A high-resolution simulation of the ocean during the POMME experiment:: Mesoscale variability and near surface processes

[ 1] This article is the second part of a modeling study of upper ocean mesoscale physical processes in an area of the northeast Atlantic that was extensively sampled during the Programme Ocean Multidisciplinaire Meso-Echelle (POMME experiment, October 2000 - September 2001). The model is a high-resolution regional version of the ocean general circulation model OPA integrated from February to May 2001. The mesoscale upper ocean dynamics has been carefully validated in a first paper (Paci et al., 2005). In the present article, the simulation is used to analyze the contribution of mesoscale eddies to the mixed layer processes during the period that controls the annual subduction rate and the characteristics of the subducted water. Mesoscale eddies account for a significant part of the mixed layer heat, salt, and water budgets through mesoscale and submesoscale structures acting on the horizontal advective terms. They represent respectively 52% and 66% of the horizontal advection of temperature and salinity and 70% of the lateral induction. They also induce an earlier and more intense restratification. The domain-averaged detrainment appears to be reduced by more than 15% by mesoscale eddies and reaches about 0.8 Sv. However, these eddies increase the density of the detrained water. Some dense water, likely to be involved in the formation of subpolar mode water, is detrained by them in a way that maximizes its chance to be effectively subducted in the area.