Joint estimation of balanced motions and internal tides from future wide‐swath altimetry

Type Article
Date 2021-12
Language English
Author(s) Le Guillou FlorianORCID1, Lahaye NoeORCID2, Ubelmann Clément3, Metref Sammy1, Cosme Emmanuel1, Ponte AurelienORCID4, Le Sommer Julien1, Blayo Eric5, Vidard ArthurORCID5
Affiliation(s) 1 : Univ. Grenoble Alpes ,CNRS IRD Grenoble INP IGE Grenoble, France
2 : Inria & IRMAR campus universitaire de Beaulieu Rennes, France
3 : Ocean Next ,Grenoble ,France
4 : Univ. Brest CNRS IRD Ifremer Laboratoire d’Oceanographie Physique et Spatiale (LOPS) IUEM Brest , France
5 : Univ. Grenoble Alpes CNRS INRIA Grenoble INP LJK Grenoble ,France
Source Journal Of Advances In Modeling Earth Systems (1942-2466) (American Geophysical Union (AGU)), 2021-12 , Vol. 13 , N. 12 , P. e2021MS002613 (17p.)
DOI 10.1029/2021MS002613
Keyword(s) sea, ocean surface, altimetry, data assimilation
Abstract

Wide-swath altimetry, e.g. the Surface Water and Ocean Topography (SWOT) mission is expected to 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 (BMs) and another component due to internal tides (ITs). 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 BMs, and a linear shallow-water model with 4-Dimensional Variational (4DVar) assimilation for ITs. 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 mode-one ITs. The algorithm reconstructs almost 80% of the variance of BMs and ITs, 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 ITs, the amplitude and phase of nonstationary ITs are reconstructed. Sensitivity experiments show that the quality of reconstruction significantly depends upon the timing of observations. Although idealized, this study represents a step forward towards the disentanglement of BMs and ITs signals from real wide-swath altimetry data.

Plain Language Summary

Wide-swath altimetry, e.g. the Surface Water and Ocean Topography (SWOT) mission is expected to provide Sea Surface Height (SSH) images with pixels of 2 km, revealing motions at scales of a few tens of kilometers. At these scales, SSH variations are essentially due to the superposition of slow, balanced motions primarily constrain by Earth’s rotation, and fast, propagating motions due to internal waves mainly generated by interactions between bathymetry and tidal water displacements. Several oceanographic applications require the separation of these two SSH components and their mapping on regular grids. This paper presents an original method to achieve this separation, based on data assimilation approaches and simple dynamical models. Experiments with synthetic SSH images, simulated from an ocean circulation model with detailed physics, show the efficiency of the method.

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Le Guillou Florian, Lahaye Noe, Ubelmann Clément, Metref Sammy, Cosme Emmanuel, Ponte Aurelien, Le Sommer Julien, Blayo Eric, Vidard Arthur (2021). Joint estimation of balanced motions and internal tides from future wide‐swath altimetry. Journal Of Advances In Modeling Earth Systems, 13(12), e2021MS002613 (17p.). Publisher's official version : https://doi.org/10.1029/2021MS002613 , Open Access version : https://archimer.ifremer.fr/doc/00735/84741/