Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
doi:10.5194/acp-2017-212
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
21 Apr 2017
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
In situ measurements of cloud microphysics and aerosol over coastal Antarctica during the MAC campaign
Sebastian J. O'Shea1, Thomas W. Choularton1, Michael Flynn1, Keith N. Bower1, Martin Gallagher1, Jonathan Crosier1,2, Ian Crawford3, Zoë Fleming4, Constantino Listowski4,a, Amélie Kirchgaessner4, Russel S. Ladkin4, and Thomas Lachlan-Cope4 1School of Earth and Environmental Sciences, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
2National Centre for Atmospheric Science, University of Manchester, Oxford Road, Manchester, M13 9PL, UK
3National Centre for Atmospheric Science, Department of Chemistry, University of Leicester, Leicester, LE1 7RH, UK
4British Antarctic Survey, NERC, High Cross, Madingley Rd, Cambridge CB3 0ET, UK
anow at: LATMOS/IPSL, UVSQ Université Paris-Saclay, UPMC Univ. Paris 06, CNRS, Guyancourt, France
Abstract. During austral summer 2015 the Microphysics of Antarctic Clouds (MAC) field campaign collected detailed airborne and ground based in situ measurements of cloud and aerosol properties over coastal Antarctica and the Weddell Sea. This paper presents the first results from the experiment and discusses the key processes important in this region.

The sampling was predominantly of stratus cloud, at temperatures between −20 and 0 °C. These clouds were dominated by supercooled liquid water droplets, which had a median concentration of 113 cm−3 and an inter-quartile range of 86 cm−3. The concentration of large aerosols (0.5 to 1.6 μm) decreased with altitude and were depleted in airmasses that originated over the Antarctic Continent compared to those more heavily influenced by the Southern Ocean and sea ice regions. The dominant aerosol in the region was hygroscopic in nature, with the hygroscopicity parameter, κ having a median value for the campaign of 0.64 (interquartile range = 0.34). This is consistent with other remote marine locations that are dominated by sea salt/sulphate.

Cloud ice particle concentrations were highly variable with the ice tending to occur in small isolated patches. Below ca 2000 m glaciated cloud regions were more common at higher temperatures; however the clouds were still predominantly liquid throughout. When ice was present at temperatures higher than −10 °C, secondary ice production most likely through the Hallet-Mossop mechanism lead to ice concentrations 1 to 3 orders of magnitude higher than the number predicted by commonly used primary ice nucleation parameterisations. The drivers of the ice crystal variability are investigated. No clear dependence on the droplet size distribution was found. However, higher ice concentrations were found in updrafts and downdrafts compared to quiescent regions. The source of first ice in the clouds remains uncertain, but may include contributions from biogenic particles, blowing snow or other surface ice production mechanisms.


Citation: O'Shea, S. J., Choularton, T. W., Flynn, M., Bower, K. N., Gallagher, M., Crosier, J., Crawford, I., Fleming, Z., Listowski, C., Kirchgaessner, A., Ladkin, R. S., and Lachlan-Cope, T.: In situ measurements of cloud microphysics and aerosol over coastal Antarctica during the MAC campaign, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-212, in review, 2017.
Sebastian J. O'Shea et al.
Sebastian J. O'Shea et al.
Sebastian J. O'Shea et al.

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Short summary
Few direct measurements have been made of Antarctic cloud and aerosol properties. As part of the 2015 Microphysics of Antarctic Clouds (MAC) field campaign detailed airborne and ground based measurements were made over the Weddell Sea and Antarctic coastal continent. This paper presents the first results from this campaign and discusses the cloud properties and processes important in this region.
Few direct measurements have been made of Antarctic cloud and aerosol properties. As part of the...
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