A Spatial Analysis of Radar Reflectivity Regions within Hurricane Charley (2004)

Abstract

Regions of 35-dBZ radar reflectivity returns are examined within a landfalling hurricane to determine whether these regions are composed of stratiform, convective, or transition-type precipitation. After calculating spatial attributes of the reflectivity regions such as elongation and edge roughness within a GIS, discriminant analysis is performed to determine whether the 35-dBZ regions are more similar to 40-dBZ regions of convective precipitation or to 30-dBZ regions of stratiform precipitation. Results show that within the outer region rainbands of Hurricane Charley (2004) a sharp horizontal reflectivity gradient exists, indicating that 35-dBZ regions are similar in shape to adjacent convective regions of 40-dBZ reflectivity values. Within the interior region, the 35-dBZ regions are identified as transition regions similar to those found within mesoscale convective complexes rather than being strictly stratiform or convective in nature. The rain rates produced by the reflectivity regions are examined using rain gauge and radar estimates. In 32% of cases, the 35-dBZ regions produced rain rates in excess of 10 mm h−1, exceeding both the radar-estimated rain rates and the 8.4 mm h−1 rain rate ascribed to 35-dBZ regions by the tropical Z–R relationship. Thus, 35-dBZ regions surrounding the convective cores of additional landfalling TCs should be examined to determine whether they also represent transition-type rainfall regions capable of producing convective rainfall rates exceeding 10 mm h−1.