Accuracy assessment of global internal-Tide models using satellite altimetry

Abstract

Altimeter measurements are corrected for several geophysical parameters in order to access ocean signals of interest, like mesoscale or sub-mesoscale variability. The ocean tide is one of the most critical corrections due to the amplitude of the tidal elevations and to the aliasing phenomena of high-frequency signals into the lower-frequency band, but the internal-Tide signatures at the ocean surface are not yet corrected globally. Internal tides can have a signature of several centimeters at the surface with wavelengths of about 50-250 km for the first mode and even smaller scales for higher-order modes. The goals of the upcoming Surface Water Ocean Topography (SWOT) mission and other high-resolution ocean measurements make the correction of these small-scale signals a challenge, as the correction of all tidal variability becomes mandatory to access accurate measurements of other oceanic signals. In this context, several scientific teams are working on the development of new internal-Tide models, taking advantage of the very long altimeter time series now available, which represent an unprecedented and valuable global ocean database. The internal-Tide models presented here focus on the coherent internal-Tide signal and they are of three types: empirical models based upon analysis of existing altimeter missions, an assimilative model and a three-dimensional hydrodynamic model. span idCombining double low line"page148"/>A detailed comparison and validation of these internal-Tide models is proposed using existing satellite altimeter databases. The analysis focuses on the four main tidal constituents: Mspan classCombining double low line"inline-formula">2/span>, Kspan classCombining double low line"inline-formula">1/span>, Ospan classCombining double low line"inline-formula">1/span> and Sspan classCombining double low line"inline-formula">2/span>. The validation process is based on a statistical analysis of multi-mission altimetry including Jason-2 and Cryosphere Satellite-2 data. The results show a significant altimeter variance reduction when using internal-Tide corrections in all ocean regions where internal tides are generating or propagating. A complementary spectral analysis also gives some estimation of the performance of each model as a function of wavelength and some insight into the residual non-stationary part of internal tides in the different regions of interest. This work led to the implementation of a new internal-Tide correction (ZARON'one) in the next geophysical data records version-F (GDR-F) standards.