88th Annual Meeting (20-24 January 2008)

Wednesday, 23 January 2008
Close-range observations of a tornadic supercell with C-band polarimetric Doppler radar
Exhibit Hall B (Ernest N. Morial Convention Center)
Matthew R. Kumjian, CIMMS/Univ. of Oklahoma and NOAA/NSSL, Norman, OK; and A. V. Ryzhkov, J. L. Alford, M. Knight, and J. W. Conway
Poster PDF (1.6 MB)
On March 1, 2007, a supercell thunderstorm produced a devastating EF-4 tornado in Enterprise, Alabama. Nine people were killed, eight of which were students that died when their high school suffered a direct hit from the tornado. Amidst the tragic events of the day, the Enterprise Electronics Corporation Sidpol polarimetric radar, also located in Enterprise, collected the first known data set of a violent tornadic storm at extremely close range (within 5 km) at C band. The data was collected starting about 45 minutes before the tornado formed until about 30 minutes after the tornado passed through Enterprise. This unique data set contains striking high resolution polarimetric features at low-levels of the storm which are analyzed in detail to provide remarkable insight into convective storm microphysics. The signatures presented include the tornadic debris signature (TDS), the ZDR arc, and the midlevel rings of ZDR and ρHV. From the microphysics interpretations of these signatures, aspects of storm behavior and morphology can be inferred.

Measurements at C band require some special considerations. The smaller wavelength causes large raindrops and small hailstones to behave as resonant scatterers. Thus, significant attenuation and differential attenuation may occur. Additionally, when strong precipitation cores pass over the radar (a consequence of such close-range observations), the attenuation and differential attenuation are augmented. Without proper correction for such attenuation, a correct interpretation of the data is nearly impossible. We present a robust correction procedure that was recently developed and validated at NSSL. This procedure accounts for intense precipitation cores that, although small in spatial extent, may cause a significant proportion of the observed attenuation. These considerations and the correction procedure should be of special interest to broadcast meteorologists, whose television station radars are often C band, as well as others who will use short wavelength polarimetric radar data operationally in environments of convective storms.

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