The global distribution of f/H and the barotropic response of the ocean

The barotropic response of the ocean over smoothly varying topography is directly related to the potential vorticity gradient ∇f/H. A global estimate of f/H and ∇f/H have been constructed from a high‐resolution digital topographic data base. Four different regimes of the barotropic response of the ocean are suggested by these maps: (1) In the tropical latitudes from 20°S to 20°N, ∇f/H ∼ β/H. The response will be similar to a flat‐bottom Sverdrup regime. (2) In mid‐latitudes (20° to 70°) north of 30°S, ∇f/H ≫ β/H. The response will be quasi‐stationary, weak, and dominated by nonlocal forcing (flow along isolines of f/H). (3) In a number of small regions throughout the mid‐latitudes in both hemispheres, ∇f/H ≪ β/H. In these regions the local response (flow across isolines of f/H) should be amplified, and wavelike motions may occur over a broader bandwidth of frequencies. (4) South of 30°S, the mid‐ocean ridge system becomes zonal and isolates several large regions within closed lines of f/H. In these regions, principally the abyssal plains of the southern ocean, the low‐frequency barotropic response of the ocean may be wavelike in character and much stronger than the Sverdrup response. Consequently, this analysis suggests that the southern ocean may have a stronger barotropic response to wind forcing than the other five major ocean basins.