Observations Indicate That Clouds Amplify Mechanisms of Southern Ocean Heat Uptake

Journal Article · 15 February 2022 · Journal of Geophysical Research: Atmospheres

DOI: https://doi.org/10.1029/2021JD035487 · OSTI ID:1845180

Morrison, Ariel L.  ^[1]; Singh, Hansi A.  ^[1]; Rasch, Philip J.  ^[2]

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1. School of Earth and Ocean Sciences University of Victoria Victoria BC Canada
2. Atmospheric Sciences and Global Change Division Pacific Northwest National Laboratory Richland WA USA

Abstract The Southern Ocean has absorbed most of the excess heat associated with anthropogenic greenhouse gas emissions. Since Southern Ocean observations are sparse in certain regions and seasons, much of our knowledge of ocean heat uptake is based on climate model simulations. However, climate models still inadequately represent some properties of Southern Ocean clouds, and they have not identified the mechanisms by which clouds may affect Southern Ocean heat uptake (SOHU). Here, we use the ERA5 and JRA‐55 reanalyses to assess the influence of clouds and other atmospheric processes on SOHU from 1979 to 2020. We find that years with the highest SOHU between 45° and 65°S are dominated by ocean heat uptake anomalies during winter and spring, but not during summer or fall. Winter and spring cloud cover are up to 7% higher when SOHU is up to 5.5 W/m ² higher than the climatological seasonal mean, with the largest increases in the South Pacific Ocean. Clouds also contain more liquid water. These changes in cloud properties increase downwelling longwave radiation, amplifying ocean heat uptake. Cloud changes are also concomitant with a more stable lower atmosphere, which suppresses turbulent heat fluxes out of the surface. Overall, we find that SOHU is likely not mediated by enhanced surface shortwave absorption over the observational time period. A better understanding of how atmospheric processes impact ocean heat uptake may help improve our understanding of ocean heat uptake mechanisms in the current generation of climate models.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE; USDOE Office of Science (SC)
• Grant/Contract Number: AC02-05CH11231; AC05-76RL01830
• OSTI ID: 1845180
• Report Number(s): PNNL-SA-164262; e2021JD035487
• Journal Information: Journal of Geophysical Research: Atmospheres, Journal Name: Journal of Geophysical Research: Atmospheres Journal Issue: 4 Vol. 127; ISSN 2169-897X
• Publisher: American Geophysical Union (AGU)Copyright Statement
• Country of Publication: United States
• Language: English