Regionality and seasonality of submesoscale and mesoscale turbulence in the North Pacific Ocean

Type Article
Date 2017-09
Language English
Author(s) Sasaki Hideharu1, Klein Patrice2, Sasai Yoshikazu3, Qiu Bo4
Affiliation(s) 1 : JAMSTEC, Applicat Lab, Kanazawa Ku, 3173-25 Showa Machi, Yokohama, Kanagawa 2360001, Japan.
2 : IFREMER CNRS UBO IRD, Lab Oceanog Phys & Spatiale, Plouzane, France.
3 : JAMSTEC, Res & Dev Ctr Global Change, Yokohama, Kanagawa, Japan.
4 : Univ Hawaii Manoa, Dept Oceanog, Honolulu, HI 96822 USA.
Meeting Topical Collection on the 48th International Liège Colloquium on Ocean Dynamics, Liège, Belgium, 23-27 May 2016
Source Ocean Dynamics (1616-7341) (Springer Heidelberg), 2017-09 , Vol. 67 , N. 9 , P. 1195-1216
DOI 10.1007/s10236-017-1083-y
WOS© Times Cited 52
Keyword(s) Submesoscale turbulence, Scale interactions, Mixed-layer instability, High-resolution simulations, North Pacific

The kinetic energy (KE) seasonality has been revealed by satellite altimeters in many oceanic regions. Question about the mechanisms that trigger this seasonality is still challenging. We address this question through the comparison of two numerical simulations. The first one, with a 1/10° horizontal grid spacing, 54 vertical levels, represents dynamics of physical scales larger than 50 km. The second one, with a 1/30° grid spacing, 100 vertical levels, takes into account the dynamics of physical scales down to 16 km. Comparison clearly emphasizes in the whole North Pacific Ocean, not only a significant KE increase by a factor up to three, but also the emergence of seasonal variability when the scale range 16–50 km (called submesoscales in this study) is taken into account. But the mechanisms explaining these KE changes display strong regional contrasts. In high KE regions, such the Kuroshio Extension and the western and eastern subtropics, frontal mixed-layer instabilities appear to be the main mechanism for the emergence of submesoscales in winter. Subsequent inverse kinetic energy cascade leads to the KE seasonality of larger scales. In other regions, in particular in subarctic regions, results suggest that the KE seasonality is principally produced by larger-scale instabilities with typical scales of 100 km and not so much by smaller-scale mixed-layer instabilities. Using arguments from geostrophic turbulence, the submesoscale impact in these regions is assumed to strengthen mesoscale eddies that become more coherent and not quickly dissipated, leading to a KE increase.

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