Report on the Polarimetric Cloud Analysis and Seeding Test 3 (POLCAST3) Field Project

Abstract: The Polarimetric Cloud Analysis and Seeding Test 3 (POLCAST3) experiment is a continuation of the original 2006 and 2008 field programs. The project's main objective is to better understand the effects of hygroscopic cloud seeding at cloud base on convective clouds in North Dakota. The 2010 project was conducted between June 21 and July 23 2010 and had five different components. 1.) Cloud seeding and aerosol measurements using a Cessna 340 aircraft. 2.) Measurements using the University of North Dakota (UND) Polarimetric Doppler Weather Radar. 3.) In situ cloud microphysical sampling using the instrumented UND Citation Research Aircraft. 4.) Surface aerosol measurements in Grand Forks, North Dakota. 5.) Special Weather Research and Forecasting (WRF) model runs for the project area.

The Cessna 340 aircraft carried an Aircraft Temperature Sensor, Passive Cavity Aerosol Spectrometer Probe, and Cloud Condensation Nuclei Counter. The seeding aircraft flew eleven flights (26.2 hours) with a total of thirteen hygroscopic seeding targets found. Throughout the POLCAST3 project, the UND radar was operated to help understand the natural characteristics of clouds in the region and for assessing potential effects from hygroscopic seeding. Radar data was collected and archived using the Interactive Radar Information System (IRIS) software package. The IRIS software was used to generate and create real time display products that were posted to the Web. Additionally, the radar data and seeding aircraft flight tracks were incorporated in the Thunderstorm Identification Tracking Analysis and Nowcasting (TITAN) and Configurable Interactive Data Display (CIDD) software packages for real time display and post field project analysis. The UND Citation Research carried a set of basic meteorological and cloud physics instruments, which included the Droplet Measurement Systems (DMT) Cloud Droplet Probe to measure the cloud size distribution between 3 and 50 µm which enable determination of the change in effect radius with height above cloud base. The UND Citation Research Aircraft flew five flights (7.6 hours) sampling cloud properties above seeding targets. Surface based aerosol measurements that include cloud condensation nuclei measurements were made on the top of Clifford Hall on the University of North Dakota campus. Comparison between surface and cloud based measurements are important to understanding how aerosol measurements can be incorporated into operational programs. WRF model runs were initialized twice per day at 00 Z and 12 Z using cold start initialization. Three nested domain (27, 9 and 3 km) were used with the 3 km inner domain centered on the North Dakota project area. The WRF model was actively used for forecasting during the project and radar data will be used to evaluate WRF convective products.