Intercomparison of NEXRAD rainfall estimates and raingauge measurements for GCIP

The US National (NEXRAD) Radar Network, covering almost the entire conterminous US, provides a unique tool for hydrometeorological and hydroclimatological research. Composite reflectivity data from the NEXRAD network are being used to compile a 5-year continental-scale database of radar rainfall estimates at a 4 x 4 km spatial resolution and a 1-hour time resolution. To assess the quality of this database, we carry out special projects at different radar sites around the country, where we perform detailed comparisons between the composite reflectivity data, the archived volume-scan reflectivity data and data from dense networks of raingauges. Often these are complemented with disdrometer data, lightning data and storm tracking analyses. Here, we report on one such special project, namely for the southern Appalachian region of the southeastern US.

The rugged local topography (Appalachian Mountains, maximum elevations 2000-2500 m) and the intense warm season rainfall in this region (induced by orographic convection) make this a challenging site, both from an operational radar perspective and from a hydrometeorological perspective. Moreover, the availability of rainfall data from dense raingauge networks (the IFLOWS network over southwestern North Carolina and the USGS network over the Charlotte, North Carolina urban area) allow detailed intercomparisons. We present such intercomparisons between the composite reflectivity data and the volume scan reflectivity data on the one hand and between the volume scan data and the raingauge data on the other hand, for the warm season precipitation of 1999 and 2000. These intercomparisons are supported by analyses of disdrometer data and lightning data (providing information about the microphysics of orographic convection) as well as storm tracking analyses (providing information about the dynamics).