Floats and f/H

The sensitivity of oceanic float dispersion to f/H, where H is a spatially filtered representation of the water depth, is examined with floats from the Atlantic and Pacific oceans. The first and second moments of the displacements relative to flH were found and compared to those for zonal and meridional displacements. In all cases, the moments relative to f/H display equal or greater anisotropy than those relative to geographical coordinates, suggesting a preferred tendency for spreading along f/H. In regions where the topography is flat (at the equator, in the interior South Atlantic and in the North Pacific), transport is much greater along than across latitude lines, and the moments relative to f/H are essentially the same. But the results differ where the topography is steep (the North Atlantic and near the western boundary in the Equatorial and South Atlantic), where anisotropic spreading relative to f/H occurs even though the geographical moments are isotropic or meridionally-enhanced. Only in the North Pacific, where the topography is smaller scale and less steep, is the spreading more anisotropic in geographical coordinates. The present method is tested using trajectories from a stochastic model, and correctly shows that no such tendency for spreading along f/H exists. Mean and eddy effects are discussed, but are not believed to be well resolved.