An evaluation of phase, aerosol-cloud interactions and microphysical properties of single- and multi-layer clouds over the Southern Ocean using in situ observations from SOCRATES

Single- and multi-layer clouds are commonly observed over the Southern Ocean in varying synoptic settings, yet few studies have characterized and contrasted their properties. This study provides a statistical analysis of the microphysical properties of single- and multi-layer clouds using in-situ observations acquired during the Southern Ocean Cloud-Radiation Aerosol Transport Experimental Study. The relative frequencies of ice-containing samples (i.e., mixed and ice phase) for multi-layer clouds are 0.05-0.25 greater than for single-layer clouds, depending on cloud layer height. In multi-layer clouds, the lowest cloud layers have the highest ice-containing sample frequencies, which decrease with increasing cloud layer height up to the third highest cloud layer. This suggests a prominent seeder-feeder mechanism over the region. Ice nucleating particle (cloud condensation nuclei) concentrations are positively (negatively) correlated with ice-containing sample frequencies in select cases. Differences in microphysical properties are observed for single- and multi-layer clouds. Drop concentrations (size distributions) are greater (narrower) for single-layer clouds compared with the lowest multi-layer clouds. When differentiating cloud layers by top (single- and highest multi-layer clouds) and non-top layers (underlying multi-layer clouds), total particle size distributions (including liquid and ice) are similarly broader for non-top cloud layers. Additionally, drop concentrations in coupled environments are approximately double those in decoupled environments.