A Finescale Radar Examination of the Tornadic Debris Signature and Weak-Echo Reflectivity Band Associated with a Large, Violent Tornado

Abstract

AbstractHigh-resolution data of the tornadic debris signature (TDS) and weak-echo reflectivity band (WRB) associated with a large, violent tornado on 24 May 2011 in central Oklahoma are examined using a rapid-scan, X-band, polarimetric, mobile Doppler radar. Various characteristics of these features and their evolution are examined over time intervals of 20 s or less. The formation of the TDS, debris fallout, and inhomogeneities in the TDS structure, are analyzed from volumetric and single-elevation observations. Constant-radius vertical cross sections of Doppler velocity, reflectivity, and copolar cross-correlation coefficient are compared at various times during the tornado’s life cycle; from them it is found that the weak echo column (WEC) is considerably narrower than the TDS and the WEC is confined to the strong gradient of Doppler velocities in the tornado’s core. The TDS of the mature tornado extends radially outward, bound approximately by the 40 m s−1 radial isodop.Rapid-scan, near-surface data were collected for a period of 6 min, during which 2-s single-elevation PPI updates at 1° were available at heights below 100 m above radar level. During this period, a WRB associated with a visually observed horizontal vortex developed east of the tornado, along the leading edge of the secondary rear-flank gust front, as the tornado was rapidly intensifying. A relationship was noted between reduced radar-observed reflectivity and increased radar-observed radial convergence/divergence in the vicinity of the horizontal vortex as it strengthened. This feature is qualitatively analyzed and hypotheses explaining its generation and structure are discussed.