3D Convective/Stratiform Echo Type Classification and Convectivity Retrieval from Radar Reflectivity

Michael Dixon, Ulrike Romatschke 

The newly developed ECCO (Echo Classification from COnvectivity) algorithm identifies convective and stratiform types of radar echo in three dimensions. It is based on the calculation of reflectivity texture - a measure of the heterogeneity of the radar echoes on each horizontal plane in a 3D Cartesian volume. Reflectivity texture is translated into convectivity, which is a newly invented quantitative measure of the convective nature of each three dimensional radar grid point. It ranges from 0 (100% stratiform) to 1 (100% convective). By thresholding convectivity, a more traditional qualitative categorization is obtained which classifies radar echoes as convective, mixed, or stratiform. In contrast to previous algorithms, these echo type classifications are provided on the full three dimensional grid of the observed reflectivity field. The vertically resolved classifications, in combination with temperature data, allow for sub-classifications into shallow, mid, deep, and elevated convective features, and low, mid, and high stratiform regions - again in three dimensions.
The algorithm was validated using datasets collected during the PECAN field campaign, which took place over the US Great Plains in 2015. An analysis of lightning counts shows that the majority of lightning flashes occur in regions classified as deep convective features by ECCO. A statistical comparison of ECCO echo types with the well established GPM radar precipitation type categories show strong agreement. ECCO was also applied to radar grids for the Continental US, the United Arab Emirates, Australia, and Europe, illustrating its robustness and adaptability.