An Updated Rain-Type (Convective-Stratiform) Classification for Rain-Rate Estimation and Identifying Shallow Convection

The well-known Steiner et al. (1995) algorithm for identifying convective and stratiform precipitating elements in tropical convection has been updated. Two primary features are new to the algorithm: 1) It identifies echo surrounding convective cores as “mixed” regions based on the hybrid convective/stratiform heating profiles in such regions, and 2) It separately classifies isolated convection, which is often shallow, from deeper, more intense convection. The cores of isolated convection are further separated from the edges of such echo objects. Thus the new algorithm contains five precipitating echo categories: Convective, stratiform, mixed, isolated convective core, and isolated convective fringe. The accuracy of the classification algorithm in a composite sense is verified using simulated heating profiles of precipitating columns for the different categories when the algorithm is run on radar reflectivity as simulated by WRF model representations of tropical maritime convection. When run on the lowest available elevation angle of radar data in its native polar coordinate system, the updated algorithm successfully identifies shallow convection not detected by the Steiner et al. algorithm. Regardless of the elevation used, the updated algorithm identifies the edges of isolated convection as “isolated convective fringe” instead of “stratiform”. Rain-type classifications can then be used to aid rainfall estimation, and we present rain rate estimates for data collected during the DYNAMO field campaign from the C-band radar aboard the R/V Revelle and the dual-pol S-band radar at Addu Atoll. Roughly 52%, 12%, 22%, 9%, and 5% of the rainfall by volume during DYNAMO was attributed to convective, stratiform, mixed, isolated core, and isolated fringe echoes respectively.