CoAuthors

Edward Zaron (Portland State University, U.S.)

Using multi-mission satellite altimeter data, we have developed an empirical model of the surface elevations associated with the stationary M2 internal tide. Predominantly north-south satellite track orientations and contamination from non-tidal oceanographic variability can lead to some deficiencies in the mapped tides. However, independent data from Cryosat-2 and other altimeters are used to test the solutions and show positive reduction in variance except in regions of large mesoscale variability. Thus, our new model can be used as a first-cut "correction" to altimetry to remove internal-tide signals from the data.

The tidal fields are subjected to two-dimensional wavenumber spectral analysis, which allows construction of an empirical map of modal wavelengths. Mode-1 wavelengths show good agreement with theoretical wavelengths calculated from the ocean's mean stratification, with a few localized exceptions (e.g., Tasman Sea). Mode-2 waves are detectable in much of the ocean, with wavelengths in reasonable agreement with theoretical expectations, but their spectral signatures grow too weak to map in some regions.

In the construction of the tidal solution we employ AVISO gridded sea-surface height data as a prior correction to remove non-tidal variability from the data. We examine the pros and cons of this approach, and note especially that the DUACS-2010 data are superior to the DUAC-2014 data for this task, because the newer data, while aiming for higher spatial resolution, show slightly greater evidence of leakage from tidal signals.