Simulated Polarimetric Radar Fingerprints of Ice Growth in Arctic Mixed-Phase Clouds

Mixed-phase clouds are observed frequently in the Arctic, often persisting for several days. These systems can have large impacts on the Earth's radiative budget and, given the lower number concentrations of ice particles compared to those found in mid-latitude systems, allow us to study microphysical processes such as vapor deposition, riming, and aggregation in their more isolated and early stages. We compare polarimetric radar observations of pure vapor depositonal growth from the Atmospheric Radiation Measurement site at Oliktok Point, AK with microphysical model simulations of vapor deposition to better understand how this process impacts the radar observations within Arctic mixed-phase clouds. We show simulations using a bin microphysical model with adaptive habit prediction, where aspect ratio and density evolve according to temperature and supersaturation. This model operates in a two dimensional kinematic framework so that only the microphysical processes impact precipitation growth, and is initialized with representative atmospheric profiles of temperature and humidity. The model produces qualitatively similar enhancements in differential reflectivity, specific differential phase, and the vertical gradient in the radar reflectivity factor to the observations. Given the large uncertainties in our assumptions for the polarimetric radar forward model, we use a variety of methods for computing the radar variables and estimate their potential errors. The feasibility of evaluating simulations of riming and/or aggregation is also discussed.