Loren Carrere (CLS, France); Gérald Dibarboure (CNES, France); Maxime Ballarotta (CLS, France); Clement Ubelmann (Datlas, France)

An internal tide (IT) is an internal wave that varies at the tidal frequency and can be observed by altimetry. There are two types of internal tide: a coherent or stationary internal tide, which is in phase with the barotropic tide; and an incoherent or non-stationary internal tide, which results from the interaction between the internal tide and its propagation environment. This work aims to contribute to the improvement of the knowledge and the correction of the non-stationary part of IT in the ocean and is within the scope of several projects (Tide-SALP and TOSCA-SCOEPUS).

In this study, we present a test case for correcting the coherent and incoherent internal tides in the altimetric SLA (Sea Level Anomaly) i.e. an internal tide correction in two stages. The 2023 SLA from six missions (S3a, S3b, C2, H2b and J3) are used as reference data, while the Saral/Altika and SWOT nadirs are used as independent data. Firstly, the HRET22 (High-Resolution Empirical Tide 22) internal tide atlas is used to remove the coherent internal tide from the SLA of referenced missions. Secondly, the MIOST (Multivariate Inversion of Ocean Surface Topography, Ubelmann et al.,2022) inversion method is employed to evaluate the incoherent tide in the SLA residual from the first step. Various time windows are tested to evaluate the incoherent tide. All these tests show that MIOST can capture nonstationary internal tide amplitudes between 2 and 5 cm i.e. 20–40% more variability compared to the HRET22 coherent internal tide amplitude. On independent missions, combining coherent and incoherent solutions improves the quality of the correction as shown in the Indonesian region of the Pacific.