Polarimetric Cloud Analysis and Seeding Test (POLCAST)
The Polarimetric Cloud Analysis and Seeding Test (POLCAST) was a cloud seeding research experiment that was conducted to help determine if hygroscopic seeding could be detected directly by polarimetric radar observations or through derived polarimetric parameters. 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 – 5 August 2006. The study was centered on the measurements recorded by the University of North (UND) C-Band polarimetric Doppler Radar (NorthPol). Hygroscopic flares, deployed on a Weather Modification Incorporation (WMI) aircraft, were used in the study. Ice Crystal Engineering provided these flares.
From the polarimetric radar observations, liquid water content, rainfall rates and hydrometeor type were analyzed. The radar-estimated liquid water content retrievals indicated an increase in 7 of the 8 cases after hygroscopic seeding. In correspondence, the rainfall rates were also higher along with the durations of the cells in the seeded cases. The differential reflectivity decreased after seeding, which is anindication that rain drops were decreasing on average in size. The reflectivity also increased after seeding except at cloud base where there was a decrease in reflectivity after seeding. The hydrometeor identification results were in good agreement with the trends observed in reflectivity and differential reflectivity fields.