Characterizing secondary ice production events in mixed-phase clouds using ground-based polarimetric radar

Secondary ice production processes are widely proposed as the pathway by which observed cloud ice number concentration can markedly exceed what is expected from primary ice nucleation alone. These processes play a critical, yet poorly constrained, role in the lifecycle of mixed-phase clouds. Presently, main constraints on secondary ice production come from airborne observations, but the transiency of such observations makes it difficult to paint a complete picture of these processes. Here, we develop a novel method for retrieving ice number concentration in a Lagrangian reference frame, allowing us to unearth information not accessible from existing aircraft observations. Our retrieval method employs an iterative ensemble approach, advanced ice crystal models, and the traditional suite of polarimetric radar observables. We will present examples from the Atmospheric Radiation Measurement (ARM) program Mobile Facility deployment in Finland and evaluations against in-situ observations from the UK Parameterizing Ice Clouds using Airborne obServationS and triple-frequency dOppler radar data (PICASSO) field campaign. We will also present a climatology of cloud ice number concentration from the Finland campaign, shedding light on the spatiotemporal evolution, process rates, and trigger requirements of secondary ice production events.