Natural Marine Cloud Brightening in the Southern Ocean

• Main Authors: Mace, Gerald G., Benson, Sally, Humphries, Ruhi, Gombert, Mathew Peter, Sterner, Elizabeth
• Format: Text
• Language: English
• Published: 2022
• Subjects: Antarctic; Southern Ocean; The Antarctic; Antarc*
• Online Access: https://doi.org/10.5194/acp-2022-571; https://acp.copernicus.org/preprints/acp-2022-571/

The number of cloud droplets per unit volume ( N d ) is a fundamentally important property of marine boundary layer (MBL) liquid clouds that, at constant liquid water path, exerts considerable controls on albedo. Past work has shown that regional N d has direct correlation to marine primary productivity (PP) because of the role of seasonally-varying biogenically-derived precursor gasses in modulating secondary aerosol properties. These linkages are thought to be observable over the high latitude oceans where strong seasonal variability in aerosol and meteorology covary in mostly pristine marine environments. Here, we examine N d variability derived from five years of MODIS level 2 derived cloud properties in a broad region of the summertime Eastern Southern Ocean and adjacent marginal seas. We demonstrate both latitudinal, longitudinal, and temporal gradients in N d that are strongly correlated with the passage of air masses over regions of high PP waters that are mostly concentrated along the Antarctic Shelf poleward of 60° S. In particular we find that the albedo of MBL clouds in the latitudes south of 60° S is significantly higher than similar LWP clouds north of this latitude.