the global climate system in general, and the regional climate in particular.
AcknowledgementsThe authors are grateful to Laurent Terray at CERFACS, Toulouse, for the initial set-up of the OASIS coupler in Bergen, to Michel De´que´ and David Salas Me´lia, Meteo-France, Toulouse, for providing technical assistance and support, and to Lennart Bengtsson, MPI, Hamburg, for a series of useful discussions and thorough guidance during the work. Constructive criticisms and suggestions made by Ronald J. Stouffer, GFDL, Princeton, during the review process, are greatly appreciated. The development of the Bergen Climate Model and the model inte-grations have received support from the Research Council of
Norway through the RegClim project, the ‘‘Spissforskningsmidler’’
(MB), and the Programme for Supercomputing. Additional funding has been received from the Board of Marine Sciences, University of Bergen, and the European Commission funded project PREDI-CATE (EVK2-CT-1999-00020) (HD). This is contribution A0013 from the Bjerknes Centre for Climate Research.
Appendix 1
1.1 Computation of sea-ice surface temperature
The thermodynamic component of the sea-ice model has one ice layer and one snow layer. The temperature is determined at the ice-snow and the snow-air boundaries, assuming linear temperature profiles in the interior of the ice and snow, and with the freezing temperature of sea water as a boundary condition at the bottom of the ice. The temperatures are then diagnosed by balancing the heat flux budget at the snow-air boundary.
If only the situation with ice and no snow is considered, the heat balance at the top of ice can be stated as:
k@T where k is ice conductivity, T is temperature in the ice, hice is ice thickness,Qnsis non-solar heat flux, andQswis solar heat flux.
The non-solar heat flux depends on the surface temperatureTsand is updated in the atmosphere model using the temperature of the previous time step
Qnns¼QnsðTsn1Þ : ð4Þ
Herendenotes the coupling time step. Assuming a linear temper-ature profile through the ice gives
kTsTf hice
þQnsþQsw¼0 ; ð5Þ whereTfis the freezing temperature of sea water. Solving forTsn+1
using heat fluxes from time stepnleads to an unstable time step procedure. To remedy this, Qns can be linearised around Ts to approximate the non-solar flux atn+ 1:
Q~
Qnþ1ns Qnnsþ@nsn
@Ts
ðTsnþ1TsnÞ : ð6Þ A stable updating ofTsis obtained from
kTsnþ1Tf
hice þQQ~nþ1ns þQnsw¼0 ; ð7Þ The term¶Qnsn/¶Ts, delivered from the atmosphere model, is also used by the coupler to modify the distribution of non-solar heat fluxes received by ocean cells covered by the same atmosphere cell (see Sect. 3).
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