Polarimetric Radar Analysis of Hygroscopic Seeding

The Polarimetric Cloud Analysis and Seeding Test (POLCAST) was a research project designed to help determine if hygroscopic seeding could be detected by polarimetric radar observables (e.g. differential phase, differential reflectivity, etc.) or derived radar fields. The experiment was conducted on convective systems that were observed in Eastern North Dakota. The operational phase of the program, a cooperative study between the North Dakota Atmospheric Resource Board (NDARB), University of North Dakota, Weather Modification Inc., and Ice Crystal Engineering, was conducted from 10 July to 5 August 2006. The University of North Dakota (UND) C-Band Polarimetric Doppler Radar (NorthPol) collected a variety of radar observables, which included radar reflectivity, Doppler velocity, differential reflectivity, differential phase, specific differential phase, and correlation coefficient. From the radar observations, rain water content (RWC), rainfall rates, differential reflectivity and hydrometeor type were analyzed.

The results indicate that the RWC on average shows an increase after hygroscopic seeding. The rainfall rate analysis also showed positive results with an increase in average maximum rain rate and rain duration. Based on all these preliminary results, there is indication that polarimetric radar can observe the effects of hygroscopic seeding. In summary, a brief description of the experiment along with highlights of the key results will be discussed in the presentation.