Spatial and Temporal Variability of North Atlantic Eddy Field at Scale
less than 100km.
Abstract
Ocean circulation is dominated by turbulent geostrophic eddy fields with
typical scales ranging from 10 km to 300 km. At mesoscales
(> 50 km), the size of eddy structures varies regionally
following the Rossby radius of deformation. The variability of the scale
of smaller eddies is not well known due to the limitations in existing
numerical simulations and satellite capability. But it is well
established that oceanic flows (< 50km) generally exhibit
strong seasonality. In this study, we present a basin-scale analysis of
coherent structures down to 10\,km in the North Atlantic
Ocean using two submesoscale-permitting ocean models, a NEMO-based North
Atlantic simulation with a horizontal resolution of 1/60 (NATL60) and an
HYCOM-based Atlantic simulation with a horizontal resolution of 1/50
(HYCOM50). We investigate the spatial and temporal variability of the
scale of eddy structures with a particular focus on eddies with scales
of 10 to 100\,km, and examine the impact of the
seasonality of submesoscale energy on the seasonality and distribution
of coherent structures in the North Atlantic. Our results show an
overall good agreement between the two models in terms of surface
wavenumber spectra and seasonal variability. The key findings of the
paper are that (i) the mean size of ocean eddies show strong
seasonality; (ii) this seasonality is associated with an increased
population of submesoscale eddies
(10\,–\,50\,km) in winter;
and (iii) the net release of available potential energy associated with
mixed layer instability is responsible for the emergence of the
increased population of submesoscale eddies in wintertime.