Interpreting Energy and Tracer Spectra of Upper-Ocean Turbulence in the Submesoscale Range (1-200 km)

• Published in: Journal of physical oceanography Vol. 43; no. 11; pp. 2456 - 2474
• Main Authors: CALLIES, Jörn, FERRARI, Raffaele
• Format: Journal Article
• Language: English
• Published: Boston, MA American Meteorological Society 01.11.2013
• Subjects: Baroclinic instability; Earth, ocean, space; Energy; Energy spectra; Exact sciences and technology; External geophysics; Gulf Stream; Internal tides; Kinetic energy; Marine; Meteorology; Mixed layer; Ocean circulation; Ocean currents; Oceanic turbulence; Oceans; Physics of the oceans; Potential energy; Predictions; Rivers; Spectra; Stratification; Surface water; Theories; Theory; Thermocline; Thermohaline structure and circulation. Turbulence and diffusion; Tidal dynamics; Tides; Tracers; Turbulence; Wave energy; Wave power; Wavelengths; North Atlantic; Pacific Ocean; Northeast Pacific; Atlantic Ocean; Gulf Stream; North Pacific; AN, North Atlantic, Gulf Stream; IN, North Pacific; A, Atlantic, Gulf Stream; Quasi geostrophic approximation; ocean currents; Potential energy; Measurement in situ; Energy spectrum; Boundary current; kinetic energy; Mesoscale; Oceanic turbulence; Eastern boundary current; Observation data
• ISSN: 0022-3670; 1520-0485
• DOI: 10.1175/jpo-d-13-063.1

Abstract Submesoscale (1–200 km) wavenumber spectra of kinetic and potential energy and tracer variance are obtained from in situ observations in the Gulf Stream region and in the eastern subtropical North Pacific. In the Gulf Stream region, steep kinetic energy spectra at scales between 200 and 20 km are consistent with predictions of interior quasigeostrophic–turbulence theory, both in the mixed layer and in the thermocline. At scales below 20 km, the spectra flatten out, consistent with a growing contribution of internal-wave energy at small scales. In the subtropical North Pacific, the energy spectra are flatter and inconsistent with predictions of interior quasigeostrophic–turbulence theory. The observed spectra and their dependence on depth are also inconsistent with predictions of surface quasigeostrophic–turbulence theory for the observed ocean stratification. It appears that unbalanced motions, most likely internal tides at large scales and the internal-wave continuum at small scales, dominate the energy spectrum throughout the submesoscale range. Spectra of temperature variance along density surfaces, which are not affected by internal tides, are also inconsistent with predictions of geostrophic-turbulence theories. Reasons for this inconsistency could be the injection of energy in the submesoscale range by small-scale baroclinic instabilities or modifications of the spectra by coupling between surface and interior dynamics or by ageostrophic frontal effects.