Characterization of internal tide incoherence : Eulerian versus
The Lagrangian and Eulerian surface current signatures of a low-mode
internal tide propagating through a turbulent balanced flow are compared
in idealized numerical simulations. 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 and larger
incoherent amplitudes. The 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 the latter
hypothesis, a theoretical model successfully predicts Lagrangian
autocovariances by relating Lagrangian and Eulerian autocovariances and
the properties of the internal tides and jet. These results have
implications for the separation of balanced flow and internal tides
signals in the sea level data collected by the future Surface Water and
Ocean Topography (SWOT) satellite mission.