Microphysical Properties of Supercooled Large Droplet Conditions in North America and Europe

Abstract

Supercooled large droplet (SLD) icing conditions threaten aviation safety. Two flight campaigns in SLD conditions were performed in February–March 2023 in the Great Lakes region and in April 2023 over France as part of the EU project SENS4ICE. This provides the opportunity to contrast and compare the observations of SLDs between these two locations and months. We present the altitudes, temperatures, number concentrations, liquid water contents, and cumulative mass distributions of the SLD conditions. During the North American flight campaign, SLD conditions were observed mostly in thick stratus clouds, and droplet size distributions were bimodal with an average median volume diameter (MVD) of 23 μm. Due to warmer ground temperatures in April, icing conditions during the European campaign occurred at higher altitudes; hence, predominantly midlevel clouds were sampled. The average MVD of SLD conditions was 45 μm. Our study suggests that the maritime origin of the European air masses, their likely low levels of pollution, and the associated low number of cloud condensation nuclei facilitated the formation of these SLD conditions with relatively large MVDs. The presented dataset can serve for model comparisons, process-oriented studies of icing conditions, and the validation of airborne sensors developed in the Sensors and Certifiable Hybrid Architectures for Safer Aviation in Icing Environment (SENS4ICE) project.