Florent Lyard

The FES2022 Global Tide Atlas represents a significant advancement in global tidal modelling, specifically designed to meet the high-resolution tidal correction requirements of modern altimetry missions like the Surface Water and Ocean Topography (SWOT) mission, which demand enhanced resolution and accuracy in the coastal seas. Building on the success of its predecessor FES2014, which performed well in most ocean regions but exhibited residuals issues in coastal, shelf, and polar areas, FES2022 introduces a tenfold increase in mesh resolution, prioritizing coastal and shelf regions. To some extent, this resolution aligns with SWOT’s KaRIn instrument capabilities, ensuring compatibility with its high-resolution ocean elevation measurements in shallow water regions. The bathymetry dataset is a composite of GEBCO_2020 and regional patches from other datasets, with a 2-meter depth threshold to better capture shallow coastal dynamics. The underlying hydrodynamic model (T-UGOm) includes both frequency-domain and time-stepping solvers, with the latter providing more accurate schemes for non-linearities in tides. Bottom friction and wave drag parameters were regionally calibrated. The model also incorporates atmospheric forcing from ERA5 to account for the radiational component of tides when relevant. The data assimilation process uses an ensemble Kalman filter with 358 members, generated by perturbing bathymetry, bottom friction, and wave drag. 16 tidal constituents were assimilated, along with 18 additional waves derived from time-stepping simulations. The assimilation was performed in two iterations (the second one resulting in the final FES2022b atlas) to incorporate the FES2022a Loading and Self-Attraction solution, enhancing the consistency between the model and the observations. The validation of FES2022b demonstrates substantial improvements over FES2014b and other state-of-the-art models. In the frequency domain, the Root Sum Square (RSS) errors for tidal elevations were reduced to 7.6 mm at altimetry crossovers in the deep ocean, 11.3 mm on shelves, and 42.3 mm at tide gauges compared to FES2014b. Temporal validation showed a variance reduction in Sea Surface Height (SSH) of -2.26 cm² for Jason-3 and -5.75 cm² for AltiKa when compared to FES2014b, with even greater reductions (-16.6 cm² for AltiKa) when compared to GOT4.10c. In polar regions, FES2022b significantly reduced the Sentinel-3A SSH variance in the Arctic (Baffin Bay, Siberian Shelf) and Antarctic (Ross and Weddell Seas). Coastal zones benefited from more than 40 cm² of variance reduction within 20 km of the shore. Tidal current validation using 119 current-meter stations showed a 56 % improvement compared to FES2014b, with a global RMSD of 2 cm/s for the major axis of tidal ellipses. GRACE gravity field residuals were also reduced, particularly around the Vancouver Island, from 10 cm to 3 cm EWE (Equivalent Water Elevation). Despite these advancements, some local residual errors persist due to bathymetry inaccuracies, shoreline misalignments, and limited high-latitude data coverage. These issues will be addressed in the future FES release. FES2022 is operational for altimetry de-aliasing corrections and available for download on the AVISO+ website, along with the prediction code on the CNES GitHub. Future improvements will focus on integrating latest bathymetry databases, refining shoreline databases, and enhancing high-latitude coverage of data assimilation through dedicated missions. The model’s unprecedented accuracy in coastal and polar regions makes it a recommended replacement for FES2014 in operational and scientific applications.

Continental shelves challenge satellite altimetry. Over the macrotidal Argentine Continental Shelf, SWOT's unprecedented 1-day CalVal phase enables assessing the mission; using five in situ records, we present the first validation of its L3 sea surface height anomalies. KaRIn sensor noise is low, so residual accuracy is set by the corrections, not the instrument—the tides, best removed by FES2022b, and the dynamic atmospheric correction (DAC), the inverted-barometer (IB) response plus a wind-driven component. Assessing five DACs by cross-spectral coherence (2—10 day band) and isolating that dynamic component against the in situ data, we find none preserves shelf dynamics cleanly; each shifts the signal in time or alters its variance. Only under IB alone does SWOT cleanly resolve regional processes such as northward coastally trapped waves (~4.6-day period; 12.9 ± 3.5 m s ^-1 ), which every DAC degrades. For now, IB-only fields are the safer choice to preserve high-frequency shelf dynamics.

The Southwestern Tropical Pacific exhibits a complex bathymetry and represents a hot spot of internal tide generation. Based on a tailored high-resolution regional model, we investigate for the first time the internal tide field around the New Caledonia islands through energy budgets that quantify the internal tide generation, propagation, and dissipation. A total of 15.97 GW is converted from the barotropic to the baroclinic tide with the main conversion sites associated with the most prominent bathymetric structures such as continental slopes and narrow passages in the north (2.17 GW) and ridges and seamounts south of New Caledonia (3.92 GW). The bulk of baroclinic energy is generated in shallow waters around 500 m depth and on critical to supercritical slopes highlighting the limitations of linear semi-analytical models in those areas. Despite the strongly dominant mode-1 generation, more than 50 % of the locally generated energy dissipates in the near-field close to the generation sites. The remaining energy propagates within well-defined tidal beams with baroclinic energy fluxes of up to 30 kW m⁻¹ toward the open ocean, strongly dominated by mode-1. The energetic mesoscale eddy activity in the region appears to be the main source of tidal incoherence. Locally, mesoscale eddy-driven stratification changes induce variations of the conversion term. In the far-field, incoherence of the energy flux arises through the interaction of the tidal beam with the eddying background flow. The New Caledonia site represents a challenge for SWOT (Surface Water Ocean Topography) observability of meso- and submesoscale dynamics in the presence of internal tides with sea surface height signatures > 6 cm. We show that a correction of the coherent baroclinic tide may improve the observability range by shifting the transition scale between balanced and unbalanced flow in winter from 180 km to 50–80 km. In contrast, in summer observability increases only marginally due to the seasonally amplified signature of the incoherent tide at scales below 100 km.

The Southwestern Tropical Pacific exhibits a complex bathymetry and represents a hot spot of internal tide generation. Based on a tailored high-resolution regional model, we investigate for the first time the internal tide field around the New Caledonia islands through energy budgets that quantify the internal tide generation, propagation, and dissipation. A total of 15.97 GW is converted from the barotropic to the baroclinic tide with the main conversion sites associated with the most prominent bathymetric structures such as continental slopes and narrow passages in the north (2.17 GW) and ridges and seamounts south of New Caledonia (3.92 GW). The bulk of baroclinic energy is generated in shallow waters around 500 m depth and on critical to supercritical slopes highlighting the limitations of linear semi-analytical models in those areas. Despite the strongly dominant mode-1 generation, more than 50 % of the locally generated energy dissipates in the near-field close to the generation sites. The remaining energy propagates within well-defined tidal beams with baroclinic energy fluxes of up to 30 kW m⁻¹ toward the open ocean, strongly dominated by mode-1. The energetic mesoscale eddy activity in the region appears to be the main source of tidal incoherence. Locally, mesoscale eddy-driven stratification changes induce variations of the conversion term. In the far-field, incoherence of the energy flux arises through the interaction of the tidal beam with the eddying background flow. The New Caledonia site represents a challenge for SWOT (Surface Water Ocean Topography) observability of meso- and submesoscale dynamics in the presence of internal tides with sea surface height signatures > 6 cm. We show that a correction of the coherent baroclinic tide may improve the observability range by shifting the transition scale between balanced and unbalanced flow in winter from 180 km to 50–80 km. In contrast, in summer observability increases only marginally due to the seasonally amplified signature of the incoherent tide at scales below 100 km.

Thanks to its current accuracy and maturity, altimetry is considered as a fully operational observing system dedicated to various applications such as climate studies. Altimeter measurements are corrected from several geophysical parameters in order to isolate the oceanic variability and tide correction is one of the most critical. The accuracy of tidal models has been much improved for the last 25 years leading to centimetric accuracy in the open ocean. The last release of the global tidal model, referenced as FES2014b was distributed in mid-2016.The underlying unstructured mesh resolution of FES2014b was increased in areas of interest like shallow waters and on the slope of the continental shelves, and the error of the pure hydrodynamic ocean solution has been divided by a factor of 2 compared to the previous version (FES2004). Still, some significant errors remain in some regions, due to the omission of compound tides and bathymetric errors (in shelf/coastal seas), seasonal sea ice effects, and lack of available data for assimilation (in the high latitudes).To address the reduction of these errors and face the new challenges of the tide correction for HR altimetry, in particular, the forthcoming SWOT mission, a new global tide model FES2022 has been developed, focusing particularly on shallow waters and high latitudes.This new tidal solution uses higher spatial resolution in coastal areas, extending systematically the model mesh to the narrowest coastal systems (fjords, estuaries, …), and the model bathymetry has been upgraded in many places thanks to an international collaboration effort. The hydrodynamic modeling benefits also from further improvements which allow producing very accurate hydrodynamic simulations. The use of the most recent altimeter standards and high inclination altimeters like Cryosat-2, Saral/AltiKa, and even Sentinel-3, also allowed retrieving some tide observations in the highest latitudes to help improving the polar tides modeling. Results show a great improvement in the FES2022 hydrodynamic solution compared to FES2014’s one. The assimilation procedure was conducted, and a specific loading tide solution was produced. The final FES2022 tidal solution was validated in comparison to the FES2014b, EOT20, GOT, and TPXO9v5 models, for the missions Jason 3, Sentinel-3A, and Cryosat-2. Some validations of the new FES2022 tidal current are also presented here.

Ocean surface currents are critical not only to ocean dynamics, but also to marine ecosystems, maritime navigation and safety, search and rescue, monitoring and mitigation of marine pollution including oil spills, plastic, and debris. Wind-current coupling impacts both the ocean and the atmosphere, thereby influencing weather and climate. Recent modeling studies underscore the importance of submeoscale-to-mesoscale surface currents in ocean dynamics, marine ecosystems, and air-sea interactions. However, the present observing system is inadequate in observing these currents, posing major challenges in understanding their impacts. Moreover, many operational oceanography applications require measurements of these small-scale currents over the global ocean. To reduce these knowledge and capability gaps, here we present a satellite mission concept “Ocean Dynamics and Surface Exchange with the Atmosphere” (ODYSEA) that is being proposed as a NASA Earth System Explorers satellite through a strong partnership with CNES. The mission will provide the first-ever measurements of total (geostrophic+ageostrophic) surface currents in the global ocean along with simultaneous measurements of ocean-surface vector winds. ODYSEA is designed to have a 1700-km wide swath, providing approximately daily coverage of the global ocean with 5-km postings. These measurements will provide an unprecedented opportunity to unravel the physical processes underlying small-scale ocean dynamics and air-sea interactions. ODYSEA’s near real-time data will support key operational needs such as weather and ocean forecasting, search and rescue, and seafaring.

The Southwestern Tropical Pacific exhibits a complex bathymetry and represents a hot spot of internal tide generation. Based on a tailored high-resolution regional model, we investigate for the first time the internal tide field around the New Caledonia islands through energy budgets that quantify the internal tide generation, propagation, and dissipation. A total of 15.97 GW is converted from the barotropic to the baroclinic tide with the main conversion sites associated with the most prominent bathymetric structures such as continental slopes and narrow passages in the north (2.17 GW) and ridges and seamounts south of New Caledonia (3.92 GW). The bulk of baroclinic energy is generated in shallow waters around 500 m depth and on critical to supercritical slopes highlighting the limitations of linear semi-analytical models in those areas. Despite the strongly dominant mode-1 generation, more than 50 % of the locally generated energy dissipates in the near-field close to the generation sites. The remaining energy propagates within well-defined tidal beams with baroclinic energy fluxes of up to 30 kW m⁻¹ toward the open ocean, strongly dominated by mode-1. The energetic mesoscale eddy activity in the region appears to be the main source of tidal incoherence. Locally, mesoscale eddy-driven stratification changes induce variations of the conversion term. In the far-field, incoherence of the energy flux arises through the interaction of the tidal beam with the eddying background flow. The New Caledonia site represents a challenge for SWOT (Surface Water Ocean Topography) observability of meso- and submesoscale dynamics in the presence of internal tides with sea surface height signatures > 6 cm. We show that a correction of the coherent baroclinic tide may improve the observability range by shifting the transition scale between balanced and unbalanced flow in winter from 180 km to 50–80 km. In contrast, in summer observability increases only marginally due to the seasonally amplified signature of the incoherent tide at scales below 100 km.

The Southwestern Tropical Pacific exhibits a complex bathymetry and represents a hot spot of internal tide generation. Based on a tailored high-resolution regional model, we investigate for the first time the internal tide field around the New Caledonia islands through energy budgets that quantify the internal tide generation, propagation, and dissipation. A total of 15.97 GW is converted from the barotropic to the baroclinic tide with the main conversion sites associated with the most prominent bathymetric structures such as continental slopes and narrow passages in the north (2.17 GW) and ridges and seamounts south of New Caledonia (3.92 GW). The bulk of baroclinic energy is generated in shallow waters around 500 m depth and on critical to supercritical slopes highlighting the limitations of linear semi-analytical models in those areas. Despite the strongly dominant mode-1 generation, more than 50 % of the locally generated energy dissipates in the near-field close to the generation sites. The remaining energy propagates within well-defined tidal beams with baroclinic energy fluxes of up to 30 kW m⁻¹ toward the open ocean, strongly dominated by mode-1. The energetic mesoscale eddy activity in the region appears to be the main source of tidal incoherence. Locally, mesoscale eddy-driven stratification changes induce variations of the conversion term. In the far-field, incoherence of the energy flux arises through the interaction of the tidal beam with the eddying background flow. The New Caledonia site represents a challenge for SWOT (Surface Water Ocean Topography) observability of meso- and submesoscale dynamics in the presence of internal tides with sea surface height signatures > 6 cm. We show that a correction of the coherent baroclinic tide may improve the observability range by shifting the transition scale between balanced and unbalanced flow in winter from 180 km to 50–80 km. In contrast, in summer observability increases only marginally due to the seasonally amplified signature of the incoherent tide at scales below 100 km.

The Southwestern Tropical Pacific exhibits a complex bathymetry and represents a hot spot of internal tide generation. Based on a tailored high-resolution regional model, we investigate for the first time the internal tide field around the New Caledonia islands through energy budgets that quantify the internal tide generation, propagation, and dissipation. A total of 15.97 GW is converted from the barotropic to the baroclinic tide with the main conversion sites associated with the most prominent bathymetric structures such as continental slopes and narrow passages in the north (2.17 GW) and ridges and seamounts south of New Caledonia (3.92 GW). The bulk of baroclinic energy is generated in shallow waters around 500 m depth and on critical to supercritical slopes highlighting the limitations of linear semi-analytical models in those areas. Despite the strongly dominant mode-1 generation, more than 50 % of the locally generated energy dissipates in the near-field close to the generation sites. The remaining energy propagates within well-defined tidal beams with baroclinic energy fluxes of up to 30 kW m⁻¹ toward the open ocean, strongly dominated by mode-1. The energetic mesoscale eddy activity in the region appears to be the main source of tidal incoherence. Locally, mesoscale eddy-driven stratification changes induce variations of the conversion term. In the far-field, incoherence of the energy flux arises through the interaction of the tidal beam with the eddying background flow. The New Caledonia site represents a challenge for SWOT (Surface Water Ocean Topography) observability of meso- and submesoscale dynamics in the presence of internal tides with sea surface height signatures > 6 cm. We show that a correction of the coherent baroclinic tide may improve the observability range by shifting the transition scale between balanced and unbalanced flow in winter from 180 km to 50–80 km. In contrast, in summer observability increases only marginally due to the seasonally amplified signature of the incoherent tide at scales below 100 km.