Ocean configuration

Ocean grid and bathymetry

The CM2Mc ocean uses a tripolar grid (Murray, 1996) to avoid the singularity at the north pole. The horizontal dimensions of the ocean grid vary according to latitude, with enhanced latitudinal resolution near the equator and at midlatitudes. The horizontal area per cell also varies due to the decreasing distance between lines of longitude at higher latitude. As a result, the effective resolution, in 'nominal degree units' (i.e. the square root of cell area, in degrees latitude) averages 2.7 degrees, with finest resolution of 1.01 at the equator and coarsest of 3.39 degrees in the subtropics. The minimum latitudinal resolution at the equator is 0.6 degrees, allowing an explicit physical representation of the equatorial currents. There are 28 vertical levels, the uppermost eight of which are each 10 m thick, below which the layers gradually increase in thickness to a maximum of 506 m. The model employs partial bottom cells (Adcroft et al., 1997; Pacanowski and Gnanadesikan, 1998) to allow a more realistic representation of the bathymetry, with a maximum depth of 5500 m. The bathymetry was initially generated from interpolation of satellite bathymetry, and heavily smoothed. The result was then carefully examined, and critical features destroyed in the coarse interpolation and smoothing were manually restored. In particular, these include the Bering Strait, passages within the Canadian archipelago, the Aleutian Islands,the Sea of Okhotsk, the Denmark Strait, the Iceland-Scotland ridge, Japan, Indonesia, deep

Indo-Pacific fracture zones, and the Princess Elizabeth Trough. These changes were made in order to improve the representation of the bathymetry, rather than in order to improve the simulation, with the exception of the region of the Indonesian Throughflow, which was readjusted twice in order to produce a reasonable throughflow under the control climate simulation, and the Aleutian Islands, which were adjusted iteratively in order to provide a realistic separation between the Bering Sea and open Pacific subarctic gyre. In order to compensate for mixing between water masses where the coarse resolution of the topography does not allow dynamical mixing, the cross-land mixing scheme of Griffies (ref) is employed. This generates less than 2 Sv of total mixing at each of: strait of Gibraltar, the straits of Bosphorus, the entrance of the Baltic Sea, the Boothia-Fox peninsula, the Unimak passage, and between the Japan Sea and the open Pacific.