Sunday, 22 January 2012
Observations of a Supercell and Weak Tornado Made with a Rapid-Scan, Polarimetric, Mobile Radar
Hall E (New Orleans Convention Center )
A rapid-scan, X-band, polarimetric, mobile Doppler radar is used to collect horizontal reflectivity, differential reflectivity, cross correlation coefficient and radial velocity data of a supercell that produced two EF-0 tornadoes in Osage County, OK on 18 June 2011. Volume scans of the first tornado, which lasted a few minutes, were acquired every 30 s. Analysis of data reveals several common polarimetric radar signatures associated with supercells including the low-level inflow, low-level hail and differential reflectivity arc signatures. The low-level inflow and differential reflectivity arc signatures both decreased in prominence around the time of tornado dissipation. No tornadic debris signature was noted, likely owing to the fact that the tornado was too weak to loft heavy debris, suggesting it is difficult for polarimetric radars to detect weak tornadoes. A Three Body Scatter Spike was also evident in the data, suggesting the presence of large hail aloft. Doppler velocity data reveal that mid-level mesocyclone intensification is not a pre-requisite for tornadogenesis. A trend of increasing azimuthal shear with time up to tornado dissipation is observed in the lowest two elevation scans, as well as within the low and midlevel mesocyclones. Azimuthal shear decreased after tornado dissipation in the lowest two scans and the low-level mesocyclone, but not with the midlevel mesocyclone. Furthermore, an anticyclonic circulation accompanied the cyclonic mesocyclone. A hook signature in the reflectivity field was observed with the mesoanticyclone, which later morphed into a linear feature.
Supplementary URL: