Ocean general circulation models simulate total ocean transport averaged
over surface waves
Abstract
We argue that ocean general circulation models and observations based on
Ekman or geostrophic balance provide estimates of the Lagrangian-mean
ocean velocity field averaged over surface waves — the total
time-averaged velocity that advects oceanic tracers, particles, and
water parcels. This interpretation contradicts an assumption often made
in ocean transport studies that numerical models and observations based
on dynamical balances estimate the Eulerian-mean velocity — the
velocity time-averaged at a fixed position and only _part_ of the
total ocean velocity. Our argument uses the similarity between the
wave-averaged Lagrangian-mean momentum equations appropriate at large
oceanic scales, and the momentum equations solved by “wave-agnostic”
general circulation models that neglect surface wave effects. We further
our case by comparing a realistic, global, “wave-agnostic” general
circulation ocean model to a wave-averaged Lagrangian-mean general
circulation ocean model at eddy-permitting 1/4-degree resolution, and
find that the wave-agnostic velocity field is almost identical to the
wave-averaged Lagrangian-mean velocity.