Inferring dynamics from the wavenumber spectra of an eddying global ocean model with embedded tides

Richman, James G.; Arbic, Brian K.; Shriver, Jay F.; Metzger, E. Joseph; Wallcraft, Alan J.

doi:10.1029/2012jc008364

Cited by 97 publications

(149 citation statements)

References 38 publications

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“…One possible explanation is that Xu and Fu's estimates, despite the attempt to remove instrumental noise, are still contaminated by noise at scales that are only marginally resolved by altimeters. This was corroborated by the modeling results of Sasaki and Klein (2012) and Richman et al (2012), who found steeper spectra than the altimetric ones in regions of low mesoscale activity. A second possibility is that ageostrophic flows, like internal tides, have an important signature in SSH, so that velocities inferred from SSH using geostrophic balance are not accurate .…”

Section: Altimetry Observationssupporting

confidence: 77%

“…Using model output provided by Richman et al, we find that internal tides do indeed dominate the kinetic energy at scales of order 100 km in the region under consideration here. Richman et al (2012) also found that the peaks due to internal tides are considerably broadened, which, together with the superposition with subinertial energy, could explain why no distinct peaks are apparent in the observed spectra.…”

Section: Discussionmentioning

confidence: 72%

“…There is instead support for a strong internal-tide field in the region. Richman et al (2012) ran numerical simulations of the global oceans that resolved both geostrophic eddies and low-mode tides. They found that in regions of low mesoscale and high tidal activity, superinertial variability dominates the kinetic energy spectra from scales of a few kilometers to 100 km and larger.…”

Section: Discussionmentioning

confidence: 99%

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Submesoscale turbulence in the upper ocean

Callies¹

2016

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Submesoscale flows, current systems 1-100 km in horizontal extent, are increasingly coming into focus as an important component of upper-ocean dynamics. A range of processes have been proposed to energize submesoscale flows, but which process dominates in reality must be determined observationally. We diagnose from observed flow statistics that in the thermocline the dynamics in the submesoscale range transition from geostrophic turbulence at large scales to inertia-gravity waves at small scales, with the transition scale depending dramatically on geographic location. A similar transition is shown to occur in the atmosphere, suggesting intriguing similarities between atmospheric and oceanic dynamics. We furthermore diagnose from upper-ocean observations a seasonal cycle in submesoscale turbulence: fronts and currents are more energetic in the deep wintertime mixed layer than in the summertime seasonal thermocline. This seasonal cycle hints at the importance of baroclinic mixed layer instabilities in energizing submesoscale turbulence in winter. To better understand this energization, three aspects of the dynamics of baroclinic mixed layer instabilities are investigated. First, we formulate a quasigeostrophic model that describes the linear and nonlinear evolution of these instabilities. The simple model reproduces the observed wintertime distribution of energy across scales and depth, suggesting it captures the essence of how the submesoscale range is energized in winter. Second, we investigate how baroclinic instabilities are affected by convection, which is generated by atmospheric forcing and dominates the mixed layer dynamics at small scales. It is found that baroclinic instabilities are remarkably resilient to the presence of convection and develop even when rapid overturns keep the mixed layer unstratified. Third, we discuss the restratification induced by baroclinic mixed layer instabilities. We show that the rate of restratification depends on characteristics of the baroclinic eddies themselves, a dependence not captured by a previously proposed parameterization. These insights sharpen our understanding of submesoscale dynamics and can help focus future inquiry into whether and how submesoscale flows influence the ocean's role in climate.Thesis supervisor: Raffaele Ferrari Title: Breene M. Kerr Professor of Oceanography

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Section: Altimetry Observationssupporting

confidence: 77%

Section: Discussionmentioning

confidence: 72%

Section: Discussionmentioning

confidence: 99%

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Submesoscale turbulence in the upper ocean

Callies¹

2016

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“…Altimetric observations and high-resolution simulations show that baroclinic tides appear as somewhat broadened peaks in wavenumber spectra, to the extent that they may be better described as broad-band signals (e.g., Ray and Mitchum 1997;Zhao et al 2012;Richman et al 2012). A theory that explains this signature in wavenumber spectra is lacking and in situ observations are difficult because of the tides' large spatial scales and high frequencies.…”

Section: Tidesmentioning

confidence: 99%

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

Callies

Ferrari

2013

Journal of Physical Oceanography

210

252

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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.

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“…Le . and Richman et al (2012) recently pointed out the role of internal tides that could explain the flatter slopes.…”

Section: P Y Le Traon: From Satellite Altimetry To Argo and Operatimentioning

confidence: 99%

From satellite altimetry to Argo and operational oceanography: three revolutions in oceanography

Traon

2013

Ocean Sci.

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Abstract. The launch of the French/US mission Topex/Poseidon (T/P) (CNES/NASA) in August 1992 was the start of a revolution in oceanography. For the first time, a very precise altimeter system optimized for largescale sea level and ocean circulation observations was flying. T/P alone could not observe the mesoscale circulation. In the 1990s, the ESA satellites ERS-1/2 were flying simultaneously with T/P. Together with my CLS colleagues, we demonstrated that we could use T/P as a reference mission for ERS-1/2 and bring the ERS-1/2 data to an accuracy level comparable to T/P. Near-real-time high-resolution global sea level anomaly maps were then derived. These maps have been operationally produced as part of the SSALTO/DUACS system for the last 15 yr. They are now widely used by the oceanographic community and have contributed to a much better understanding and recognition of the role and importance of mesoscale dynamics. Altimetry needs to be complemented with global in situ observations. At the end of the 90s, a major international initiative was launched to develop Argo, the global array of profiling floats. This has been an outstanding success. Argo floats now provide the most important in situ observations to monitor and understand the role of the ocean on the earth climate and for operational oceanography. This is a second revolution in oceanography. The unique capability of satellite altimetry to observe the global ocean in near-real-time at high resolution and the development of Argo were essential for the development of global operational oceanography, the third revolution in oceanography. The Global Ocean Data Assimilation Experiment (GODAE) was instrumental in the development of the required capabilities. This paper provides an historical perspective on the development of these three revolutions in oceanography which are very much interlinked. This is not an exhaustive review and I will mainly focus on the contributions we made together with many colleagues and friends.

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Inferring dynamics from the wavenumber spectra of an eddying global ocean model with embedded tides

Cited by 97 publications

References 38 publications

Submesoscale turbulence in the upper ocean

Submesoscale turbulence in the upper ocean

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

From satellite altimetry to Argo and operational oceanography: three revolutions in oceanography

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