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Influences of Recent Particle Formation on Southern Ocean Aerosol Variability and Low Cloud Properties
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  • Isabel L. McCoy,
  • Christopher S. Bretherton,
  • Robert Wood,
  • Cynthia H. Twohy,
  • Andrew Gettelman,
  • Charles Bardeen,
  • Darin W. Toohey,
  • Isabel L. McCoy
Isabel L. McCoy
University of Washington

Corresponding Author:[email protected]

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Christopher S. Bretherton
University of Washington, University of Washington
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Robert Wood
University of Washington, University of Washington
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Cynthia H. Twohy
Northwest Research Associates, Northwest Research Associates
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Andrew Gettelman
National Center for Atmospheric Research (UCAR), National Center for Atmospheric Research (UCAR)
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Charles Bardeen
National Center for Atmospheric Research (UCAR), National Center for Atmospheric Research (UCAR)
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Darin W. Toohey
University of Colorado Boulder, University of Colorado Boulder
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Isabel L. McCoy
University of Washington

Corresponding Author:[email protected]

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Abstract

Controls on pristine aerosol over the Southern Ocean (SO) are critical for constraining the strength of global aerosol indirect forcing. Observations of summertime SO clouds and aerosols in synoptically varied conditions during the 2018 SOCRATES aircraft campaign reveal novel mechanisms influencing pristine aerosol-cloud interactions. The SO free troposphere (3-6 km) is characterized by widespread, frequent new particle formation events contributing to much larger concentrations (≥ 1000 mg-1) of condensation nuclei (diameters > 0.01 μm) than in typical sub-tropical regions. Synoptic-scale uplift in warm conveyor belts and sub-polar vortices lifts marine biogenic sulfur-containing gases to free-tropospheric environments favorable for generating Aitken-mode aerosol particles (0.01-0.1 μm). Free-tropospheric Aitken particles subside into the boundary layer, where they grow in size to dominate the sulfur-based cloud condensation nuclei (CCN) driving SO cloud droplet number concentrations (Nd ~ 60-100 cm-3). Evidence is presented for a hypothesized Aitken-buffering mechanism which maintains persistently high summertime SO Nd against precipitation removal through CCN replenishment from activation and growth of boundary layer Aitken particles. Nudged hindcasts from the Community Atmosphere Model (CAM6) are found to underpredict Aitken and accumulation mode aerosols and Nd, impacting summertime cloud brightness and aerosol-cloud interactions and indicating incomplete representations of aerosol mechanisms associated with ocean biology.
27 Apr 2021Published in Journal of Geophysical Research: Atmospheres volume 126 issue 8. 10.1029/2020JD033529