Natural marine cloud brightening in the Southern Ocean

• Published in: Atmospheric Chemistry and Physics
• Main Authors: G. G. Mace, S. Benson, R. Humphries, P. M. Gombert, E. Sterner
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2023
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Antarctic; Southern Ocean; The Antarctic; Antarc*
• Online Access: https://doi.org/10.5194/acp-23-1677-2023; https://doaj.org/article/0b2d783d9abb4ef09bcf79ce9d20e21d

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 a direct correlation to marine primary productivity (PP) because of the role of seasonally varying, biogenically derived precursor gases 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 environments. Here, we examine N d variability derived from 5 years of MODIS Level 2-derived cloud properties in a broad region of the summer eastern Southern Ocean and adjacent marginal seas. We demonstrate latitudinal, longitudinal and temporal gradients in N d that are strongly correlated with the passage of air masses over high-PP waters that are mostly concentrated along the Antarctic Shelf poleward of 60 ∘ S. We find that the albedo of MBL clouds in the latitudes south of 60 ∘ S is significantly higher than similar liquid water path (LWP) clouds north of this latitude.