An Approach to Empirical Mapping of Incoherent Internal Tides With Altimetry Data

Much of the internal tide (IT) is coherent with tidal forcing, but interactions with time-varying ocean flows result in an incoherent component of IT (IIT), which will complicate interpretation of data from the upcoming Surface Water Ocean Topography (SWOT) mission. Here, we demonstrate a simple scheme for estimation of these IIT. We use a short-time harmonic analysis of outputs of a wind- and tidally forced ocean model to generate an ensemble of IT variations in an ocean patch. Principal Components Analysis is used to define the dominant spatial patterns, and combined with sinusoidal time variations at tidal frequencies to define spatio-temporal basis functions that are used to fit sparse altimetry data available in short time windows. The scheme is illustrated using a 1-yr Hybrid Coordinate Ocean Model (HYCOM) run off the Amazon Shelf. Tests with synthetic (SWOT) and real (nadir altimetry) data demonstrate that a significant fraction of IIT can be recovered with this procedure.