8A.8
The "Owl Horn" radar signature in developing Southern-Plains thunderstorms
Matthew R. Kramar, University of Oklahoma, Norman, OK; and H. B. Bluestein, A. L. Pazmany, and J. D. Tuttle
Using a mobile X-band Doppler radar system built by a group at the University of Massachusetts at Amherst, we have been able to survey supercell thunderstorms with a much finer spatial and temporal resolution than the WSR-88D radar offers, since the WSR-88D radars are confined to fixed sites, while we can consistently approach storms at ranges of only 10 to 20 km. Consequently we are able to see features of supercell thunderstorms that might otherwise go unresolved by stationary observing systems. In the course of the 2001 severe storm season in the Southern Plains, we observed a curious, recurring reflectivity signature on our radar display that we have called the "Owl Horn" signature (because the radar reflectivity signature resembles the ears of an owl). The feature was apparent from various viewing angles with respect to the storms exhibiting the signature, thus eliminating the possibility that it was an artifact of the radar. The U. Mass. radar operated with an antenna beamwidth of 1.25 degrees, transmitted 1 microsecond pulses, and had a range resolution of 150m.
We have undertaken a study of the "Owl Horn" signature using the Tracking Radar Echoes by Correlation technique (TREC). While TREC has previously been applied to clear air and hurricane environments (Tuttle and Foote, 1990; Tuttle and Gall, 1999), absent from the literature is an application of TREC to severe storms and supercell storms in the interest of studying supercell evolution, although Rinehart (1979) has previously studied internal storm motions by applying TREC to severe storms. Through the application of TREC to our radar reflectivity data (Doppler wind data were not available in 2001) during May and June, 2001, we computed an estimate of the horizontal wind field around and in the "Owl Horn" signature. TREC revealed the presence of a wind shift line, coincident with the signature in the reflectivity.
Recently, we have found evidence of the “Owl Horn” signature in numerical model simulations as well, which has enabled us to examine both the simulated ambient atmospheric parameters during the signature’s presence, as well as the sensitivity of the “Owl Horn” to changes in those parameters, primarily the environmental wind shear. In this paper we present results of our TREC analysis and model simulations, and speculate as to the conditions in which the “Owl Horn” echo forms.
Session 8A, Severe Weather II
Sunday, 10 August 2003, 10:30 AM-12:30 PM
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