Presenter: Zoé Caspar-Cohen (LOPS, Ifremer)

Description:
The separation of balanced flow and internal tides signals is expected to be a challenge in the sea level data collected by the future Surface Water and Ocean Topography (SWOT) satellite mission. We advocate that drifters data can provide useful information about internal tide properties in order to mitigate if not overcome this challenge. In order to investigate this idea, we extract and compare internal tide signatures (e.g. level of incoherence, amplitudes) in Eulerian and Lagrangian frames of reference, in an idealized simulation. Lagrangian and Eulerian total (i.e. coherent plus incoherent) tidal amplitudes are found to be similar. Compared to Eulerian diagnostics, the Lagrangian tidal signal is more incoherent with comparable or smaller incoherence timescales. This larger level of incoherence in Lagrangian data is proposed to result from the deformation of Eulerian internal tide signal induced by drifter displacements. Based on this hypothesis, a theoretical model successfully predicts Lagrangian autocovariances from Eulerian autocovariances and properties of the internal tides and jet. These encouraging results are then extended to a more realistic configuration using MITgcm LLC4320 simulation.