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14
2013: A multidimensional spectral description of ocean variability with applications
 Ph.D. thesis, MIT/WHOI Joint Program
"... Anupdated empirical, analyticalmodel for the frequency and wavenumber distribution of balancedmotion in the ocean is presented. The spectrummodel spans periods longer than the inertial but shorter than a decade and wavelengths between 100 and 10 000 km. Assuming geostrophic dynamics, a spectrum mode ..."
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Cited by 6 (0 self)
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Anupdated empirical, analyticalmodel for the frequency and wavenumber distribution of balancedmotion in the ocean is presented. The spectrummodel spans periods longer than the inertial but shorter than a decade and wavelengths between 100 and 10 000 km. Assuming geostrophic dynamics, a spectrum model for the streamfunction is constructed to be consistent with a range of observations, including sea surface height from satellite altimetry, velocity frommoored and shipboard instruments, and temperature frommoorings. Firstorder characteristics of the observed spectra, including amplitude and spectral moments, vary slowly geographically. The spectrum model is horizontally anisotropic, accommodating observations that zonal wavenumber–frequency spectra are dominated by a ‘‘nondispersive line.’ ’ Qualitative and quantitative agreement is found with onedimensional frequency and wavenumber spectra and observed vertical profiles of variance. Illustrative application is made of the model spectrum to observingsystem design, data mapping, and uncertainty estimation for trends. 1.
2011b Baroclinic turbulence in the ocean: analysis with primitive equation and quasigeostrophic simulations
 Journal of Physical Oceanography
"... This paper examines the factors determining the distribution, length scale, magnitude, and structure of mesoscale oceanic eddies in an eddyresolving primitive equation simulation of the Southern Ocean [Modeling Eddies in the Southern Ocean (MESO)]. In particular, the authors investigate the hypoth ..."
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This paper examines the factors determining the distribution, length scale, magnitude, and structure of mesoscale oceanic eddies in an eddyresolving primitive equation simulation of the Southern Ocean [Modeling Eddies in the Southern Ocean (MESO)]. In particular, the authors investigate the hypothesis that the primary source of mesoscale eddies is baroclinic instability acting locally on the mean state. Using local mean vertical profiles of shear and stratification from an eddying primitive equation simulation, the forced–dissipated quasigeostrophic equations are integrated in a doubly periodic domain at various locations. The scales, energy levels, and structure of the eddies found in the MESO simulation are compared to those predicted by linear stability analysis, as well as to the eddying structure of the quasigeostrophic simulations. This allows the authors to quantitatively estimate the role of local nonlinear effects and cascade phenomena in the generation of the eddy field. There is amodest transfer of energy (an ‘‘inverse cascade’’) to larger scales in the horizontal, with the length scale of the resulting eddies typically comparable to or somewhat larger than the wavelength of the most unstable mode. The eddies are, however, manifestly nonlinear, and in many locations the turbulence is fairly well developed. Coherent structures also ubiquitously emerge during the nonlinear evolution of the eddy
New Methods for Estimating Ocean Eddy Heat Transport Using Satellite Altimetry
, 2011
"... Attempts to monitor ocean eddy heat transport are strongly limited by the sparseness of available observations and the fact that heat transport is a quadratic, signindefinite quantity that is particularly sensitive to unresolved scales. In this article, a suite of stochastic filtering strategies f ..."
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Attempts to monitor ocean eddy heat transport are strongly limited by the sparseness of available observations and the fact that heat transport is a quadratic, signindefinite quantity that is particularly sensitive to unresolved scales. In this article, a suite of stochastic filtering strategies for estimating eddy heat transport are tested in idealized twolayer simulations of mesoscale oceanic turbulence at high and low latitudes under a range of observation scenarios. A novel feature of these filtering strategies is the use of computationally inexpensive stochastic models to forecast the underlying nonlinear dynamics. The stochastic model parameters can be estimated by regression fitting to climatological energy spectra and correlation times or by adaptively learning these parameters ‘‘onthefly’ ’ from the observations themselves. The authors show that, by extracting highwavenumber information that has been aliased into the low wavenumber band, ‘‘stochastically superresolved’ ’ velocity fields with a nominal resolution increase of a factor of 2 or more can be derived. Observations of the upperlayer streamfunction are projected onto an empirical orthogonal function basis for the vertical structure to produce filtered estimates for both upper and lowerlayer streamfunctions and hence net heat transport. The resulting timemean poleward eddy heat transport is significantly closer to the true value when compared with standard estimates based upon optimal interpolation. By contrast, the temporal variability of the heat transport is underestimated because of poor temporal resolution. Implications for estimating poleward eddy heat transport using current and nextgeneration altimeters are discussed. 1.
2012: Nonlinear cascade of surface oceanic geostrophic kinetic energy in the frequency domain
 J. Phys. Oceanogr
"... Motivated by the ubiquity of time series in oceanic data, the relative lack of studies of geostrophic turbulence in the frequency domain, and the interest in quantifying the contributions of intrinsic nonlinearities to oceanic frequency spectra, this paper examines the spectra and spectral fluxes of ..."
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Motivated by the ubiquity of time series in oceanic data, the relative lack of studies of geostrophic turbulence in the frequency domain, and the interest in quantifying the contributions of intrinsic nonlinearities to oceanic frequency spectra, this paper examines the spectra and spectral fluxes of surface oceanic geostrophic flows in the frequency domain. Spectra and spectral fluxes are computed from idealized twolayer quasigeostrophic (QG) turbulence models and realistic ocean general circulation models, as well as from gridded satellite altimeter data. The frequency spectra of the variance of streamfunction (akin to sea surface height) and of geostrophic velocity are qualitatively similar in all of these, with substantial variance extending out to low frequencies. The spectral flux P(v) of kinetic energy in the frequency v domain for the QG model documents a tendency for nonlinearity to drive energy toward longer periods, in likemanner to the inverse cascade toward larger length scales documented in calculations of the spectral fluxP(k) in thewavenumber k domain. Computations ofP(v) in the realistic model also display an ‘‘inverse temporal cascade.’ ’ In satellite altimeter data, some regions are dominated by an inverse temporal cascade, whereas others exhibit a forward temporal cascade. However, calculations performed with temporally and/or spatially filtered output from themodels demonstrate thatP(v) values are highly susceptible to the smoothing inherent in the construction of gridded altimeter products. Therefore, at present it is difficult to say
Frequency Domain
, 2013
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The public reporting burden tor this collection of information it estimated to average 1 hour per response, including,h # ttm *,or raviewmg instructions, searching existing data sources gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to the Department of Defense, Executive Services and Communications Directorate (07040188). Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number,
Direct Estimate of Lateral Eddy Diffusivity Upstream of Drake Passage
, 2013
"... The first direct estimate of the rate at which geostrophic turbulence mixes tracers across the Antarctic Circumpolar Current is presented. The estimate is computed from the spreading of a tracer released upstream of Drake Passage as part of the Diapycnal and Isopycnal Mixing Experiment in the Southe ..."
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The first direct estimate of the rate at which geostrophic turbulence mixes tracers across the Antarctic Circumpolar Current is presented. The estimate is computed from the spreading of a tracer released upstream of Drake Passage as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). Themeridional eddy diffusivity, a measure of the rate at which the area of the tracer spreads along an isopycnal across the Antarctic Circumpolar Current, is 7106 260m2 s21 at 1500m depth. The estimate is based on an extrapolation of the tracerbased diffusivity using output from numerical tracers released in a onetwentieth of a degree model simulation of the circulation and turbulence in the Drake Passage region. The model is shown to reproduce the observed spreading rate of the DIMES tracer and suggests that the meridional eddy diffusivity is weak in the upper kilometer of the water column with values below 500m2 s21 and peaks at the steering level, near 2 km, where the eddy phase speed is equal to the mean flow speed. These vertical variations are not captured by ocean models presently used for climate studies, but they significantly affect the ventilation of different water masses. 1.
unknown title
, 2012
"... Under consideration for publication in J. Fluid Mech. 1 Bottomtrapped currents as statistical equilibrium states above topographic anomalies ..."
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Under consideration for publication in J. Fluid Mech. 1 Bottomtrapped currents as statistical equilibrium states above topographic anomalies
ARTICLE
"... Impact of oceanicscale interactions on the seasonal modulation of ocean dynamics by the atmosphere ..."
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Impact of oceanicscale interactions on the seasonal modulation of ocean dynamics by the atmosphere