Wind-Forced Submesoscale Symmetric Instability around Deep Convection in the Northwestern Mediterranean Sea
Résumé
During the winter from 2009 to 2013, the mixed layer reached the seafloor at about 2500min
the northwestern Mediterranean Sea. Intense fronts around the deep convection area were repeatedly
sampled by autonomous gliders. Subduction down to 200–300 m, sometimes deeper, below the
mixed layer was regularly observed testifying of important frontal vertical movements. Potential
Vorticity dynamics was diagnosed using glider observations and a high resolution realistic model
at 1-km resolution. During down-front wind events in winter, remarkable layers of negative PV
were observed in the upper 100m on the dense side of fronts surrounding the deep convection area
and successfully reproduced by the numerical model. Under such conditions, symmetric instability
can grow and overturn water along isopycnals within typically 1–5 km cross-frontal slanted cells.
Two important hotpspots for the destruction of PV along the topographically-steered Northern
Current undergoing frequent down-front winds have been identified in the western part of Gulf of
Lion and Ligurian Sea. Fronts were there symmetrically unstable for up to 30 days per winter in
the model, whereas localized instability events were found in the open sea, mostly influenced by
mesoscale variability. The associated vertical circulations also had an important signature on oxygen
and fluorescence, highlighting their under important role for the ventilation of intermediate layers,
phytoplankton growth and carbon export.
Domaines
Océan, Atmosphère| Origine | Fichiers éditeurs autorisés sur une archive ouverte |
|---|
