Oceanography

Optics

Wavenumber

Physics

Geology

Astronomy

Sea surface temperature

Sea-surface height

Meteorology

Composite material

Eddy

Ocean current

Ecology

Materials science

Turbulence

Range (aeronautics)

Spectral slope

Temporal scales

Circumpolar star

Environmental science

Mesoscale meteorology

Spectral line

Climatology

Biology

Atmospheric sciences

Nature Communications

Advent of satellite altimetry brought into focus the pervasiveness of mesoscale eddies                                                                   $${{{{{{{\bf{{{{{{{{\mathcal{O}}}}}}}}}}}}}}}}({100})$$                               km in size, which are the ocean’s analogue of weather systems and are often regarded as the spectral peak of kinetic energy (KE). Yet, understanding of the ocean’s spatial scales has been derived mostly from Fourier analysis in small "representative” regions that cannot capture the vast dynamic range at planetary scales. Here, we use a coarse-graining method to analyze scales much larger than what had been possible before. Spectra spanning over three decades of length-scales reveal the Antarctic Circumpolar Current as the spectral peak of the global extra-tropical circulation, at ≈ 104 km, and a previously unobserved power-law scaling over scales larger than 103 km. A smaller spectral peak exists at ≈ 300 km associated with mesoscales, which, due to their wider spread in wavenumber space, account for more than 50% of resolved surface KE globally. Seasonal cycles of length-scales exhibit a characteristic lag-time of ≈ 40 days per octave of length-scales such that in both hemispheres, KE at 102 km peaks in spring while KE at 103 km peaks in late summer. These results provide a new window for understanding the multiscale oceanic circulation within Earth’s climate system, including the largest planetary scales. Ocean spatial scale analysis has struggled to capture the vast dynamic range at planetary scales. Here the authors employ a method to probe circulation patterns in the World Ocean, thus opening a promising new window for measuring and understanding the ocean’s role in Earth’s climate system.

Global energy spectrum of the general oceanic circulation