Analysis of multi-decadal tide records, satellite altimetry, and high-resolution oceanic reanalysis around the Hawaiian Ridge identifies correlations between offshore and onshore mean sea level (MSL), M2 tidal amplitudes, and ocean stratification; these are linked to Pacific decadal climate variability. Empirical orthogonal function analyses reveal strongly correlated quasi-decadal variability in onshore and offshore tides and MSL, and all three factors are highly correlated with regional density stratification. This decadal variability is highly correlated with multiple Pacific climate indices, suggesting that this climate variability influences internal tides via coupled ocean-atmosphere mechanisms. The surface expression of variations in the M2 internal tide yield correlated variability between MSL and M2 offshore and onshore. The M2 signals at all tide gauges have stronger relationships to MSL in the altimetry era (1992-2023) than their respective full records, and both factors show stronger connections to climate variations in recent years. The M2 signal at Hilo is most clearly connected to climate variability over its full record, stronger even than the MSL-climate connections at all tide gauges. The amplitudes of the climate-induced tidal variations are on are on the order of 10% on top of MSL variability and long-term steric sea level rise. This amplification may exacerbate the frequency of high-tide flooding (also known as “sunny-day flooding”) in harbors and other low-lying areas of Hawai’i, highlighting the need for dynamic coastal management strategies that integrate astronomical, non-astronomical, and climatic factors, in sea level projections.

The long-wavelength correction (LWC) of SWOT data is intended to reduce errors related to the stability of the SWOT antenna and its attitude in orbit, especially those errors related to the roll of the satellite.The algorithms used to compute the LWC utilize SWOT KaRIn sea surface-height (SSH) measurements and additional data, and the LWC may abosrb geophysical SSH into the correction. Different LWC algorithms are used on the L2 and L3 SWOT products, which are analyzed here during the 1-day repeat (Cal/Val) mission phase lasting approximately 100 days. During this mission phase the SSH anomaly (SSHA) computed using the L3 LWC is much more realistic than the L2 LWC, shown here by comparing spatial statistics of the L2 and L3 products.The L3 LWC algorithm is nonlinear insofar as it depends on second-order statistics of the SSHA and multi-satellite SSHA differences, making it difficult to quantify the extent to which it could absorb baroclinic tidal signals. To overcome this difficulty, a proxy L3 LWC algorithm is developed which mimics the L3 LWC but is strictly linear in the SSHA. The proxy LWC is applied to the predicted internal tide available on the products, and it is found to absorb roughly 5% to 10% of the variance of the internal tide; although, this figure varies strongly depending on the magnitude and orientation of the tidal waves.

This study showcases a global, heterogeneously coupled total water level system wherein salinity and temperature outputs from a coarse-resolution ($\sim$12 km) ocean general circulation model are used to calculate density-driven terms within a global, high-resolution ($\sim$2.5 km) depth-averaged total water level model. We demonstrate that the inclusion of baroclinic forcing in the barotropic model requires careful treatment of the internal wave drag term in order to maintain the fidelity of tidal results from the purely barotropic model. By accurately capturing the internal tide dissipation within the coupled system, the resulting heterogeneously coupled model has deep-ocean tidal errors of 2.27 cm, outperforming global, depth-resolving ocean models in representing global tides. Moreover, global median root mean square errors as compared to observations of total water levels, 30-day sea levels, and non-tidal residuals improve by 1.86, 2.55, and 0.36 cm respectively. The drastic improvement in model performance highlights the importance of including density-driven effects within global hydrodynamic models and will help to improve the results of both hindcasts and forecasts in modeling extreme and nuisance flooding. With only an 11\% increase in computational time as compared to the fully barotropic total water level model, this efficient approach paves the way for high resolution coastal water level and flood models to be used directly alongside climate models, improving operational forecasting of total water levels.

Internal tides (ITs) in the Indonesian seas were largely investigated and hotspots of intensified mixing identified in the straits in regional models and observations. Both of them indicate strong mixing up to 10⁻⁴cm/s even close to the surface and show that tides at spring-neap cycle cool by 0.2°C the surface water at ITs’ generation sites.These findings supported the idea of strong and surfaced mixing capable of providing cold and nutrient-rich water favorable for the whole ecosystem. However, it has never been assessed through an ad-hoc study. Our aim is to provide a quantification of ITs impact on chlorophyll-a through a coupled model, whose physical part was validated against the INDOMIX data in precedent studies and the biogeochemical part is compared to in-situ samples and satellite products. In particular, explicit tides’ inclusion within the model improves the representation of chlorophyll and of the analyzed nutrients. Results from harmonic analysis of chlorophyll-a demonstrate that tidal forcing modify spring/neap tides’ variability on the regions of maximum concentration in correspondence to ITs’ génération areas and to plateau sites where barotropic tides produce large friction reaching the surface. The adoption of measured vertical diffusivities explains the biogéochemical tracers’ transformation within the Halmahera Sea and used to estimate the nutrients’ turbulent flux, with an associated increase in new production of ~25% of the total and a growth in mean chlorophyll of ~30%. Hence, we confirm the key role of ITs in shaping vertical distribution and variability of chlorophyll as well as nutrients in the maritime continent.