded in classical potential flow. As tornado time approaches, core circulation tangential velocities increase while diameter decreases. Simultaneously, the collapse of storm top and extensive echo overhang suggest updraft weakening.
