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Published July 17, 2020 | Published
Journal Article Open

Interannual to Decadal Variations of Submesoscale Motions around the North Pacific Subtropical Countercurrent


The outputs from a submesoscale permitting hindcast simulation from 1990 to 2016 are used to investigate the interannual to decadal variations of submesoscale motions. The region we focus on is the subtropical Northwestern Pacific including the subtropical countercurrent. The submesoscale kinetic energy (KE) is characterized by strong interannual and decadal variability, displaying larger magnitudes in 1996, 2003, and 2015, and smaller magnitudes in 1999, 2009, 2010, and 2016. These variations are partially explained by those of the available potential energy (APE) release at submesoscale driven by mixed layer instability in winter. Indeed, this APE release depends on the mixed layer depth and horizontal buoyancy gradient, both of them modulated with the Pacific Decadal Oscillation (PDO). As a result of the inverse KE cascade, the submesoscale KE variability possibly leads to interannual to decadal variations of the mesoscale KE (eddy KE (EKE)). These results show that submesoscale motions are a possible pathway to explain the impact associated with the PDO on the decadal EKE variability. The winter APE release estimated from the Argo float observations varies synchronously with that in the simulation on the interannual time scales, which suggests the observation capability to diagnose the submesoscale KE variability.

Additional Information

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Received: 29 April 2020; Accepted: 14 July 2020; Published: 17 July 2020. OFES2_NP30 was conducted by using the Earth Simulator under the support of JAMSTEC. B.Q. acknowledges the support from NASA grant NNX17AH33G. Author Contributions: Conceptualization, H.S.; methodology, H.S., B.Q., and P.K.; formal analysis, H.S., B.Q., and P.K.; investigation, H.S.; resources, H.S. and M.N.; data curation, H.S.; writing—original draft preparation, H.S.; writing—review and editing, B.Q., P.K., Y.S., and M.N.; visualization, H.S.; supervision, M.N.; project administration, M.N.; funding acquisition, M.N. All authors have read and agreed to the published version of the manuscript. This research was funded by JSPS of Japan, Grant-in-Aid for Scientific Research on Innovative Areas 6102 (KAKENHI grant number JP19H05701). The authors declare no conflict of interest.

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