Microphysical processes in two tornadic supercells inferred from ARMOR dual-polarimetric radar observations

During the Super-Tuesday tornado outbreak of 5-6 February 2008, eighty-four tornadoes occurred over the Southern United States and the lower Ohio Valley. During the outbreak, two EF-4 tornadoes occurred in Northern Alabama within range of the University of Alabama in Huntsville (UAH) Advanced Radar for Meteorological and Operational Research (ARMOR, C-band dual-polarimetric). The focus of the paper will be on microphysical processes associated with hazardous weather in the two (Lawrence and Jackson County) tornadic supercells as inferred from ARMOR dual-polarimetric radar observations. Special emphasis will be placed on dual-polarimetric radar signatures in the vicinity of the mesocyclone, rear flank downdraft (RFD) and appendage/hook echo regions prior to tornadogenesis. Past research has suggested that hydrometeor type and particle size distribution in the hook echo may play an important role in the thermodynamics of the RFD and tornadogenesis. Dual-polarimetric radar can characterize bulk particle types and provide at least qualitative information regarding particle size and number concentration. For example, a zone of high differential reflectivity and low specific differential phase (likely indicating a relatively small number of large, partially melted hailstones and raindrops) was persistently located in the reflectivity appendage associated with the RFD of the Lawrence County tornadic supercell prior to tornadogenesis. According to past research, the presence of small numbers of large raindrops within the RFD may have played a key role in tornadogenesis. As a result, the four-dimensional structure of the dual-polarimetric variables in the appendage will be placed in the context of single Doppler velocity data and the tornado track. In addition, dual-polarimetric radar signatures of size sorting associated with large hail (reports up to 1.75 inch or 4.4 cm) and extremely heavy rain (up to 200 mm/h) were readily apparent in the forward flank downdraft (FFD) of the Lawrence County supercell. Similar microphysical processes will be investigated for the Jackson County tornadic supercell later on the same day.