Multifrequency Radar Reflectivity Analysis of Seeded Orographic Winter Clouds

An outstanding question in glaciogenic cloud seeding regards the changes in size distribution and number concentration of ice particles. Concentrations of AgI nuclei vary by orders of magnitude across a seeding plume. The hypothesis we aim to test is that the high concentration of AgI-induced ice crystals in the core of plumes leads to numerous, small particles, while the plume margins contain incrementally fewer, but larger snowflakes. Unprecedented airborne and ground-based radar data were collected of glaciogenically seeded patches of supercooled liquid clouds during the 2017 Seeded and Natural Orographic Wintertime clouds—the Idaho Experiment (SNOWIE). W- and Ka-band profiling radars operated on the University of Wyoming King Air (together with several particle imaging probes), and a X-band Doppler-on-Wheels radar conducted close-range RHIs along the UWKA flight track. All three radars have different range-dependent footprints, but the data can be interpolated to a common grid with horizontal and vertical resolution corresponding to that of the coarsest resolution. Differences in radar reflectivity (dual wavelength ratio) can be attributed to differences in particle scattering across the Rayleigh-Mie transition zone (as well as to differences in path-integrated attenuation), and thus particle size information can be extracted. The objective of this talk is to discuss the multi-frequency analysis method, and to use this method to test the hypothesis, using data from SNOWIE and its predecessor campaign, ASCII (AgI Seeding Cloud Impact Investigation).