Frequency dependence of ocean kinetic energy and respective changes over the period 1983–2018

Regional horizontal and vertical patterns of ocean kinetic energy (KE) during 1983-2018 are studied using a numerical simulation. The analysis is focused on time-mean and transient components of KE. For understanding its contribution to the total as function of timescale, the transient part is further sub-divided into six frequency bands, with periods >16 months, 16-8 months, 8-4 months, 4-1 months, 1 month-5 days and <5 days. Near the surface, besides intensification due to wind-forced generation, transient KE is enhanced in boundary currents, in equatorial wave guides and in the Southern Ocean. In the deep, KE is enhanced in re-circulation regions under boundary currents and at eastern sides of topographic ridges. On scales <5 days it is enhanced over shelf and in quiet ocean interior areas. The largest fraction of transient energy resides in the eddy-populated band 1 week-4 months. Decadal changes of KE are associated with mean flow variations and changes on inter- and intra-annual periods, especially in the Atlantic and Southern Oceans. Changes in the subpolar Atlantic are correlated with the North Atlantic Oscillation and in the Southern Ocean with the Southern Annular Mode. A decrease/increase in Atlantic/Pacific KE is noticed over the investigated period. Trends are found in the Gulf Stream, Kuroshio Current and along the Antarctic Circumpolar Current, which shows an increase in mean and transient energy in the Indian/west Pacific sectors and a decrease in the Atlantic sector. The strong variations between decades suggest that trends are part of multi-decadal variability.