Spatial and Temporal Variability of the North Atlantic

14 Ocean circulation is dominated by turbulent geostrophic eddy fields with typical eddy scales 15 ranging from 10 km to 300 km. At mesoscales (> 50 km), the size of eddy structures varies 16 regionally following the Rossby radius of deformation. The variability of the scale of smaller 17 eddies is still not well known as a consequence of the limitations of existing numerical sim18 ulations and satellite capability. But it is well establish that submesoscale flows (< 50km) 19 generally exhibit strong seasonality. In this study, we present a basin-scale analysis of coher20 ent structures down to 10 km in the North Atlantic Ocean using two submesoscale-permitting 21 ocean models, a NEMO-based North Atlantic simulation with horizontal resolution of 1/60◦ 22 (NATL60) and a HYCOM-based Atlantic simulation with horizontal resolution of 1/50◦ 23 (HYCOM50). We investigate the spatial and temporal variability of the scale of eddy struc24 tures with a particular focus on eddies with scales of 10 to 100 km, and examine the impact 25 of the seasonality of submesoscale energy on the seasonality and distribution of coherent 26 structures in the North Atlantic. Our results show an overall good agreement between the 27 two models in terms of surface wavenumber spectra and seasonal variability. The key find28 ings of the paper are that (i) the mean size of ocean eddies show strong seasonality; (ii) 29 seasonality is associated with an increased population of submesoscale eddies (10 – 50 km) in 30 winter; and (iii) the net release of available potential energy associated with mixed layer in31 stability is responsible for the emergence of the increased population of submesoscale eddies 32 in winter time. 33 Plain Language Summary 34 The ocean is dominated by circular currents of water in swirling motion called oceanic 35 eddies. This class of motion is by far the largest reservoir of oceanic kinetic energy. Much 36 is know about this oceanic eddies at scale > 50km while we are yet to fully comprehend 37 their distribution in terms of size and dynamics at scales < 50km. This is due to the 38 lack of sufficient observational datasets at these scales in the ocean. In this study, we 39 use two kilometric resolving models of the North Atlantic ocean to investigate the spatial 40 and temporal variability of oceanic eddies down to 10km scale. Our results show that 41 the distribution of oceanic eddies at spatial scale < 100km undergo strong seasonality and 42 that this seasonality is as a result of an increased population of smaller eddies (10 50km) 43 often called submesoscales eddies in wintertime. We found that submesoscale turbulence (a 44 class of oceanic turbulence at fine-scale) is responsible for the increase in smaller scale eddy 45 distribution in winter. 46