Characteristics of Radar-Identified Big Drop Zones in Swiss Hailstorms

Abstract

The characteristics of the so-called ?radar-identified big drop zones? (rBDZ) have been investigated. The study employs radar observations of several thunderstorms and simultaneous microphysical and vertical wind measurements with a penetrating T-28 aircraft. The comparison of aircraft-measured vertical wind and radar data revealed good coincidence between rBDZs and updraft regions, indicating that this part of the seeding hypothesis upon which Grossversuch IV was based is reasonable. The microphysical observations of rBDZs, however, show large concentrations of ice particles and practically no supercooled raindrops indicating that the latter do not play a significant role in the development of hail in the Swiss storms. There is no reason to believe that directing seeding material into such regions where natural ice already exists in great abundance will have any significant effect an the hail process.