Investigating Secondary Ice Production in Springtime Arctic Mixed-phase Clouds

In the current climate, Arctic mixed-phase clouds (MPCs) have a warming effect on average. While the radiative impact of MPCs is driven by their liquid phase, the formation and growth of ice particles can alter their radiative properties. Ice crystal formation and growth processes in MPCs are still poorly understood, leading to large uncertainties in their representation in weather and climate models, and thus in their role in a rapidly warming Arctic. Contributions from secondary ice production (SIP)---ice formation without ice nucleating particles (INP)---are still poorly constrained.

In this study, we investigate the occurrence of SIP, riming, and aggregation in springtime Arctic MPCs. We use airborne data collected during the (AC)³ field campaigns AFLUX and HALO-(AC)³, conducted near Svalbard in 2019 and 2022, respectively. During both campaigns, in situ cloud probes covered a particle size range from 2.8 µm to 6.4 mm. We derive estimates of rime mass based on particle shape observations. A clustering approach is used to distinguish particle populations dominated by pristine crystals, aggregates, and rimed particles based on their particle size, number concentration, and rime mass.  We investigate the relative occurrence of each class and its dependence on meteorological conditions. SIP events are identified through multimodal particle size distributions with high concentrations of small ice particles (50 µm < diameter < 100 µm). We analyze the occurrence of SIP in terms of meteorological conditions, cloud properties, and particle class (although direct causal links cannot be made based on airborne data alone). This will lead to a better understanding of ice formation and growth in Arctic MPCs and thus helps to improve future modeling efforts.