Initial Performance Evaluation of a Radar-Based Super-Cooled Water Detection Algorithm during the SNOWIE Field Campaign

An algorithm called the 'Radar Icing Algorithm' (RadIA) has been developed at the National Center for Atmospheric Research to detect the presence, phase components and relative size of supercooled drops. Raw dual-polarization radar moments and a numerical weather prediction model temperature profile are first ingested. Radar moment values are quality-controlled to exclude clutter, biological targets, anomalous returns and above-freezing regions, and the temperature profile is adjusted based on the detected height of the melting level. Locations that have sub-freezing temperatures and valid radar return then have calculations performed in real-time for every pixel within a given radar's native polar coordinate volume. The calculations result in a 0 to 1 interest value output which estimates the potential for the presence of small-drop, large-drop, mixed-phase and plate-shaped crystals.

During the recent 'Seeded and Natural Orographic Wintertime Clouds: The Idaho Experiment' (SNOWIE) Field Campaign, a large host of ground-based meteorological instrumentation were sited in and around the Payette River Basin, just north of Boise, Idaho. The instrument array included seven multi-channel passive radiometers, two Doppler X-band radars, one operational S-band radar, multiple precipitation gauges, regular radiosonde releases, and twelve radiosondes coupled with vibrating wire sondes for supercooled liquid water content profiling. Two instrumented research aircraft, the University of Wyoming KingAir and the Weather Modification International KingAir, flew over one-hundred and thirty combined hours during twenty-four intensive operations periods from January to March of 2017. During this field campaign, a wide array of in-flight icing conditions were observed and thoroughly sampled, including homogeneous small and large drops, mixed-phase, graupel, icing in stratiform and convective environments, and a few null icing cases.

In this study, RadIA interest values from several SNOWIE cases are matched to values of liquid water content from research aircraft flight segments during straight-and-level operations. A statistical analysis will be presented demonstrating how well the radar-based interest fields correlate to known small-drop, large-drop, and mixed-phase conditions.

Although the FAA has sponsored this project, it neither endorses nor rejects the findings of the research. The presentation of this information is in the interest of invoking technical community comment on the results and conclusions of the research.