Tornadic Behavior Related to Land-Falling Tropical Cyclones in the United States

The 2004 and 2005 North Atlantic hurricane seasons were among the most active and economically devastating for the United States, during which 18 tropical cyclones (TCs) made landfall. These TCs were analyzed using the International Best Tracks Archive for Climate Stewardship (IBTrACS) and Local Storm Reports (LSR) datasets to determine whether they produced tornadoes within a preferred quadrant and distance from the center of circulation of the TC. The land-falling TCs were tracked and analyzed through their weakening stages with tornado reports being classified based on the strength of the TC at the time of occurrence. Tornado reports were not included after the TC was classified as extratropical in the IBTrACS dataset. Over half of all tornado reports occurred when the TCs were rated at or below tropical storm strength. As expected, the northeast quadrant was the most dominate area where tornadic activity occurred. In addition, there were three distinct peaks in tornadic activity at distances of 75-100nm, 175-200nm, and 325-375nm from the center of the circulation. Another emphasis of this work used NEXRAD data to determine the best method of identifying potential tornadic storms within land-falling TCS. The most reliable radar product for the three TCs investigated was velocity couplets

Tornadic Behavior Related to Land-Falling Tropical Cyclones in the United States

The 2004 and 2005 North Atlantic hurricane seasons were among the most active and economically devastating for the United States, during which 18 tropical cyclones (TCs) made landfall. These TCs were analyzed using the International Best Tracks Archive for Climate Stewardship (IBTrACS) and Local Storm Reports (LSR) datasets to determine whether they produced tornadoes within a preferred quadrant and distance from the center of circulation of the TC. The land-falling TCs were tracked and analyzed through their weakening stages with tornado reports being classified based on the strength of the TC at the time of occurrence. Tornado reports were not included after the TC was classified as extratropical in the IBTrACS dataset. Over half of all tornado reports occurred when the TCs were rated at or below tropical storm strength. As expected, the northeast quadrant was the most dominate area where tornadic activity occurred. In addition, there were three distinct peaks in tornadic activity at distances of 75-100nm, 175-200nm, and 325-375nm from the center of the circulation. Another emphasis of this work used NEXRAD data to determine the best method of identifying potential tornadic storms within land-falling TCS. The most reliable radar product for the three TCs investigated was velocity couplets

Measurements of Differential Reflectivity in Snowstorms and Warm Season Stratiform Systems

The organized behavior of differential radar reflectivity (ZDR) is documented in the cold regions of a wide variety of stratiform precipitation types occurring in both winter and summer. The radar targets and attendant cloud microphysical conditions are interpreted within the context of measurements of ice crystal types in laboratory diffusion chambers in which humidity and temperature are both stringently controlled. The overriding operational interest here is in the identification of regions prone to icing hazards with long horizontal paths. Two predominant regimes are identified: category A, which is typified by moderate reflectivity (from 10 to 30 dBZ) and modest +ZDR values (from 0 to +3 dB) in which both supercooled water and dendritic ice crystals (and oriented aggregates of ice crystals) are present at a mean temperature of −13°C, and category B, which is typified by small reflectivity (from −10 to +10 dBZ) and the largest +ZDR values (from +3 to +7 dB), in which supercooled water is dilute or absent and both flat-plate and dendritic crystals are likely. The predominant positive values for ZDR in many case studies suggest that the role of an electric field on ice particle orientation is small in comparison with gravity. The absence of robust +ZDR signatures in the trailing stratiform regions of vigorous summer squall lines may be due both to the infusion of noncrystalline ice particles (i.e., graupel and rimed aggregates) from the leading deep convection and to the effects of the stronger electric fields expected in these situations. These polarimetric measurements and their interpretations underscore the need for the accurate calibration of ZDR.United States. Federal Aviation Administration (Air Force Contract FA8721-05-C-0002