Joint estimation of balanced motions and internal tides from future
wide-swath altimetry
Abstract
The future Surface Water and Ocean Topography (SWOT) mission will soon
provide Sea Surface Height (SSH) measurements resolving scales of a few
tens of kilometers. Over a large fraction of the globe, the SSH signal
at these scales is essentially a superposition of a component due to
balanced motions (BM) and another component due to internal tides (IT).
Several oceanographic applications require the separation of these
components and their mapping on regular grids. For that purpose, the
paper introduces an alternating minimization algorithm that iteratively
implements two data assimilation techniques, each specific to the
mapping of one component: a quasi-geostrophic model with Back-and-Forth
Nudging for BM, and a linear shallow-water model with 4-Dimensional
Variational (4DVar) assimilation for IT. The algorithm is tested with
Observation System Simulation Experiments (OSSE) where the truth is
provided by a primitive-equation ocean model in an idealized
configuration simulating a turbulent jet and a mode-one IT. The
algorithm reconstructs almost 80\% of the variance of BM
and IT, the remaining 20\% being mostly due to dynamics
that cannot be described by the simple models used. Importantly, in
addition to the reconstruction of stationary IT, the amplitude and phase
of nonstationary IT are reconstructed. Although idealized, this study
represents a step forward towards the disentanglement of BM and IT
signals from real SWOT data.