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Volume 16, issue 3 | Copyright

Special issue: Aerosol-Cloud Coupling And Climate Interactions in the Arctic...

Atmos. Chem. Phys., 16, 1545-1563, 2016
https://doi.org/10.5194/acp-16-1545-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 10 Feb 2016

Research article | 10 Feb 2016

Observations of surface momentum exchange over the marginal ice zone and recommendations for its parametrisation

A. D. Elvidge1,a, I. A. Renfrew1, A. I. Weiss2, I. M. Brooks3, T. A. Lachlan-Cope2, and J. C. King2 A. D. Elvidge et al.
  • 1School of Environmental Sciences, University of East Anglia, Norwich, UK
  • 2British Antarctic Survey, Cambridge, UK
  • 3School of Earth and Environment, University of Leeds, Leeds, UK
  • apresent address: Atmospheric Processes and Parametrisations, Met Office, Fitzroy Road, Exeter, UK

Abstract. Comprehensive aircraft observations are used to characterise surface roughness over the Arctic marginal ice zone (MIZ) and consequently make recommendations for the parametrisation of surface momentum exchange in the MIZ. These observations were gathered in the Barents Sea and Fram Strait from two aircraft as part of the Aerosol–Cloud Coupling And Climate Interactions in the Arctic (ACCACIA) project. They represent a doubling of the total number of such aircraft observations currently available over the Arctic MIZ. The eddy covariance method is used to derive estimates of the 10m neutral drag coefficient (CDN10) from turbulent wind velocity measurements, and a novel method using albedo and surface temperature is employed to derive ice fraction. Peak surface roughness is found at ice fractions in the range 0.6 to 0.8 (with a mean interquartile range in CDN10 of 1.25 to 2.85 × 10−3). CDN10 as a function of ice fraction is found to be well approximated by the negatively skewed distribution provided by a leading parametrisation scheme (Lüpkes et al., 2012) tailored for sea-ice drag over the MIZ in which the two constituent components of drag – skin and form drag – are separately quantified. Current parametrisation schemes used in the weather and climate models are compared with our results and the majority are found to be physically unjustified and unrepresentative. The Lüpkes et al. (2012) scheme is recommended in a computationally simple form, with adjusted parameter settings. A good agreement holds for subsets of the data from different locations, despite differences in sea-ice conditions. Ice conditions in the Barents Sea, characterised by small, unconsolidated ice floes, are found to be associated with higher CDN10 values – especially at the higher ice fractions – than those of Fram Strait, where typically larger, smoother floes are observed. Consequently, the important influence of sea-ice morphology and floe size on surface roughness is recognised, and improvement in the representation of this in parametrisation schemes is suggested for future study.

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Rare aircraft observations of surface momentum flux over the Arctic marginal ice zone provide the best means yet to constrain model representation of MIZ surface roughness. The sensitivity of surface roughness to ice concentration over the Arctic MIZ is presented; these results do not support the values used in many models. However, a leading parameterization scheme (that of Lüpkes et al., 2012) is found to provide a good representation of form drag, after some parameter alterations.
Rare aircraft observations of surface momentum flux over the Arctic marginal ice zone provide...
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