Unique Microphysical Properties of Small Boundary Layer Ice Particles under Pristine Conditions on Dome C, Antarctica

Abstract. The Antarctic plateau, one of the coldest and cleanest regions of our planet, experiences almost exclusively frozen precipitation. Understanding the microphysical properties of inland Antarctic boundary layer ice particles with sizes below a few hundred micrometers is essential to improve atmospheric models and accurately validate remote sensing data for this region. Currently, only a small number of in situ atmospheric measurements exist for particle sizes smaller than 100 μm on the Antarctic plateau, performed over short measurement times. We present the first multi-week study of optical in situ measurements of boundary layer ice particle size, shape and morphological complexity for sizes down to 11 μm with a temporal resolution in the order of minutes, including a multi-day ice fog event. Classifying cirrus ice fog events with a lidar system, we found mean particle sizes smaller than 11 μm for ice fog events and of about 70 μm for cirrus precipitation and diamond dust events. The mean particle concentration of the ice fog at Dome C (3.9 L−1) is found to be lower than commonly used parametrisations of Arctic ice fog and lower than the concentration of anthropogenically influenced urban ice fog measured at Fairbanks, Alaska during a three-year study with the same instrument (350 L−1). Moreover, ice fog particles at Dome C are found to be more pristine than at Fairbanks. Therefore, Antarctic boundary layer ice particles need to be parametrized differently than their Arctic counterparts due to distinct conditions on the Antarctic plateau.