Airborne, Ship-, and Ground-Based Observations of Clouds, Aerosols, and Precipitation from Recent Field Projects over the Southern Ocean

The Southern Ocean (SO) is a natural laboratory for quantifying marine cloud-aerosol interactions because it is a pristine environment far from continental aerosol sources. Weather and climate models are challenged by uncertainties and biases in simulating SO clouds, aerosols, precipitation and radiation tracing to a poor understanding of the underlying processes and a lack of prior observations. The Southern Ocean Cloud Radiation Aerosol Transport Experimental Study (SOCRATES), the Macquarie Island Cloud Radiation Experiment (MICRE), the Measurements of Aerosols, Radiation and Clouds over the Southern Ocean (MARCUS) and the Clouds Aerosols Precipitation Radiation and Atmospheric Composition over the Southern Ocean (CAPRICORN) projects made extensive measurements of clouds, aerosols and precipitation in a North-South Curtain over the SO between 2016 and 2018. Observations include in-situ measurements of cloud condensation nuclei (CCN), ice nucleating particles (INPs), and cloud and aerosol size-resolved and bulk properties from the NSF/NCAR G-V during SOCRATES, cloud and aerosol remotely sensed properties from sensors on the G-V during SOCRATES, at Macquarie Island during MICRE and on the R/V Investigator and Aurora Australis during CAPRICORN and MARCUS, surface aerosols at Macquarie Island and on the ships, and atmospheric profiles from radiosondes on the ships, at Macquarie Island and the G-V. Synergistically these data provide measurements of the boundary layer and free troposphere structure, together with vertical distributions of liquid and mixed-phase clouds and aerosols over cold waters where supercooled and mixed-phase boundary layer clouds are frequent, including the most comprehensive data south of the oceanic polar front, in the cold drop sector of cyclones, and seasonal variations. Highlights from these campaigns include: measurements of pristine environments with few INP, numerous small and few large aerosols above cloud (suggesting strong new particle formation), and ubiquitous supercooled water in thin, multi-layered clouds with small-scale generating cells near cloud tops. These data are being used to study the dependence of ice and liquid cloud properties on aerosol amounts, wind speeds, coupling of the boundary layer to the clouds, sea surface temperature and position relative to cyclone center; the dependence of icing regions on environmental parameters; and the nature of supercooled and mixed-phase clouds over the SO, including fine-scale transitions between phases. The use of SO data for evaluating and improving models with different spatial and temporal scales will also be discussed.