Abstract
Ocean eddies (with a size of 100–300 km), ubiquitous in satellite observations, are known to represent about 80% of the total ocean kinetic energy. Recent studies have pointed out the unexpected role of smaller oceanic structures (with 1–50 km scales) in generating and sustaining these eddies. The interpretation proposed so far invokes the internal instability resulting from the large-scale interaction between upper and interior oceanic layers. Here we show, using a new high-resolution simulation of the realistic North Pacific Ocean, that ocean eddies are instead sustained by a different process that involves small-scale mixed-layer instabilities set up by large-scale atmospheric forcing in winter. This leads to a seasonal evolution of the eddy kinetic energy in a very large part of this ocean, with an amplitude varying by a factor almost equal to 2. Perspectives in terms of the impacts on climate dynamics and future satellite observational systems are briefly discussed.
Highlights
IntroductionOcean eddies (with a size of 100–300 km), ubiquitous in satellite observations, are known to represent about 80% of the total ocean kinetic energy
Ocean eddies, ubiquitous in satellite observations, are known to represent about 80% of the total ocean kinetic energy
Subsequent investigations of these different regimes in the global ocean[5] have revealed a dominance of the Phillips regime in energetic eastward currents such as the Gulf Stream and the Kuroshio, whereas the Charney regime may dominate in some other parts of the oceans. This questions the validity of the interpretation of observational results in terms of the Charney-like regime in many regions including the energetic eastward currents. We address this question using a new realistic simulation of the North Pacific Ocean at high resolution[18] forced by atmospheric reanalysis data
Summary
Ocean eddies (with a size of 100–300 km), ubiquitous in satellite observations, are known to represent about 80% of the total ocean kinetic energy. The resulting mesoscale turbulent dynamics is referred to as the Phillips regime[5] (after the seminal work of Phillips[6] related to baroclinic instability in the ocean interior) and leads to a velocity spectrum with a k À 3 slope, with k being the wavenumber In this regime, smaller-scale structures (O(1–50 km)), called submesoscales, are very weakly energetic and have little impact on mesoscale eddies, except in terms of KE dissipation. Recent reanalysis of satellite altimeter and in situ data[7,8,9,10] have pointed out that submesoscales are much more energetic than expected in many regions of the oceans, involving a k À 2 spectrum slope over a large range of scales, which suggests an impact of these small scales on larger scales This questioned the paradigm related to the Phillips regime. Results indicate that the impact of the winter MLIs on mesoscale KE clearly overcomes other dynamical regimes: the resulting submesoscale KE feeds larger scales through an efficient inverse KE cascade, leading to a strong seasonal modulation of the eddy KE (in the 100–300 km band)
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