The use of the Storm-Structure-Severity method for improved hailfall estimation in South Africa

The storm-structure-severity(SSS) method is used to identify the structural characteristics of convective storms by making use of volume scanned reflectivity data from the weather radar network. This operational radar scheme, which had been integrated with the TITAN radar storm tracking and display system, identifies the existence of reflectivity overhangs and bounded weak echo region (BWER) within 100 km range from the radar. It also assists in differentiating warm tropical convective storms from storms in a baroclinic environment.

Hail kinetic energy(HKE) is derived using an empirical relationship based on radar reflectivity at an altitude level. This method often leads to overestimation of HKE at the ground, largely due to the inclusion of high rainfall rates as a result of warm rain processes. The use of the SSS field can greatly assist in reducing this overestimation, by identify the structure of the storm which produces high radar reflectivity. Thereby, the non hail producing storm cells are filtered from HKE estimation. Comparisons are made by using various reflectivity thresholds as well as the SSS filtered field for HKE estimation and crop damage reports.