Characterization of internal tide non-stationarity : Eulerian versus
Lagrangian perspectives
Abstract
The Lagrangian and Eulerian near-surface current signatures of a
low-mode internal tide propagating through a turbulent jet are compared
in an idealized numerical simulation. We estimate and compare internal
tides’ stationary and nonstationary velocity amplitudes as well as
non-stationarity timescales. We find Lagrangian internal tides total
amplitude similar to Eulerian one. Lagrangian velocity are mostly
nonstationary and Lagrangian non-stationary timescales are comparable to
or smaller than Eulerian ones. This low-bias is proposed to be the
result of the deformation of internal tide surface signal along the
drift induced by lower frequency surface currents. A model based on the
latter hypothesis successfully predicts Lagrangian autocovariance and
highlights its dependence to Eulerian autocovariance and to the
properties of the internal tides and jet. We address the implications of
these results in the context of the Surface Water and Ocean Topography
(SWOT) mission, for which the separation of mesoscale balanced flow and
internal tides with data at the ocean’s surface was raised.