GYRE family: double gyre basin

The GYRE configuration [Lévy et al., 2010] has been built to simulate the seasonal cycle of a double-gyre box model. It consists in an idealized domain similar to that used in the studies of Drijfhout [1994] and Hazeleger and Drijfhout [2000b], Hazeleger and Drijfhout [1998], Hazeleger and Drijfhout [2000a], Hazeleger and Drijfhout [1999], over which an analytical seasonal forcing is applied. This allows to investigate the spontaneous generation of a large number of interacting, transient mesoscale eddies and their contribution to the large scale circulation.

The domain geometry is a closed rectangular basin on the $\beta$-plane centred at $\sim$ 30and rotated by 45, 3180 km long, 2120 km wide and 4 km deep (Fig. 15.1). The domain is bounded by vertical walls and by a flat bottom. The configuration is meant to represent an idealized North Atlantic or North Pacific basin. The circulation is forced by analytical profiles of wind and buoyancy fluxes. The applied forcings vary seasonally in a sinusoidal manner between winter and summer extrema [Lévy et al., 2010]. The wind stress is zonal and its curl changes sign at 22and 36. It forces a subpolar gyre in the north, a subtropical gyre in the wider part of the domain and a small recirculation gyre in the southern corner. The net heat flux takes the form of a restoring toward a zonal apparent air temperature profile. A portion of the net heat flux which comes from the solar radiation is allowed to penetrate within the water column. The fresh water flux is also prescribed and varies zonally. It is determined such as, at each time step, the basin-integrated flux is zero. The basin is initialised at rest with vertical profiles of temperature and salinity uniformly applied to the whole domain.

The GYRE configuration is set through the &namcfg namelist defined in the reference configuration CONFIG/GYRE/EXP00/namelist_cfg. Its horizontal resolution (and thus the size of the domain) is determined by setting jp_cfg :
jpiglo $= 30 \times$ jp_cfg + 2
jpjglo $= 20 \times$ jp_cfg + 2
Obviously, the namelist parameters have to be adjusted to the chosen resolution, see the Configurations pages on the NEMO web site (Using NEMOConfigurations) . In the vertical, GYRE uses the default 30 ocean levels (jpk=31) (Fig. 4.6).

The GYRE configuration is also used in benchmark test as it is very simple to increase its resolution and as it does not requires any input file. For example, keeping a same model size on each processor while increasing the number of processor used is very easy, even though the physical integrity of the solution can be compromised.

Figure 16.3: Snapshot of relative vorticity at the surface of the model domain in GYRE R9, R27 and R54. From Lévy et al. [2010].