Characteristics of Rainbands, Radar Echoes, and Lightning near the North Carolina Coast during GALE

Abstract

Characteristics of mesoscale rainbands and echoes in radar reflectivity data recorded during the field phase of the Genesis of Atlantic Lows Experiment (GALE) are presented. The primary sources of data were radar microfilm and manually digitized radar (MDR) reports from the operational National Weather Service (NWS) radars at Cape Hatteras (HAT) and Wilmington (ILM), North Carolina. The dataset also included cloud-to-ground lightning flashes that were recorded by the network operated by the State University of New York at Albany. The analyses included rainbands of at least 90-km length with lifetimes of at least 2 h. Nearly all of the rainbands were within 400 km of synoptic-scale or coastal fronts. Warm-sector rainbands predominated. Rain-bands were clarified by the location of their initial detection relative to the land. coastal shelf, and Gulf Stream. Rainbands were initially identified more frequently over the Gulf Stream and ten often over the coastal shelf than the corresponding fractional arms monitored by the radars. Statistical tests determined significant differences in the sample means of the MDR and lightning data between the Gulf Stream and land regions that were largely a consequence of many more hours with MDR and lightning over the Gulf Stream. Composites relative to the beginning and ending of the rainband cases indicated that differences between the Gulf Stream and land were small shortly after the initial detection of rainbands and large just before the final detection of rainbands. The largest Gulf Stream-land disparities occurred, average, during low-level cold and dry advection at HAT. Trunk and Bosart reported a convective echo maximum over the Gulf Stream near HAT and discussed physical processes that can account for the convective maximum. Analysis of one idealized distribution of convecton, however, supports the likely role of sampling limitations of the NWS radar network in determining the location of the convective echo maximum near HAT.