Persistent Supercooled Liquid Water in the North Atlantic and Southern Ocean

The low and mid-level clouds that form within cold air outbreaks significantly increase Earth’s albedo. These clouds frequently occur in mixed-phase temperature ranges, and their radiative properties are largely controlled by the amounts of liquid water and ice they contain as well as their cloud-top phases. Thus, quantifying Earth’s albedo in present and future climates requires understanding how ice forms and evolves within these bright clouds. However, glaciation in mixed-phase marine clouds is poorly understood, and cloud phase is difficult to measure with remote sensing instruments. Until recently, few in situ datasets existed for the remote oceanic regions associated with the highest cloud cover. Here, we compare in situ observations and high resolution simulations for two recent field campaigns in the North Atlantic and the Southern Ocean. We evaluate the relative roles of dynamics and microphysics in determining the observed amounts of liquid water and ice condensate.

We simulate a well-studied case from the CONSTRAIN field campaign of a stratocumulus to cumulus transition in the North Atlantic with persistent supercooled liquid water (SLW). We find that the simulation reproduces the observed SLW and shows little sensitivity to microphysical parameters, including fixed droplet concentration and the number of ice nucleating particles. Next, we will simulate cases from The Southern Ocean Clouds Radiation and Aerosols Transport Experiment (SOCRATES), which sampled cold sector clouds for six weeks during the Austral summer of 2018, and observed persistent SLW as cold as -30°C. This analysis will provide a foundation for improving the representation of mixed-phase marine clouds in global climate models.