Dual-polarization observations of tornadoes at close range made with a mobile X-band Doppler radar

Data were collected at close range (~ 4 – 14 km) in several tornadoes using a mobile (truck mounted), dual-polarization, X-band, Doppler radar on 12 and 29 May 2004 in Kansas and Oklahoma, respectively; photographs taken at the radar were used to estimate the size of the debris clouds, funnel clouds, etc., when visible, and were compared with the radar-observed features. It is believed that some of these dual-pol datasets are the first collected with simultaneous visual documentation at close range. The radar, which has a 1.25 deg half-power beamwidth, was designed and built at the University of Massachusetts in Amherst and operated by students from the University of Oklahoma. In the 12 May tornadoes, a visible circular debris ring of low values of ZDR was sometimes easily distinguished from surrounding spiral bands of precipitation of much higher values of ZDR. In the 29 May tornadoes, which were hidden from our view behind a curtain of precipitation, the vortex and weak-echo hole were at times relatively wide and had small-scale multiple vortices embedded within them; however, a debris ring was not evident in the ZDR field. When the tornado had multiple vortices, a band of relatively high ZDR, indicative of rain, was evident feeding into the tornado between two of its sub-vortices.