New Dataset based on HYCOM forecast system enhances Internal Tide corrections for SWOT Cal/Val

The internal-wave resolving (IWR) modeling team have released a valuable new dataset providing sea surface height (SSH) corrections for internal tides derived from the HYbrid Coordinate Ocean Model (HYCOM), specifically tailored for the Surface Water and Ocean Topography (SWOT) mission’s Calibration and Validation (Cal/Val) phase. This resource, which accounts for both phase-locked and non-phase-locked internal tide components, promises to refine the accuracy of satellite altimetry data and advance our understanding of ocean dynamics.

Internal tides—subsurface waves generated by tidal flows interacting with underwater topography—produce detectable SSH signals that can obscure non-tidal ocean features like mesoscale eddies. The SWOT mission, launched in December 2022, aims to map these features with unprecedented resolution, but accurate separation of tidal from non-tidal signals is essential. Traditional models like the High-Resolution Empirical Tide model (HRET) effectively capture only the predictable, phase-locked portion of internal tides. This new HYCOM-based dataset goes further by incorporating the variable, non-phase-locked components, offering a more comprehensive correction tool.

Developed as part of ongoing efforts under the National Oceanographic Partnership Program’s Global Internal Waves (NOPP GIW) initiative, the dataset draws from a data-assimilative HYCOM forecast system evaluated during the SWOT Cal/Val period. Accompanying research, detailed in a preprint manuscript titled “Advancing Internal Tide Correction for SWOT Cal/Val: The Role of Ocean Forecasts” (DOI: 10.22541/essoar.174164232.20506498/v2), demonstrates HYCOM’s superior performance. Led by Badarvada Yadidya from the University of Michigan, along with collaborators from the Naval Research Laboratory, Oregon State University, the University of Southern Mississippi, and Collecte Localisation Satellites SA, the study shows that HYCOM reduces phase-locked internal tide variance by an average of 5% more than HRET. Overall, it achieves a 24.6% greater total variance reduction by addressing non-phase-locked tides. At the dominant M2 tidal frequency, HYCOM can mitigate up to 73% of total internal tide variance in SWOT observations.

The dataset is publicly available through Harvard Dataverse at https://doi.org/10.7910/DVN/QQUQNZ. It includes gridded SSH anomaly fields on the 2-km SWOT swath grid, enabling researchers to apply tide corrections directly to SWOT data. Users can download NetCDF files covering the Cal/Val region. Note: If internal tide correction is already applied in the SWOT product you are using (typically based on the HRET model), you must first add the default HRET phase-locked internal tide signal back into the SSH field before applying the HYCOM correction. This step ensures the total (phase-locked + non-phase-locked) internal tide signal is properly removed using the comprehensive HYCOM fields.

This release underscores the NOPP GIW program’s commitment to bridging observational and modeling frontiers in internal wave research. As SWOT data continues to pour in, tools like this HYCOM dataset will be instrumental in realizing the mission’s full potential. For more on the supporting research, visit the preprint at https://doi.org/10.22541/essoar.174164232.20506498/v2.