Figure 6: Contours of upper layer depth in February in year 6-9 after initial spin-up. The model is a 2.5 layer hydrodynamic model of the Pacific Ocean from 40°S-40°N. Horizontal resolution is 1/4°× 1/4°. Contour interval is 15m.
PACIFIC OCEAN MODEL
A number of TOMS configurations have been applied to flows in the Pacific Ocean. The two models presented here covers the area from 40°S to 40°N and have a horizontal resolution of 1/4°. Wind forcing for these model runs is monthly mean wind stress from the ECMWF climatology. The simplest model shown is a 2.5 layer model with constant density layers. Initial layer thicknesses for layer 1 and 2 are 200m and 400m, while the density anomalies are 23.6, 26.7 and 27.6. This model was integrated for 9 years with the a repeated wind stress cycle. Figure 6 shows the upper layer thickness anomaly, which is closely related to streamlines for geostrophic currents. It is seen that the solution has significant interannual variability even if the forcing is periodic.
Year 8 has the largest eddy transports, in particular in the Shinkoku Eddy, which is a feature that is present most of the time in these simulations. The flow in layer 1 and 2 is similar in the Kuroshio region, so the 1. baroclinic mode dominates the model solution in that area.
The second version of the model has 4 active layers (i.e. a 4.5 layer model) with the same average upper layer thicknesses given for the Indian Ocean model above. However, it is initialized with variable temperature, salinity and upper layer thickness in order to limit the density variations within each layer. Annual mean values for temperature (Levitus and Boyer, 1994) and salinity (Levitus et al., 1994) were used. The velocity field is initialized to the geostrophic velocity with the bottom of the active layers as reference level. Within 5° of the equator, the value of the Coriolis force at 5° isused. On the equator this results in a discontinuity in the velocity field, but it adjusts quickly due to the fast equatorial wave dynamics. The model is forced with the same ECMWF wind stress as the 2.5 Iayer model, but in addition, Iayer 1 temperature and salinity are restored toward surface Levitus annual mean values.
