Life cycle of ice-nucleating particles in an Arctic cold air outbreak

Ice-nucleating particles (INPs) can modulate the cloud-phase feedback, where the albedo of mixed-phase clouds increases in a warming climate. Mid-to-high latitude shallow cloud systems such as cold-air outbreaks (CAOs) are particularly important for cloud-phase feedbacks and sensitive to INPs. While previous studies have looked at the impact of INP concentration on CAOs, few studies have considered the life cycle of INPs in cold-air outbreaks, and the consequences for cloud albedo.

To understand how INPs are processed in CAOs, we are performing regional modelling of a CAO observed over the Norwegian Sea during the 2022 Arctic Cold Air Outbreak field campaign. Airborne INP measurements during this CAO revealed a reduction in INP concentration as the CAO developed despite the addition of sea-spray aerosol downstream in the outbreak (Raif, et al. 2024). We will test the hypothesis that INPs in air flowing into Arctic CAOs initially overwhelms local surface sources of aerosol, but are removed through precipitation processes as air moves south.

To do this, we are using the UK Met Office Unified Model with a new two-moment microphysics scheme utilising two-way interaction between cloud and aerosol tracers. Using in-situ measurements of aerosol and INPs, we will test the sensitivity of CAO development to the entrainment of INPs, removal of INPs through precipitation and redistribution of INPs after sublimation/evaporation.

Reference: Raif, et al. (2024). High ice-nucleating particle concentrations associated with Arctic haze in springtime cold-air outbreaks, Atmos. Chem. Phys. https://doi.org/10.5194/acp-24-14045-2024