Dual-Doppler and Single-Doppler Analysis of a Tornadic Storm Undergoing Mergers and Repeated Tornadogenesis

Abstract

Dual-Doppler observations with unprecedented finescale spatial and temporal resolution are used to characterize the vector wind field in and near a tornado occurring near Kiefer, Oklahoma, on 26 May 1997. Analyses of the dual-Doppler vector wind fields document in detail, for the first time, several structures associated with the tornado: a proximate updraft region, a rear-flank downdraft wrapping around the tornado, a double gust front structure occluding near the tornado, and a region of enhanced vorticity separated from the tornado that may have been associated with cyclic tornadogenesis. The analyses are compared to conceptual and computer models of tornadic storms. A subsequent tornadogenesis was observed with radar every 18 s, providing a finescale temporal view of the genesis process. The genesis process was complex and the evolution of tornado intensity parameters was not monotonic in time. Low-level rotation contracted and intensified, then broadened, then contracted and intensified a second time to form the tornado. The initial tornadogenesis was coincident with the merger of the main supercell and a much smaller convective storm. This tornado, which was always surrounded by substantial precipitation originating from both storms, began to dissipate just a few minutes after genesis, and the rotation both aloft and near the surface weakened substantially. A second storm merger, with a much larger and supercellular storm, was coincident with a reintensification of the mesocyclone aloft, a new hook echo development, and the genesis of a short-lived tornado. After the dissipation of this second tornado, the merger disrupted the structure of the supercell storm, the hook echo was absorbed, and the mesocyclone dissipated. The current analysis suggests a process in which storm mergers may, in sequence, aid tornadogenesis by enhancing surface convergence, or through another mechanism, but subsequently disrupt the tornado?s parent supercell perhaps by cooling the inflow air, with the result being short-lived tornadoes.