Evidence for Secondary Ice Production in Southern Ocean Maritime Boundary Layer Clouds

• Published in: Journal of Geophysical Research: Atmospheres
• Main Authors: Järvinen, Emma, McCluskey, Christina S., Waitz, Fritz, Schnaiter, Martin, Bansemer, Aaron, Bardeen, Charles G., Gettelman, Andrew, Heymsfield, Andrew, Stith, Jeffrey L., Wu, Wei, D’Alessandro, John J., McFarquhar, Greg M., Diao, Minghui, Finlon, Joseph A., Hill, Thomas C. J., Levin, Ezra J. T., Moore, Kathryn A., DeMott, Paul J., McCluskey, Christina S.; 1 National Center for Atmospheric Research Boulder CO USA, Waitz, Fritz; 3 Karlsruhe Institute of Technology Karlsruhe Germany, Schnaiter, Martin; 3 Karlsruhe Institute of Technology Karlsruhe Germany, Bansemer, Aaron; 1 National Center for Atmospheric Research Boulder CO USA, Bardeen, Charles G.; 1 National Center for Atmospheric Research Boulder CO USA, Gettelman, Andrew; 1 National Center for Atmospheric Research Boulder CO USA, Heymsfield, Andrew; 1 National Center for Atmospheric Research Boulder CO USA, Stith, Jeffrey L.; 1 National Center for Atmospheric Research Boulder CO USA, Wu, Wei; 5 Cooperative Institute for Severe and High Impact Weather Research and Operations University of Oklahoma Norman OK USA, D’Alessandro, John J.; 5 Cooperative Institute for Severe and High Impact Weather Research and Operations University of Oklahoma Norman OK USA, McFarquhar, Greg M.; 5 Cooperative Institute for Severe and High Impact Weather Research and Operations University of Oklahoma Norman OK USA, Diao, Minghui; 7 Department of Meteorology and Climate Science San Jose State University San Jose CA USA, Finlon, Joseph A.; 8 Department of Atmospheric Sciences University of Washington Seattle WA USA, Hill, Thomas C. J.; 9 Department of Atmospheric Science Colorado State University Fort Collins CO USA, Levin, Ezra J. T.; 9 Department of Atmospheric Science Colorado State University Fort Collins CO USA, Moore, Kathryn A.; 9 Department of Atmospheric Science Colorado State University Fort Collins CO USA, DeMott, Paul J.; 9 Department of Atmospheric Science Colorado State University Fort Collins CO USA
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2022
• Subjects: ddc:551; southern ocean; mixed‐phase clouds; in‐situ observations; ice crystals; secondary ice; ice nucleating particles; Southern Ocean; Hallett; Rime
• Online Access: https://doi.org/10.1029/2021JD036411; http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/10448

Maritime boundary‐layer clouds over the Southern Ocean (SO) have a large shortwave radiative effect. Yet, climate models have difficulties in representing these clouds and, especially, their phase in this observationally sparse region. This study aims to increase the knowledge of SO cloud phase by presenting in‐situ cloud microphysical observations from the Southern Ocean Clouds, Radiation, Aerosol, Transport Experimental Study (SOCRATES). We investigate the occurrence of ice in summertime marine stratocumulus and cumulus clouds in the temperature range between 6 and −25°C. Our observations show that in ice‐containing clouds, maximum ice number concentrations of up to several hundreds per liter were found. The observed ice crystal concentrations were on average one to two orders of magnitude higher than the simultaneously measured ice nucleating particle (INP) concentrations in the temperature range below −10°C and up to five orders of magnitude higher than estimated INP concentrations in the temperature range above −10°C. These results highlight the importance of secondary ice production (SIP) in SO summertime marine boundary‐layer clouds. Evidence for rime splintering was found in the Hallett‐Mossop (HM) temperature range but the exact SIP mechanism active at lower temperatures remains unclear. Finally, instrument simulators were used to assess simulated co‐located cloud ice concentrations and the role of modeled HM rime‐splintering. We found that CAM6 is deficient in simulating number concentrations across the HM temperature range with little sensitivity to the model HM process, which is inconsistent with the aforementioned observational evidence of highly active SIP processes in SO low‐level clouds. Plain Language Summary: Clouds in the Southern Ocean are important for climate but not well represented in climate models. Observations in this remote region have been rare. This study presents results from a recent airborne campaign that took place in the Southern Ocean where low‐ and mid‐level clouds were ...