A synthesis of upper ocean geostrophic kinetic energy spectra from a
global submesoscale permitting simulation
Abstract
A submesoscale-permitting global ocean model is used to study the upper
ocean turbulence. Submesoscale processes peak in winter and,
consequently, geostrophic kinetic energy (KE) spectra tend to be
relatively shallow in winter (∼k-2) with steeper
spectra in summer (∼k-3). This seasonal transition
from steep to shallow power-law in the KE spectra indicates a transition
from quasi-geostrophic (QG) turbulence in summer to pronounced
surface-QG-like turbulence in winter. It is shown that this transition
in KE spectral scaling has two phases. In the first phase (late autumn),
KE spectra show a presence of two spectral regimes:
∼k-3 scaling in mesoscales (100-300 km) and
∼k-2 scaling in submesoscales (<50 km),
indicating the coexistence of QG, surface-QG, and frontal dynamics. In
the second phase (late winter), mixed-layer instabilities convert
available potential energy into KE, which cascades upscale leading to
flattening of the KE spectra at larger scales, and k-2
power-law develops in mesoscales too.