Polarimetric Radar Analysis of Hygroscopic Seeding of Clouds in Eastern North Dakota

The Polarimetric Cloud Analysis and Seeding Test (POLCAST) is an ongoing field program with the goal to better understand the effects of hygroscopic cloud seeding at cloud base on convective clouds in Eastern North Dakota. Specifically, POLCAST is focused determining if identifiable signatures of hygroscopic seeding can be observed in polarimetric observables or derived fields. POLCAST is a cooperative study between the North Dakota Atmospheric Resource Board (NDARB), National Center for Atmospheric Research (NCAR), University of North Dakota (UND), and Weather Modification Inc. (WMI). The field program has been conducted for three summer convective seasons (July-August 2006, June-July 2008, and June-July 2010). The main observation platform for the study has been the UND C-Band Polarimetric Doppler Weather Radar (NorthPol). NorthPol has collected a variety of radar observables, which included radar reflectivity, Doppler velocity, differential reflectivity, differential phase, specific differential phase, and correlation coefficient. In conjunction with NorthPol scanning, a WMI aircraft has been used for targeting the clouds and has collected basic aerosol and microphysical measurements. For the most recent field program (POLCAST3), the UND Citation research aircraft was used to collect in situ cloud observations. This paper focuses on radar data analyses of the randomized seeding cases from POLCAST2 and POLCAST3. A total of 13 cases were collected in POLCAST2 in 2008. An additional 14 cases were collected during 2010 field season (POLCAST3). The radar analysis has focused on applying the NCAR hydrometeor identification (HID) algorithm tuned for C-band observations. Also, for each case, seeded and non-seeded cells are being categorized and a statistical and physical characteristic database is being created. This presentation gives a brief description of the experiment and a summary of the key results of the randomized seeding analysis.