18 Aug 2022
18 Aug 2022
Status: this preprint is currently under review for the journal ACP.

Natural Marine Cloud Brightening in the Southern Ocean

Gerald G. Mace1, Sally Benson1, Ruhi Humphries2,3, Mathew Peter Gombert1, and Elizabeth Sterner1 Gerald G. Mace et al.
  • 1Department of Atmospheric Sciences, University of Utah, Salt Lake City, Utah
  • 2Climate Science Centre, CSIRO Oceans and Atmosphere, Melbourne, Australia
  • 3Australian Antarctic Program Partnership, Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia

Abstract. The number of cloud droplets per unit volume (Nd) 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 Nd 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 Nd 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 Nd 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.

Gerald G. Mace et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-571', Anonymous Referee #1, 07 Sep 2022
  • RC2: 'Comment on acp-2022-571', Anonymous Referee #2, 09 Sep 2022

Gerald G. Mace et al.

Gerald G. Mace et al.


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Short summary
The number cloud droplets per unit volume is a significantly important property of clouds that controls their reflective properties. Computer models of the Earth's atmosphere and climate have low skill at predicting the reflective properties of Southern Ocean clouds. Here we investigate the properties of those clouds using satellite data and find that the cloud droplet number in the Southern Ocean is related to the oceanic phytoplankton abundance near Antarctica.