Regionality and seasonality of submesoscale and mesoscale turbulence in the North Pacific Ocean
- 1.2k Downloads
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.
KeywordsSubmesoscale turbulence Scale interactions Mixed-layer instability High-resolution simulations North Pacific
The simulations were performed on the Earth Simulator under support of JAMSTEC. H.S. is supported by CANON Foundation. P.K. acknowledges the support of IFREMER (through the MOU IFREMER-JAMSTEC), CNRS (France), and the Agence Nationale pour la Recherche [Contract ANR-10-LABX-19-01 (LabexMER)]. B.Q. acknowledges Science Team support from NASA’s SWOT mission NNX16AH66G. We appriciate comments from two reviewers, that significantly improved the manuscript.
- Komori N, Takahashi K, Komine K, Motoi T, Zhang X, Sagawa G (2005) Description of sea-ice component of coupled ocean sea-ice model for the earth simulator (oifes). J Earth Simul 4:31–45Google Scholar
- Masumoto Y et al (2004) A fifty-year eddy-resolving simulation of the world ocean: preliminary outcomes of OFES (OGCM for the Earth Simulator). J Earth Simul 1:35–56Google Scholar
- Pacanowski RC, Griffies SM (1999) The MOM 3 manual, GFDL Ocean Group Tech. Rep. 4, 680 pp., NOAA/Geophys Fluid Dyn Lab, PrincetonGoogle Scholar
- Pierrehumbert RT, Held IM, Swanson KL (1994) Spectra of local and non-local two-dimensional turbulence. Chaos 4:1111–1116Google Scholar
- Stone PH (1966) On non-geostrophic baroclinic instability. J Atmos Sci 23:3253–3268Google Scholar
- Vallis GK (2006) Atmospheric and oceanic fluid dynamics. Cambridge University Press, 745 ppGoogle Scholar