A few hundred current meter records of roughly one to two years' duration are now available from diverse locations in the world's oceans, primarily the North Atlantic. The shape of the spectrum for low-frequency ocean current fluctuations is shown to have a geographical distribution related to the general circulation. In the offshore segment of the Gulf Stream and Kuroshio Extension systems along with their recirculations, and near the Agulhas Current as well, normalized frequency distributions of eddy kinetic energy tend to be comparatively depth-independent and peaked at the mesoscale. However, in the immediate vicinity of current axes or fronts, spectral shapes may become “red” in the thermocline, as a result of low-frequency meandering of a baroclinic jet across mooring sites. Normalized frequency distributions of eddy kinetic energy from some areas distant from strong currents but perhaps near weaker upper-ocean fronts tend to be baroclinic and not peaked at the mesoscale in the thermocline, rather they are “red” there, although peaked at the mesoscale at abyssal depths. There are also low energy regions where spectral shapes tend to be red and comparatively independent of depth. In some areas, frequency distributions are relatively energetic or peaked at periods of order days, normally at depth near bottom relief.
Schmitz, William J., and James R. Luyten. 1991. "Spectral time scales for mid-latitude eddies." Journal of Marine Research 49, (1). https://elischolar.library.yale.edu/journal_of_marine_research/1994