Sensitivity experiments with ICON-LAM to test probable explanations for higher ice crystal number over Arctic sea ice vs. ocean

Abstract. Arctic warming is causing the sea ice to retreat, exposing larger areas of open ocean. This shift is expected to alter aerosol emissions, potentially influencing cloud microphysics and ratiative properties. Recent studies show that ocean-derived ice nucleating particles are highly efficient in ice nucleation at relatively warm temperatures. However, our previous study, a 10-year analysis of ice crystal number concentration from DARDAR-Nice satellite retrievals revealed higher ice numbers over sea ice compared to open ocean (Papakonstantinou-Presvelou et al., 2022). In the current study we explore potential causal explanations behind this contrast. We perform kilometer scale resolution simulations with the ICON-LAM atmospheric model for a 3-day period in March 2019. We validate the satellite retrievals with recent aircraft in situ observations collected during the AFLUX campaign, finding general agreement in the observed contrast of ice crystal numbers between sea ice and open ocean. Sensitivity experiments investigate three potential mechanisms; enhanced INP concentrations over sea ice, blowing snow particles and secondary ice production (SIP). Our results suggest that both INPs over sea ice and blowing snow particles can explain the observed difference below −10 °C, while secondary ice production cannot account for the difference above −10 °C. We thus conclude that as sea ice retreats in a warming Arctic, the two former processes become less relevant, leading to lower particle concentrations in a future climate.