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Volume 9, issue 3 | Copyright
Geosci. Model Dev., 9, 1125-1141, 2016
https://doi.org/10.5194/gmd-9-1125-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Development and technical paper 24 Mar 2016

Development and technical paper | 24 Mar 2016

The location of the thermodynamic atmosphere–ice interface in fully coupled models – a case study using JULES and CICE

Alex E. West, Alison J. McLaren, Helene T. Hewitt, and Martin J. Best Alex E. West et al.
  • Met Office Hadley Centre, Exeter Devon, UK

Abstract. In fully coupled climate models, it is now normal to include a sea ice component with multiple layers, each having their own temperature. When coupling this component to an atmosphere model, it is more common for surface variables to be calculated in the sea ice component of the model, the equivalent of placing an interface immediately above the surface. This study uses a one-dimensional (1-D) version of the Los Alamos sea ice model (CICE) thermodynamic solver and the Met Office atmospheric surface exchange solver (JULES) to compare this method with that of allowing the surface variables to be calculated instead in the atmosphere, the equivalent of placing an interface immediately below the surface.

The model is forced with a sensible heat flux derived from a sinusoidally varying near-surface air temperature. The two coupling methods are tested first with a 1 h coupling frequency, and then a 3 h coupling frequency, both commonly used. With an above-surface interface, the resulting surface temperature and flux cycles contain large phase and amplitude errors, and have a very blocky shape. The simulation of both quantities is greatly improved when the interface is instead placed within the top ice layer, allowing surface variables to be calculated on the shorter timescale of the atmosphere. There is also an unexpected slight improvement in the simulation of the top-layer ice temperature by the ice model. The surface flux improvement remains when a snow layer is added to the ice, and when the wind speed is increased. The study concludes with a discussion of the implications of these results to three-dimensional modelling. An appendix examines the stability of the alternative method of coupling under various physically realistic scenarios.

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This study compares two methods of coupling a sea ice model to an atmospheric model in a series of idealized one-dimensional experiments. The JULES method calculates surface variables in the atmosphere; the CICE method calculates surface variables in the sea ice. It is found that simulations of all variables are more accurate in the JULES method, likely because of the shorter time step of the atmosphere.
This study compares two methods of coupling a sea ice model to an atmospheric model in a series...
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