Regional Patterns of Ocean Kinetic Energy and its Change During 1980-2018

The ocean kinetic energy is studied using output from two multi-decadal (1980-2018) NCAR Community Earth System Model (CESM) simulations forced by the COREv2 and JRA55 inter-annual forcing fields. The focus of the analysis is put on examining the horizontal and vertical regional patterns of ocean kinetic energy and on decomposing the kinetic energy into time mean, inter-annual and intra-annual components. The latter is further split into five bands, with periods 1) longer than 6 months, 2) between 6 and 3 months, 3) between 3 and 1 month, 4) between 1 month and 5 days and 5) shorter than 5 days. In order to study temporal variations of all kinetic energy compartments, the analysis is not only carried out for the full time period but also for the four different decades individually. Besides the expected exponential decrease with depth from the surface, the transient part of kinetic energy is profoundly enhanced at the eastern sides of topographic ridges. In a top-to-bottom integrated perspective, the largest contribution to the transient kinetic energy comes from the non-seasonal, mostly eddy-driven activity with periods between 3 months and 1 month. Between 1 month and about 1 week, the same oceanic regions are enhanced. High-frequency variability (> 5 day^-1) is enhanced over shelf areas and in the interior of ocean basins away from boundary currents. Results further show a significant temporal change in the partitioning of energy, with enhanced intra-annual energy being identified during the 2000s, together with a corresponding reduction of inter-annual energy. The processes underlying the overall distribution of transient kinetic energy are addressed and finally the possible reasons for the temporal changes are given.