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Preprints
https://doi.org/10.5194/acp-2019-1081
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-1081
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 27 Nov 2019

Submitted as: research article | 27 Nov 2019

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A revised version of this preprint is currently under review for the journal ACP.

Marine productivity and synoptic meteorology drive summer-time variability in Southern Ocean aerosols

Joel Alroe1, Luke T. Cravigan1, Branka Miljevic1, Graham R. Johnson1, Paul Selleck2, Ruhi S. Humphries2, Melita D. Keywood2, Scott D. Chambers3, Alastair G. Williams3, and Zoran D. Ristovski1 Joel Alroe et al.
  • 1School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane, Australia
  • 2Climate Science Centre, CSIRO Oceans and Atmosphere, Aspendale, Australia
  • 3Environmental Research, ANSTO, Lucas Heights, Australia

Abstract. Cloud-radiation interactions over the Southern Ocean are not well constrained in climate models, in part due to uncertainties in the sources, concentrations and cloud-forming potential of aerosol in this region. To date, most studies in this region have reported measurements from fixed terrestrial stations or a limited set of instrumentation, and often present findings as broad seasonal or latitudinal trends. Here, we present an extensive set of aerosol and meteorological observations obtained during an austral summer cruise across the full width of the Southern Ocean south of Australia. Three episodes of continental-influenced air masses were identified, including an apparent transition between the Ferrel atmospheric cell and the polar cell at approximately 64° S. During the other two episodes, synoptic-scale weather patterns diverted air masses across distances greater than 1000 km from the Australian and Antarctic coastlines, respectively, indicating that a large proportion of the Southern Ocean may be periodically influenced by continental air masses. In all three cases, a highly cloud-active accumulation mode dominated the size distribution, with up to 93 % of the total number concentration activating as cloud condensation nuclei. In contrast, sampling periods influenced by marine air masses frequently demonstrated a correlation between air mass trajectories over regions of high biological productivity and subsequent enhancement of an Aitken mode centred at approximately 30 nm and contributing an average of 71 % of the total aerosol number concentration. Although these small diameters limited their contribution to cloud condensation nuclei concentrations, Aitken number concentrations and diameters were highly variable. A detailed investigation of the marine air masses revealed that this variability may be attributed to the availability of biogenic precursors, the competing influence of condensation sinks (such as sea spray aerosol) and vertical transport between the marine boundary layer and the free troposphere. This variability of the marine Aitken mode as well as the instances of long-range transport were governed by synoptic-scale weather systems, through their influence on air mass trajectories and both generation and depletion of condensation sinks. These results demonstrate the highly dynamic nature of Southern Ocean aerosol and their complex dependence on both biological productivity and synoptic-scale weather systems.

Joel Alroe et al.

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Short summary
We present findings from an austral summer voyage across the full latitudinal width of the Southern Ocean, south of Australia. Aerosol properties were strongly influenced by marine biological activity, synoptic-scale weather systems and long range transport of continental-influenced air masses. These results demonstrate highly variable aerosol sources and characteristics, and highlight the need for further measurements in this region.
We present findings from an austral summer voyage across the full latitudinal width of the...
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