Retrieving Cloud Ice Number Concentration From Polarimetric Radar

Abstract:

The collective spatiotemporal evolution of ice particle populations within a cloud can fundamentally change its radiative properties, precipitation efficiency, and thus lifetime. The associated microphysical processes; such as pristine ice depositional growth, aggregation, and sedimentation have long been studied using polarimetric radar observations, but radar returns can be ambiguous in the presence of heterogenous hydrometeor populations. It remains challenging to separate signals between hydrometeor species and characterize their microphysical properties robustly. Here, we introduce a method for retrieving properties of pristine ice and aggregates in heterogenous scenes using measurements from ground-based X-band scanning polarimetric radar. This method is built on a novel retrieval framework, exploiting the unique scattering properties of pristine ice and aggregates via an iterative ensemble approach. We will detail the method and evaluate our retrievals against in-situ observations from the UK Parameterizing Ice Clouds using Airborne obServationS and triple-frequency dOppler radar data (PICASSO) campaign. We will also present the Lagrangian evolution of pristine ice number concentration at high spatiotemporal resolution using observations from the Biogenic Aerosols – Effects on Clouds and Climate campaign in Finland, an Atmospheric Radiation Measurement (ARM) Mobile Facility deployment. The special Lagrangian view provides an excellent opportunity to study ice multiplication processes and their trigger requirements.