Natural marine cloud brightening in the Southern Ocean

Mace, Gerald G.; Benson, Sally; Humphries, Ruhi; Gombert, Peter M.; Sterner, Elizabeth

doi:https://doi.org/10.5194/acp-23-1677-2023

Articles | Volume 23, issue 2

https://doi.org/10.5194/acp-23-1677-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-23-1677-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 23, issue 2

ACP Letters

| Highlight paper

|

01 Feb 2023

ACP Letters | Highlight paper |

| 01 Feb 2023

Natural marine cloud brightening in the Southern Ocean

Gerald G. Mace, Sally Benson, Ruhi Humphries, Peter M. Gombert, and Elizabeth Sterner

Data sets

Moderate-resolution Imaging Spectroradiometer (MODIS) Terra Chlorophyll Data; 2018 Reprocessing NASA Goddard Space Flight Center, Ocean Ecology Laboratory, and Ocean Biology Processing Group https://doi.org/10.5067/TERRA/MODIS/L3M/CHL/2018

MODIS Atmosphere L2 Cloud Product (06_L2) S. Platnick, S. Ackerman, M. King, et al. https://doi.org/10.5067/MODIS/MOD06_L2.006

Moderate-resolution Imaging Spectroradiometer (MODIS) Aqua Chlorophyll Data NASA Goddard Space Flight Center, Ocean Ecology Laboratory, and Ocean Biology Processing Group https://doi.org/10.5067/AQUA/MODIS/L3M/CHL/2022

CERES Single Scanner Footprint (SSF) TOA/Surface Fluxes, Clouds and Aerosols Edition 4A NASA Langley Atmospheric Science Data Center DAAC https://doi.org/10.5067/AQUA/CERES/SSF-FM3_L2.004A

MODIS Geolocation Fields Product MODIS Characterization Support Team (MCST) https://doi.org/10.5067/MODIS/MOD03.061

Model code and software

IDL Code for: "Natural marine cloud brightening in the Southern Ocean." Atmospheric Chemistry and Physics G. G. Mace, S. Benson, R. Humphries, P. M. Gombert, and E. Sterner https://doi.org/10.7278/S50d-bpx8-gmtt

Executive editor

The Southern Ocean can be considered a region exhibiting pristine conditions as during the pre-industrial time. Thus, any changes in radiative forcing in this region can be attributed to natural factors. Feedbacks of ocean biological activity on Earth’s radiation budget have been put forward as the CLAW hypothesis (Charlson et al., 1987, https://www.nature.com/articles/326655a0). It implies that emissions of biogenic sulfur-containing compounds result in the formation of cloud condensation nuclei, which lead to higher cloud droplet number concentrations. Such clouds are more reflective and thus lead to a cooling effect. The current study provides satellite-based evidence of the increase droplet number concentrations and cloud reflectivity (‘albedo’) triggered by chlorophyll emissions, as a proxy for biological activity. Specifically, it demonstrates for the first time the extent to which the cloud albedo is modulated by biological factors as a function of latitude along the Antarctic shelf. While the study does not extend to discussing the subsequent feedbacks of cloud reflectivity to biological activity, it clearly demonstrates how biological ocean activity affects cloudiness above the Southern Ocean and thus may regulate temperature.