Global Wavenumber Spectrum with Corrections for Altimeter High-Frequency Noise

Zhou, Xiangxian; Wang, Dongping; Chen, Dake

doi:10.1175/jpo-d-14-0144.1

Cited by 19 publications

(47 citation statements)

References 23 publications

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“…The local maximum of

L_{i n j}

in high‐energy predominantly eastward‐flowing currents, which is much obvious in Figures b and c, may be consistent with the results of global SSH spectrum analysis [ Xu and Fu , ; Zhou et al ., ]. Xu and Fu [] diagnosed the global variability of the spectrum using the altimeter‐observed SSH and found that SSH spectral slopes are deeper in the high EKE regions, such as the ACC, the Gulf Stream, and the Kuroshio Extension.…”

Section: Resultsmentioning

confidence: 99%

Geographical distribution and anisotropy of the inverse kinetic energy cascade, and its role in the eddy equilibrium processes

Wang

Liu

Pang

2015

J. Geophys. Res. Oceans

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The geographic character of the inverse cascade is analyzed based on the spectral kinetic energy flux calculated in the global ocean, using sea surface height (SSH) data from satellites, reanalysis data, and model outputs. It is shown that the strongest inverse cascade occurs mostly in high-energy eastward-flowing currents, such as the Antarctic Circumpolar Current (ACC), the Kuroshio Extension, and the Gulf Stream, which matches the global distribution pattern of the eddy kinetic energy (EKE). Hence, the eddy scales predicted by the local linear baroclinic instability L bci and from the altimeter observation L eddy are mapped out and compared with the energy injection scale L inj and the arrest-start scale L arrest2start of the inverse cascade, respectively. Generally, L bci agrees well with L inj in the midlatitude and high-latitude oceans, especially in the Northern Hemisphere. L eddy falls within the arrest ranges of the inverse cascade and is quite close to L arrest2start . Finally, the depth dependence and the anisotropy of the inverse kinetic energy cascade are also diagnosed in the global ocean. We have found that the strength of the inverse cascades decreases with increasing depth, but the global pattern of the strength is nearly invariable. Meanwhile, the variations in depth hardly affect the L inj and L arrest2start . After considering the anisotropy in the spectral flux calculation, a possible inertial range for the zonal spectral kinetic energy flux is expected, where the cascade magnitude will keep a nearly constant negative value associated with the oceanic zonal jets.

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“…The local maximum of

L_{i n j}

Section: Resultsmentioning

confidence: 99%

Geographical distribution and anisotropy of the inverse kinetic energy cascade, and its role in the eddy equilibrium processes

Wang

Liu

Pang

2015

J. Geophys. Res. Oceans

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“…The intermediate white spectrum for scales between about 5 and 15 km is referred to as a spectral hump and is associated with blooms of normalized radar backscatter s 0 or rain contamination (Dibarboure et al 2014). While there have been suggestions for strategies to remove the spectral hump (e.g., Xu and Fu 2012;Zhou et al 2015) to obtain consistent spectral slopes, we opt not to apply these approaches here and instead truncate our spectral interpretation at about 30 km.…”

Section: Satellite Altimetry a The Saral/altika Altimetermentioning

confidence: 99%

Mesoscale to Submesoscale Wavenumber Spectra in Drake Passage

Rocha

Chereskin

Gille

et al. 2016

Journal of Physical Oceanography

243

300

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This study discusses the upper-ocean (0-200 m) horizontal wavenumber spectra in the Drake Passage from 13 yr of shipboard ADCP measurements, altimeter data, and a high-resolution numerical simulation. At scales between 10 and 200 km, the ADCP kinetic energy spectra approximately follow a k 23 power law. The observed flows are more energetic at the surface, but the shape of the kinetic energy spectra is independent of depth. These characteristics resemble predictions of isotropic interior quasigeostrophic turbulence. The ratio of across-track to along-track kinetic energy spectra, however, significantly departs from the expectation of isotropic interior quasigeostrophic turbulence. The inconsistency is dramatic at scales smaller than 40 km. A Helmholtz decomposition of the ADCP spectra and analyses of synthetic and numerical model data show that horizontally divergent, ageostrophic flows account for the discrepancy between the observed spectra and predictions of isotropic interior quasigeostrophic turbulence. In Drake Passage, ageostrophic motions appear to be dominated by inertia-gravity waves and account for about half of the near-surface kinetic energy at scales between 10 and 40 km. Model results indicate that ageostrophic flows imprint on the sea surface, accounting for about half of the sea surface height variance between 10 and 40 km.

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“…Current altimeters provide measurements of SSH along the satellite track with a sampling frequency of 20 Hz, implying a spatial resolution on the order of ∼ 300 m. The power spectral density (PSD) of these measurements shows the presence of white noise (e.g., Le Traon et al, 2008;Fu, 2011, 2012;Dibarboure et al, 2014;Zhou et al, 2015), which is a major limiting factor for the estimation of ocean currents. Since noise has a stronger effect on small-scales it is common to (low-pass) filter altimetric measurements before computing velocities.…”

Section: Currents From Sea Surface Heightmentioning

confidence: 99%

Remote sensing of ocean surface currents: a review of what is being observed and what is being assimilated

Isern‐Fontanet

Ballabrera-Poy

Turiel

et al. 2017

Nonlin. Processes Geophys.

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Abstract. Ocean currents play a key role in Earth's climate -they impact almost any process taking place in the ocean and are of major importance for navigation and human activities at sea. Nevertheless, their observation and forecasting are still difficult. First, no observing system is able to provide direct measurements of global ocean currents on synoptic scales. Consequently, it has been necessary to use sea surface height and sea surface temperature measurements and refer to dynamical frameworks to derive the velocity field. Second, the assimilation of the velocity field into numerical models of ocean circulation is difficult mainly due to lack of data. Recent experiments that assimilate coastal-based radar data have shown that ocean currents will contribute to increasing the forecast skill of surface currents, but require application in multidata assimilation approaches to better identify the thermohaline structure of the ocean. In this paper we review the current knowledge in these fields and provide a global and systematic view of the technologies to retrieve ocean velocities in the upper ocean and the available approaches to assimilate this information into ocean models.

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Global Wavenumber Spectrum with Corrections for Altimeter High-Frequency Noise

Cited by 19 publications

References 23 publications

Geographical distribution and anisotropy of the inverse kinetic energy cascade, and its role in the eddy equilibrium processes

Geographical distribution and anisotropy of the inverse kinetic energy cascade, and its role in the eddy equilibrium processes

Mesoscale to Submesoscale Wavenumber Spectra in Drake Passage

Remote sensing of ocean surface currents: a review of what is being observed and what is being assimilated

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