scholarly journals Nonlinear Cascades of Surface Oceanic Geostrophic Kinetic Energy in the Frequency Domain*

2012 ◽  
Vol 42 (9) ◽  
pp. 1577-1600 ◽  
Author(s):  
Brian K. Arbic ◽  
Robert B. Scott ◽  
Glenn R. Flierl ◽  
Andrew J. Morten ◽  
James G. Richman ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Frequency Domain ◽  
General Circulation ◽  
General Circulation Models ◽  
Altimeter Data ◽  
Satellite Altimeter ◽  
Frequency Spectra ◽  
Low Frequencies ◽  
Spectral Flux ◽  
Satellite Altimeter Data

Abstract 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 two-layer 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 Π(ω) of kinetic energy in the frequency ω domain for the QG model documents a tendency for nonlinearity to drive energy toward longer periods, in like manner to the inverse cascade toward larger length scales documented in calculations of the spectral flux Π(k) in the wavenumber k domain. Computations of Π(ω) 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 the models demonstrate that Π(ω) values are highly susceptible to the smoothing inherent in the construction of gridded altimeter products. Therefore, at present it is difficult to say whether the forward temporal cascades seen in some regions in altimeter data represent physics that is missing in the models studied here or merely sampling artifacts.

Barotropic and baroclinic inverse kinetic energy cascade in the Antarctic Circumpolar Current

2021 ◽  
Author(s):  
Hongjie Li ◽  
Yongsheng Xu
Keyword(s):  
Kinetic Energy ◽  
General Circulation ◽  
Antarctic Circumpolar Current ◽  
General Circulation Models ◽  
Energy Cascade ◽  
Turbulence Theory ◽  
Inverse Cascade ◽  
Spectral Flux ◽  
Circumpolar Current ◽  
The Antarctic

AbstractStratified geostrophic turbulence theory predicts an inverse energy cascade for the barotropic (BT) mode. Satellite altimetry has revealed a net inverse cascade in the baroclinic (BC) mode. Here the spatial variabilities of BT and BC kinetic energy fluxes in the Antarctic Circumpolar Current (ACC) were investigated using ECCO2 data, which synthesizes satellite data and in situ measurements with an eddy-permitting general circulation models containing realistic bathymetry and wind forcing. The BT and BC inverse kinetic energy cascades both reveal complex spatial variations that could not be explained fully by classical arguments. For example, the BC injection scales match better with most unstable scales than with the first-mode deformation scales, but the opposite is true for the BT mode. In addition, the BT and BC arrest scales do not follow the Rhines scale well in term of spatial variation, but show better consistency with their own energy-containing scales. The reverse cascade of the BT and BC modes was found related to their EKE, and better correlation was found between the BT inverse cascade and barotropization. Speculations of the findings were proposed. however, further observations and modeling experiments are needed to test these interpretations. Spectral flux anisotropy exhibits a feature associated with oceanic jets that is consistent with classical expectations. Specifically, the spectral flux along the along-stream direction remains negative at scales up to that of the studied domain (~2000km), while that in the perpendicular direction becomes positive close to the scale of the width of a typical jet.

scholarly journals Geostrophic Turbulence in the Frequency–Wavenumber Domain: Eddy-Driven Low-Frequency Variability*

2014 ◽  
Vol 44 (8) ◽  
pp. 2050-2069 ◽  
Author(s):  
Brian K. Arbic ◽  
Malte Müller ◽  
James G. Richman ◽  
Jay F. Shriver ◽  
Andrew J. Morten ◽  
...  
Keyword(s):  
High Resolution ◽  
Kinetic Energy ◽  
General Circulation Model ◽  
General Circulation ◽  
Low Frequency ◽  
Circulation Model ◽  
Satellite Altimeter ◽  
Low Frequencies ◽  
Low Frequency Variability ◽  
Geostrophic Turbulence

Abstract Motivated by the potential of oceanic mesoscale eddies to drive intrinsic low-frequency variability, this paper examines geostrophic turbulence in the frequency–wavenumber domain. Frequency–wavenumber spectra, spectral fluxes, and spectral transfers are computed from an idealized two-layer quasigeostrophic (QG) turbulence model, a realistic high-resolution global ocean general circulation model, and gridded satellite altimeter products. In the idealized QG model, energy in low wavenumbers, arising from nonlinear interactions via the well-known inverse cascade, is associated with energy in low frequencies and vice versa, although not in a simple way. The range of frequencies that are highly energized and engaged in nonlinear transfer is much greater than the range of highly energized and engaged wavenumbers. Low-frequency, low-wavenumber energy is maintained primarily by nonlinearities in the QG model, with forcing and friction playing important but secondary roles. In the high-resolution ocean model, nonlinearities also generally drive kinetic energy to low frequencies as well as to low wavenumbers. Implications for the maintenance of low-frequency oceanic variability are discussed. The cascade of surface kinetic energy to low frequencies that predominates in idealized and realistic models is seen in some regions of the gridded altimeter product, but not in others. Exercises conducted with the general circulation model suggest that the spatial and temporal filtering inherent in the construction of gridded satellite altimeter maps may contribute to the discrepancies between the direction of the frequency cascade in models versus gridded altimeter maps seen in some regions. Of course, another potential reason for the discrepancy is missing physics in the models utilized here.

scholarly journals On Eddy Viscosity, Energy Cascades, and the Horizontal Resolution of Gridded Satellite Altimeter Products*

2013 ◽  
Vol 43 (2) ◽  
pp. 283-300 ◽  
Author(s):  
Brian K. Arbic ◽  
Kurt L. Polzin ◽  
Robert B. Scott ◽  
James G. Richman ◽  
Jay F. Shriver
Keyword(s):  
General Circulation ◽  
Eddy Viscosity ◽  
Accurate Determination ◽  
General Circulation Models ◽  
Horizontal Resolution ◽  
Altimeter Data ◽  
Satellite Altimeter ◽  
Inverse Cascade ◽  
Present Generation ◽  
Wide Swath

Abstract Motivated by the recent interest in ocean energetics, the widespread use of horizontal eddy viscosity in models, and the promise of high horizontal resolution data from the planned wide-swath satellite altimeter, this paper explores the impacts of horizontal eddy viscosity and horizontal grid resolution on geostrophic turbulence, with a particular focus on spectral kinetic energy fluxes Π(K) computed in the isotropic wavenumber (K) domain. The paper utilizes idealized two-layer quasigeostrophic (QG) models, realistic high-resolution ocean general circulation models, and present-generation gridded satellite altimeter data. Adding horizontal eddy viscosity to the QG model results in a forward cascade at smaller scales, in apparent agreement with results from present-generation altimetry. Eddy viscosity is taken to roughly represent coupling of mesoscale eddies to internal waves or to submesoscale eddies. Filtering the output of either the QG or realistic models before computing Π(K) also greatly increases the forward cascade. Such filtering mimics the smoothing inherent in the construction of present-generation gridded altimeter data. It is therefore difficult to say whether the forward cascades seen in present-generation altimeter data are due to real physics (represented here by eddy viscosity) or to insufficient horizontal resolution. The inverse cascade at larger scales remains in the models even after filtering, suggesting that its existence in the models and in altimeter data is robust. However, the magnitude of the inverse cascade is affected by filtering, suggesting that the wide-swath altimeter will allow a more accurate determination of the inverse cascade at larger scales as well as providing important constraints on smaller-scale dynamics.

scholarly journals Surface Geostrophic Circulation of the Mediterranean Sea Derived from Drifter and Satellite Altimeter Data

2012 ◽  
Vol 42 (6) ◽  
pp. 973-990 ◽  
Author(s):  
Pierre-Marie Poulain ◽  
Milena Menna ◽  
Elena Mauri
Keyword(s):  
Kinetic Energy ◽  
Mediterranean Sea ◽  
Surface Waters ◽  
Energy Levels ◽  
Altimeter Data ◽  
Mean Flow ◽  
Satellite Altimeter ◽  
The Mean ◽  
Surface Geostrophic Circulation ◽  
Satellite Altimeter Data

Abstract Drifter observations and satellite-derived sea surface height data are used to quantitatively study the surface geostrophic circulation of the entire Mediterranean Sea for the period spanning 1992–2010. After removal of the wind-driven components from the drifter velocities and low-pass filtering in bins of 1° × 1° × 1 week, maps of surface geostrophic circulation (mean flow and kinetic energy levels) are produced using the drifter and/or satellite data. The mean currents and kinetic energy levels derived from the drifter data appear stronger/higher with respect to those obtained from satellite altimeter data. The maps of mean circulation estimated from the drifter data and from a combination of drifter and altimeter data are, however, qualitatively similar. In the western basin they show the main pathways of the surface waters flowing eastward from the Strait of Gibraltar to the Sicily Channel and the current transporting waters back westward along the Italian, French, and Spanish coasts. Intermittent and long-lived subbasin-scale eddies and gyres abound in the Tyrrhenian and Algerian Seas. In the eastern basin, the surface waters are transported eastward by several currents but recirculate in numerous eddies and gyres before reaching the northward coastal current off Israel, Lebanon, and Syria and veering westward off Turkey. In the Ionian Sea, the mean geostrophic velocity maps were also produced separately for the two extended seasons and for multiyear periods. Significant variations are confirmed, with seasonal reversals of the currents in the south and changes of the circulation from anticyclonic (prior to 1 July 2007) to cyclonic and back to anticyclonic after 31 December 2005.

A Feasibility Demonstration of Ocean Model Eddy-resolving Nowcast/Forecast Skill Using Satellite Altimeter Data

2000 ◽  
Author(s):  
Harley E. Hurlburt ◽  
Robert C. Rhodes ◽  
Charlie N. Barron ◽  
E. J. Metzger ◽  
Ole M. Smedstad
Keyword(s):  
Ocean Model ◽  
Forecast Skill ◽  
Altimeter Data ◽  
Satellite Altimeter ◽  
Satellite Altimeter Data

Estimating discharge of the Ganga River from satellite altimeter data

2021 ◽  
pp. 126860
Author(s):  
Atul Kumar Rai ◽  
Zafar Beg ◽  
Abhilash Singh ◽  
Kumar Gaurav
Keyword(s):  
Ganga River ◽  
Altimeter Data ◽  
Satellite Altimeter ◽  
Satellite Altimeter Data
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