The Structure of Tornadoes near Attica, Kansas, on 12 May 2004: High-Resolution, Mobile, Doppler Radar Observations

摘要

The University of Massachusetts W- and X-band, mobile, Doppler radars scanned several tornadoes at close range in south-central Kansas on 12 May 2004. The detailed vertical structure of the Doppler wind and radar reflectivity fields of one of the tornadoes is described with the aid of boresighted video. The inside wall of a weak-echo hole inside the tornado was terminated at the bottom as a bowl-shaped boundary within several tens of meters of the ground. Doppler signatures of horizontal vortices were noted along one edge in the lowest 500 m of the tornado. The vertical structure of Doppler velocity displayed significant variations on the 100-m scale. Near the center of the tornado, a quasi-horizontal, radial bulge of the weak-echo hole at ～500-600 m AGL dropped to about 400 m above the ground and was evident as a weak-echo band to the south of the tornado. It is suggested that this feature represents echo-weak material transported radially outward by a vertical circulation. Significant vertical variations of Doppler velocity were found in the surface friction layer both inside and outside the tornado core. The shape of a weak-echo notch that was associated with a hook echo wrapped around the tornado is described. Highest Doppler velocities were located outside the condensation funnel. The structure of the other tornadoes is also described, but with much less detail. Some of the analyses are compared with numerical simulations of tornado-like vortices done elsewhere.