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Spatio-temporal coarse-graining decomposition of the global ocean geostrophic kinetic energy
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  • Michele Buzzicotti,
  • Benjamin A Storer,
  • Hemant Khatri,
  • Stephen M Griffies,
  • Hussein Aluie
Michele Buzzicotti
University of Rome Tor Vergata
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Benjamin A Storer
University of Rochester
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Hemant Khatri
University of Liverpool
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Stephen M Griffies
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Hussein Aluie
University of Rochester

Corresponding Author:hussein@rochester.edu

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We expand on a recent determination of the first global energy spectrum of the ocean’s surface geostrophic circulation \cite{Storer2022} using a coarse-graining (CG) method. We compare spectra from CG to those from spherical harmonics by treating land in a manner consistent with the boundary conditions. While the two methods yield qualitatively consistent domain-averaged results, spherical harmonics spectra are too noisy at gyre-scales ($>1000 $km). More importantly, spherical harmonics are inherently global and cannot provide local information connecting scales with currents geographically. CG shows that the extra-tropics mesoscales (100–500 km) have a root-mean-square (rms) velocity of $\sim15 $cm/s, which increases to $\sim30$–40 cm/s locally in the Gulf Stream and Kuroshio and to $\sim16$–28 cm/s in the ACC. There is notable hemispheric asymmetry in mesoscale energy-per-area, which is higher in the north due to continental boundaries. We estimate that $\approx25$–50\% of total geostrophic energy is at scales smaller than 100 km, and is un(der)-resolved by pre-SWOT satellite products. Spectra of the time-mean component show that most of its energy (up to $70\%$) resides in stationary mesoscales ($<500 $km), highlighting the preponderance of ‘standing’ small-scale structures in the global ocean. By coarse-graining in space and time, we compute the first spatio-temporal global spectrum of geostrophic circulation from AVISO and NEMO. These spectra show that every length-scale evolves over a wide range of time-scales with a consistent peak at $\approx200$ km and $\approx2$–3 weeks.
15 May 2023Submitted to ESS Open Archive
25 May 2023Published in ESS Open Archive