Preprints
https://doi.org/10.5194/acp-2020-1213
https://doi.org/10.5194/acp-2020-1213

  26 Nov 2020

26 Nov 2020

Review status: this preprint is currently under review for the journal ACP.

Summer aerosol measurements over the East Antarctic seasonal ice zone

Jack B. Simmons1, Ruhi S. Humphries2,3, Stephen R. Wilson1, Scott D. Chambers4, Alastair G. Williams4, Alan D. Griffiths4,1, Ian M. McRobert5, Jason P. Ward2, Melita D. Keywood2,3, and Sean Gribben2 Jack B. Simmons et al.
  • 1Centre for Atmospheric Chemistry, School of Earth, Atmospheric and Life Sciences, University of Wollongong, Wollongong NSW 2522, Australia
  • 2Climate Science Centre, CSIRO Oceans and Atmosphere, Aspendale VIC 3195, Australia
  • 3Australian Antarctic Program Partnership, University of Tasmania, Hobart TAS, Australia
  • 4ANSTO, Environmental Research, Locked Bag 2001, Kirrawee DC NSW 2232, Australia
  • 5Engineering and Technology Program, CSIRO National Research Collections Australia, Hobart TAS 7004, Australia

Abstract. Aerosol measurements over the Southern Ocean have been identified as critical to an improved understanding of aerosol-radiation and aerosol-cloud interactions, as there currently exists significant discrepancies between model results and measurements in this region. Previous springtime measurements from the East Antarctic seasonal ice zone revealed a significant increase in aerosol number concentrations when crossing the atmospheric polar front into the Polar cell. A return voyage in summer 2017 made a more extensive range of aerosols measurements, including in particular aerosol number concentrations and submicron size distributions. Again, significantly greater aerosol number concentrations were observed in the Polar cell than in the Ferrel cell. Unlike the previous spring voyage however, the polar front was unable to be identified by a step change in aerosol concentration. A possible explanation is that atmospheric mixing across the polar front occurs to a greater degree in summer, therefore weakening the atmospheric boundary at the front. This atmospheric mixing in summer complicates the determination of the polar front location. These changes, together with the increased source of precursors from phytoplankton emissions, are likely to explain the seasonal differences observed in the magnitude of aerosol populations between the Ferrel and Polar cell. In the present analysis, meteorological variables were used to identify different air-masses and then aerosol measurements were compared based on these identifications. CN3 concentrations measured during wind directions indicative of Polar cell airmasses (median 594 cm−3) were larger than those measured during wind directions indicative of Ferrel cell air (median 265 cm−3). CN3 and CCN concentrations were larger during periods where the absolute humidity was less than 4.3 gH2O/m3, indicative of free tropospheric or Antarctic continental airmasses, compared to other periods of the voyage. These results indicate that a persistently more concentrated aerosol population is present in the Polar cell over the East Antarctic seasonal ice zone, although the observed difference between the two cells may vary seasonally.

Jack B. Simmons et al.

 
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Jack B. Simmons et al.

Jack B. Simmons et al.

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Short summary
Aerosols have a climate forcing effect in the earth's atmosphere. Few measurements exist of aerosols in the Southern Ocean, a region key to our understanding of this effect. In this study, aerosol measurements from a summer 2017 campaign in the East Antarctic seasonal ice zone are examined. Higher concentrations of aerosols were found closer in dry air with origins from the Antarctic continent compared to other periods of the voyage.
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