Intense deformation field at oceanic front inferred from directional sea surface roughness observations

Nicolas Rascle (1) , Jeroen Molemaker (1) , Louis Marié (1) , Frédéric Nouguier , Bertrand Chapron (1) , Björn Lund , Alexis Mouche (1)

1 LOPS - Laboratoire d'Océanographie Physique et Spatiale

Fine-scale current gradients at the ocean surface can be observed by sea surface roughness. More specifically, directional surface roughness anomalies are related to the different horizontal current gradient components. This paper reports results from a dedicated experiment during the Lagrangian Submesoscale Experiment (LASER) drifter deployment. A very sharp front, 50 m wide, is detected simultaneously in drifter trajectories, sea surface temperature, and sea surface roughness. A new observational method is applied, using Sun glitter reflections during multiple airplane passes to reconstruct the multiangle roughness anomaly. This multiangle anomaly is consistent with wave-current interactions over a front, including both cross-front convergence and along-front shear with cyclonic vorticity. Qualitatively, results agree with drifters and X-band radar observations. Quantitatively, the sharpness of roughness anomaly suggests intense current gradients, 0.3 m s^-1 over the 50 m wide front. This work opens new perspectives for monitoring intense oceanic fronts using drones or satellite constellations.

Mots clés: sea surface roughness; surface current; remote sensing; Sun glitter; high resolution; oceanic fronts

Domaines: Planète et Univers [physics]

Nicolas Rascle, Jeroen Molemaker, Louis Marié, Frédéric Nouguier, Bertrand Chapron, et al.. Intense deformation field at oceanic front inferred from directional sea surface roughness observations. Geophysical Research Letters, 2017, 44, pp.5599-5608. ⟨10.1002/2017GL073473⟩. ⟨insu-03682748⟩