North Atlantic Spectra Viewed Through an Ensemble

William Dewar (Florida State U, Tallahassee)

May 22. 2023, 09:30 — 10:15

An ensemble of eddy-rich North Atlantic simulations is analyzed, providing estimates of kinetic energy wavenumber spectra and spectral budget.  A wavelet transform technique is used to estimate a localized `pseudo-Fourier' spectrum, permitting comparisons to be made between spectra at different locations in a highly inhomogeneous and anisotropic environment.  We find evidence of a Gulf Stream imprint on the near Gulf Stream eddy field appearing as enhanced levels of energy in the North-South direction relative to the East-West direction.  Surprisingly, this signature holds into the quiescent interior.  We detect forward cascades of energy and enstrophy but find no clear evidence of upscale energy cascades in the separated Gulf Stream region.  The spectral slopes inferred from our analysis are significantly steeper than expected from quasi-geostrophic theory, but roughly in line with a primitive equation extension of the enstrophy inertial-range theory.  Lastly, we propose that the spectral shapes are somewhat universal throughout our domain, over a broad wavenumber range.  Deviations from this structure occur at high wavenumbers in locations characterized by strong surface fronts.  A summary conclusion is that expectations built on quasi-geostrophy are at best only weakly supported in primitive equations.  

Further Information
ESI Boltzmann Lecture Hall
Associated Event:
The Dynamics of Planetary-scale Fluid Flows (Thematic Programme)
Adrian Constantin (U of Vienna)
David Dritschel (U of St Andrews)
Nathan Paldor (HU of Jerusalem)