Diagnosing cross-scale kinetic energy exchanges from two submesoscale
permitting ocean models.
Abstract
Fine-scale motions ($<$100 km) contribute significantly to
the exchanges and dissipation of kinetic energy in the upper ocean.
However, knowledge of ocean kinetic energy at fine-scales (in terms of
density and transfers) is currently limited due to the lack of
sufficient observational datasets at these scales. The sea-surface
height measurements of the upcoming SWOT altimeter mission should
provide information on kinetic energy exchanges in the upper ocean down
to 10-15 km. Numerical ocean models, able to describe ocean dynamics
down to $\sim$10 km, have been developed in
anticipation of the SWOT mission. In this study, we use two
state-of-the-art, realistic, North Atlantic simulations, with horizontal
resolutions $ \sim $ 1.5 km, to investigate the
distribution and exchanges of kinetic energy at fine-scales in the open
ocean. Our results show that the distribution of kinetic energy at
fine-scales approximately follows the predictions of quasi-geostrophic
dynamics in summertime but is somewhat consistent with submesoscale
fronts-dominated regimes in wintertime. The kinetic energy spectral
fluxes are found to exhibit both inverse and forward cascade over the
top 1000 m, with a maximum inverse cascade close to the average
energy-containing scale. The forward cascade is confined to the ocean
surface and shows a strong seasonality, both in magnitude and range of
scales affected. Our analysis further indicates that high-frequency
motions ($<$1day) play a key role in the forward cascade and
that the estimates of the spectral fluxes based on geostrophic
velocities fail to capture some quantitative aspects of kinetic energy
exchanges across scales.