Diurnal variation of the planetary boundary layer over Dome C (Antarctica) impacting the formation of supercooled liquid water clouds

While the majority of Antarctic clouds are made up of ice crystals, a significant proportion consists of supercooled liquid water (SLW), defined as water in liquid form below 0 °C. Observations of SLW clouds have been carried out for several years at Dome C, the Concordia station (75° S, 123° E; 3233 m above mean sea level), combining observations from LIDAR, microwave radiometer and balloon-borne sondes. The present analysis is separated in two parts. Firstly, we will focus on the diurnal variation of the planetary boundary layer (PBL) from balloon-borne profile observations performed on January 23, 2023 establishing the presence of SLW clouds: 1) at the top of the PBL between the entrainment zone and the capping inversion layer, 2) higher up within a fossil layer, and 3) within the very cold stable boundary layer close to the surface as liquid fog. Secondly, from a statistical study covering several summer periods, we will show that SLW clouds are present from 400 to 600 m above ground level (agl) in the entrainment zone and within the stable boundary layer below 100 m agl where liquid fog can form, with temperatures from −25 °C to −35 °C and LWP (liquid water path, the vertically-integrated SLW content) less than 3.0 g m−2.