Kinetic energy transfers between mesoscale and submesoscale motions in the open ocean’s upper layers

Mesoscale eddies contain the bulk of the ocean’s kinetic energy (KE), but fundamental questions remain on the cross-scale KE transfers linking eddy generation and dissipation. The role of submesoscale flows represents the key point of discussion, with contrasting views of submesoscales as either a source or a sink of mesoscale KE. Here, the first observational assessment of the annual cycle of the KE transfer between mesoscale and submesoscale motions is per-formed in the upper layers of a typical open-ocean region. Although these diagnostics have marginal statistical significance and should be regarded cautiously, they are physically plausible and can provide a valuable benchmark for model evalua-tion. The cross-scale KE transfer exhibits two distinct stages, whereby submesoscales energize mesoscales in winter and drain mesoscales in spring. Despite this seasonal reversal, an inverse KE cascade operates throughout the year across much of the mesoscale range. Our results are not incompatible with recent modeling investigations that place the head-waters of the inverse KE cascade at the submesoscale, and that rationalize the seasonality of mesoscale KE as an inverse cascade-mediated response to the generation of submesoscales in winter. However, our findings may challenge those investigations by suggesting that, in spring, a downscale KE transfer could dampen the inverse KE cascade. An exploratory appraisal of the dynamics governing mesoscale–submesoscale KE exchanges suggests that the upscale KE transfer in winter is underpinned by mixed layer baroclinic instabilities, and that the downscale KE transfer in spring is associated with frontogenesis. Current submesoscale-permitting ocean models may substantially understate this downscale KE transfer, due to the models’ muted representation of frontogenesis.

Ageostrophic circulations, Dynamics, Eddies, Energy transport, Frontogenesis/frontolysis, Instability, Mesoscale processes, Nonlinear dynamics, Ocean circulation, Ocean dynamics, Small scale processes, Turbulence

10.1175/JPO-D-21-0099.1

0022-3670

75-97

Naveira Garabato, Alberto

97c0e923-f076-4b38-b89b-938e11cea7a6

Yu, X.

d30b09cd-8454-4f27-8590-4d3ee0f19e9f

Callies, Jörn

d7d71837-daff-4e61-955c-1f8e50bd3d67

Barkan, Roy

65fbf32e-8e93-4d02-bbba-1c18f39657e8

Polzin, Kurt L.

2424c950-d9b0-471c-95c0-b7b9d44132a1

Frajka-Williams, Eleanor

da86044e-0f68-4cc9-8f60-7fdbc4dc19cb

Buckingham, Christian E

dba7c776-a8c6-4617-ad40-7919dd4ab3dc

Griffies, Stephen M.

bcc53ed0-1893-46cf-ac21-56259f8722f6

1 January 2022

Naveira Garabato, Alberto

97c0e923-f076-4b38-b89b-938e11cea7a6

Yu, X.

d30b09cd-8454-4f27-8590-4d3ee0f19e9f

Callies, Jörn

d7d71837-daff-4e61-955c-1f8e50bd3d67

Barkan, Roy

65fbf32e-8e93-4d02-bbba-1c18f39657e8

Polzin, Kurt L.

2424c950-d9b0-471c-95c0-b7b9d44132a1

Frajka-Williams, Eleanor

da86044e-0f68-4cc9-8f60-7fdbc4dc19cb

Buckingham, Christian E

dba7c776-a8c6-4617-ad40-7919dd4ab3dc

Griffies, Stephen M.

bcc53ed0-1893-46cf-ac21-56259f8722f6

Naveira Garabato, Alberto, Yu, X., Callies, Jörn, Barkan, Roy, Polzin, Kurt L., Frajka-Williams, Eleanor, Buckingham, Christian E and Griffies, Stephen M. (2022) Kinetic energy transfers between mesoscale and submesoscale motions in the open ocean’s upper layers. Journal of Physical Oceanography, 52 (1), 75-97. (doi:10.1175/JPO-D-21-0099.1).

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Kinetic Energy Transfers between Mesoscale and Submesoscale Motions in the Open Ocean’s Upper Layers - Accepted Manuscript

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[15200485 - Journal of Physical Oceanography] Kinetic Energy Transfers between Mesoscale and Submesoscale Motions in the Open Ocean’s Upper Layers - Version of Record

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Accepted/In Press date: 21 September 2021

Published date: 1 January 2022

Additional Information: Funding Information: Acknowledgments. The OSMOSIS experiment was funded by the U.K. Natural Environment Research Council (NERC) through Grants NE/1019999/1 and NE/101993X/1. ACNG acknowledges the support of the Royal Society and the Wolfson Foundation, and XY that of a China Scholarship Council PhD studentship. We are grateful to the engineers, scientists, captain, and crew of the RRS Discovery, RRS James Cook, and R/V Celtic Explorer, who participated in the deployment and recovery of the moorings and gliders. All data are archived at the British Oceanographic Data Centre. We thank Zachary Erickson and Andrew Thompson for providing us with the LLC4320 model output, and Baylor Fox-Kemper, Hemant Khatri and three anonymous reviewers for insightful feedback. Funding Information: The OSMOSIS experiment was funded by the U.K. Natural Environment Research Council (NERC) through Grants NE/1019999/1 and NE/101993X/1. ACNG acknowledges the support of the Royal Society and the Wolfson Foundation, and XY that of a China Scholarship Council PhD studentship. We are grateful to the engineers, scientists, captain, and crew of the RRS Discovery, RRS James Cook, and R/V Celtic Explorer, who participated in the deployment and recovery of the moorings and gliders. All data are archived at the British Oceanographic Data Centre. We thank Zachary Erickson and Andrew Thompson for providing us with the LLC4320 model out-put, and Baylor Fox-Kemper, Hemant Khatri and three anonymous reviewers for insightful feedback. Publisher Copyright: © 2022 American Meteorological Society. Copyright: Copyright 2022 Elsevier B.V., All rights reserved.

Keywords: Ageostrophic circulations, Dynamics, Eddies, Energy transport, Frontogenesis/frontolysis, Instability, Mesoscale processes, Nonlinear dynamics, Ocean circulation, Ocean dynamics, Small scale processes, Turbulence