EGU2020-8546
https://doi.org/10.5194/egusphere-egu2020-8546
EGU General Assembly 2020
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

A comparison of two alternative approaches to modelling the sea ice floe size distribution.

Adam Bateson1, Daniel Feltham1, David Schröder1, Lucia Hosekova1,2, Jeff Ridley3, and Yevgeny Aksenov4
Adam Bateson et al.
  • 1Department of Meteorology, University of Reading, Reading, United Kingdom of Great Britain and Northern Ireland (a.w.bateson@pgr.reading.ac.uk)
  • 2Applied Physics Laboratory, University of Washington, Seattle, United States of America
  • 3Hadley Centre for Climate Prediction and Research, Met Office, Exeter, United Kingdom of Great Britain and Northern Ireland
  • 4National Oceanography Centre Southampton, Southampton, United Kingdom of Great Britain and Northern Ireland

Sea ice exists as individual units of ice called floes. These floes can vary by orders of magnitude in diameter over small spatial scales. They are better described by a floe size distribution (FSD) rather than by a single diameter. Observations of the FSD are frequently fitted to a power law with a negative exponent. Floe size can influence several sea ice processes including the lateral melt rate, momentum exchange between the sea ice, ocean and atmosphere, and sea ice rheology. There have been several recent efforts to develop a model of the floe size distribution to include within sea ice models to improve the representation of floe size beyond a fixed single value. Some of these involve significant approximations about the shape and variability of the distribution whereas others adopt a more prognostic approach that does not restrict the shape of the distribution.

In this study we compare the impacts of two alternative approaches to modelling the FSD within the CICE sea ice model. The first assumes floes follow a power law distribution with a constant exponent. Parameterisations of processes thought to influence the floe size distribution are expressed in terms of a variable FSD tracer. The second uses a prognostic floe size-thickness distribution. The sea ice area in individual floe size categories evolves independently such that the shape of distribution is an emergent behaviour rather than imposed. Here we compare the impact of the two modelling approaches on the thermodynamic evolution of the sea ice. We show that both predict an increase in lateral melt with a compensating reduction in basal melt. We find that the magnitude of this change is highly dependent on the form of the distribution for the smallest floes. We also explore the impact of both FSD models on the momentum exchange of the sea ice and find a large response in the spatial distribution of sea ice volume. Finally, we will discuss whether the results from the prognostic FSD model support the assumptions required to construct the power law derived FSD model.

How to cite: Bateson, A., Feltham, D., Schröder, D., Hosekova, L., Ridley, J., and Aksenov, Y.: A comparison of two alternative approaches to modelling the sea ice floe size distribution. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8546, https://doi.org/10.5194/egusphere-egu2020-8546, 2020.

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