Mobile, X-band, Polarimetric Doppler Radar Observations of the 4 May 2007 Greensburg, Kansas, Tornadic Supercell

Abstract

On 4 May 2007, a supercell produced an EF-5 tornado that severely damaged the town of Greensburg, Kansas. Volumetric data were collected in the ''Greensburg storm'' by the University of Massachusetts X-band, mobile, polarimetric Doppler radar (UMass X-Pol) for 70 min; 10 tornadoes were detected. This mobile Doppler radar dataset is one of only a few documenting an EF-5 tornado and the supercell's transition from short-track, cyclic tornado production (mode 1) to long-track tornado production (mode 2). Using bootstrap confidence intervals, it is determined that the mode-2 tornadoes moved in the same direction as the supercell vault. In contrast, the mode-1 tornadoes moved to the left with respect to the vault.From polarimetric data collected in this storm, the authors infer the presence of large, oblate drops (high Z DR , high r hv ) in the forward flank and surrounding some of the tornadoes. The authors speculate that the weak-echo column (WEC) in the Greensburg tornado, which extended above 10 km AGL, was caused primarily by the centrifuging of hydrometeors at low levels and rapid upward transport of relatively scattererfree air at upper levels. This WEC was collocated at low levels with a low-Z DR , low-r hv column, indicating lofted debris.Dual-Doppler analyses, generated at ;10-min intervals using data from UMass X-Pol and the Dodge City, Kansas, Weather Surveillance Radar-1988 Doppler (WSR-88D), were used to locate updrafts and downdrafts near the hook echo. In the immediate vicinity of tornadoes, diminished Z DR values downstream of analyzed downdrafts may indicate the ingestion by tornadoes of relatively small drops, fallout of larger drops, or a combination of both.

Bulk Hook Echo Raindrop Sizes Retrieved Using Mobile, Polarimetric Doppler Radar Observations

“…The small number of hook echo cases used in the study and the need for data from high-resolution dual-polarization radars was emphasized. In addition, Tanamachi et al (2012) used data from an X-band, polarimetric mobile Doppler radar developed at the University of Massachusetts (UMass X-Pol; Bluestein et al 2007) to infer small drops around several weak tornadoes and near dual-Doppler-analyzed downdrafts in the Greensburg, Kansas, supercell, providing possible evidence of mechanism 2. Several additional recent studies have investigated supercells by using polarimetric radar data from fixed or mobile radars, but the focus of such studies was not on hook echo DSDs (e.g., Ryzhkov et al 2005b;Bluestein et al 2007;Romine et al 2008;Kumjian and Ryzhkov 2008b;Kumjian et al 2010;Snyder et al 2013).…”

Rapid Volumetric Growth of Misocyclone and Vault-Like Structure in Horizontal Shear Observed by Phased Array Weather Radar

“…We note that the maximum height and lateral scale of the vault-like structure estimated at 40-dBZ isosurface were 1.3 km and 2−3 km, respectively. The obtained spatial scale is small compared with those found in typical supercells (e.g., Tanamachi et al 2012).…”

“…Figure 2 shows a temporal change of reflectivity structure observed by PAWR. In the top panels, a vault-like structure (thick yellow arrows), which is a low reflectivity region that extends to higher altitudes and forms a rounded ceiling (e.g., Browning and Donaldson 1963;Tanamachi et al 2012), appeared at ~0758 JST and rapidly developed to the maximum spatial scale at 0802− 0803 JST. In the horizontal cross sections at 0.6 km ASL, the vault-like structure is recognized as a kink.…”

A Mobile Rapid-Scanning X-band Polarimetric (RaXPol) Doppler Radar System

“…5). At higher elevation angles, a weak-echo hole (e.g., Fujita 1981;Wakimoto and Martner 1992;Wurman et al 1996;Bluestein et al 2003Bluestein et al , 2004Bluestein et al , 2007bWakimoto et al 2011;Palmer et al 2011;Tanamachi et al 2012) is evident (Fig. 6).…”

“…Mobile, polarimetric Doppler radars operating at X band have been used for the same purposes (e.g., Bluestein et al 2007a;Tanamachi et al 2012;Snyder et al 2010Snyder et al , 2013Wurman et al 2012), but, again, these radars are not rapid-scan radars.…”