We invite contributions on oceanic energy pathways and their consistent representation in numerical models from theoretical, modeling, and observational perspectives. These include, but are not limited to, the processes involving mesoscale eddies, internal gravity waves, instabilities, turbulence, small-scale mixing, and ocean-atmosphere coupling. Contributions on energy transfer processes and their quantification from in-situ measurements, (semi-)analytical approaches, and numerical models, as well as their parameterizations and spurious energy transfers associated with numerical discretizations, are also welcome along with interdisciplinary contributions such as novel applications in data science that diagnose, quantify, and minimize energetic inconsistencies and related uncertainties.
We particularly encourage early career researchers to participate in this session.
Orals: Thu, 7 May, 14:00–15:45 | Room L3
The ocean is forced at large scales by fluxes of momentum and buoyancy. Yet, climate equilibrium can only be reached through the dissipation of these energy sources, which occur at much smaller scales. Understanding how energy is transferred across this wide range of scales and the routes to dissipation are therefore key to understand the ocean response to future climate scenarios and remains a central challenge in physical oceanography. While the inverse kinetic energy cascade associated with geostrophic turbulence has been extensively studied, the direct cascade of kinetic energy and the processes that enable energy transfer towards dissipative scales remain incompletely understood and poorly constrained in global ocean models.
In this talk, we review some of the recent work achieved in identifying and quantifying the processes leading to cross-scale energy fluxes using flow decomposition methods and spectral fluxes analyses, applied to realistic high-resolution simulations forced with eddies and internal waves. We show how the interaction between eddies and internal waves are central in enhancing the direct energy cascade –as opposed to the common paradigm relying on interactions among internal waves–, and in reducing the inverse energy cascade. We describe as well the physical processes underlying these interactions.
These studies establish eddy–internal wave interactions as a fundamental component of the ocean energy budget, with implications for mixing, dissipation, and the parameterization of sub grid scale processes in ocean models.
How to cite: Delpech, A.: Eddy-internal waves interactions and their contribution to cross-scale energy transfers in the ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17830, https://doi.org/10.5194/egusphere-egu26-17830, 2026.
Ocean submesoscale eddies, characterized by horizontal scales less than the first baroclinic Rossby radius of deformation, are increasingly recognized for their critical roles in marine ecosystems, ocean energy balance, and the Earth’s climate system. Despite extensive research on these submesoscale features through high-resolution simulations and regional observations, our knowledge of their dominant driving mechanism from a global perspective is very limited. Here, we present the global observational evidence for the primary role of mesoscale Lagrangian coherent structures (LCSs) in driving submesoscale eddy generation by synergic application of high-resolution spaceborne synthetic aperture radar data and radar altimeter data. Applying a deep-learning detection system to more than three million global Sentinel-1 and Envisat SAR images, we found that more than 80% of detected submesoscale eddies are clustered within a 10-km range around mesoscale LCSs characterized by high kinetic energy and persistent straining. Further composition analysis quantifies that more than half of submesoscale eddies occur within the ring-shaped areas of coherent mesoscale eddies, where the strong strain is conducive to frontogenesis. Our findings highlight that the generation of submesoscale eddies is attributed to instabilities initiated by strain-induced frontogenesis. This study establishes a new paradigm for locating submesoscales by targeting LCSs, thereby supporting a global evaluation of their contributions to energy balance and material transport.
How to cite: Zi, N., Li, X.-M., and Gade, M.: Ocean mesoscale coherent structures dominate the generation of global submesoscale eddies, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-516, https://doi.org/10.5194/egusphere-egu26-516, 2026.
The southern coast of Korea is characterized by a complex Rias coast and a barotropic flow regime dominated by strong tides. Under the influence of tidal forcing, complex current patterns develop regularly, leading to the generation of coastal eddies with spatial scales ranging from 0.1 to 10 km. These submesoscale eddies serve as an intermediary between mesoscale dynamics and small-scale turbulence, playing an important role in energy transfer. The goal of this study is to understand the dynamics of eddies observed during a field campaign near the Yokji region and Nodae Island using an eddy-resolving numerical model (with a grid resolution of 30 m). A numerical hydrodynamic model for the region was developed by the Deflt3D model and validated using Acoustic Wave and Current profiler data, velocity fields estimated from unmanned aerial vehicle imagery, and Sentinel-2 true-color imagery. To characterize eddy generation and interaction processes, the barotropic vorticity diagnostics for the depth-integrated flow are used. The local dynamics of submesoscale eddies highlight that the nonlinear advection is the leading local source of vorticity over the study area, followed by secondary contributions from bottom pressure torque and bottom drag curls interacting with topography. We employed a coarse-graining approach to estimate multiscale energy fluxes and kinetic energy transfer. The analysis suggests a tendency for localized upscale energy transfer into adjacent larger-scale background current during the eddy dissipation phase, and that barotropic instability near the cape is a potential contributor to the observed eddy generation. This framework will offer broader applicability for understanding submesoscale energetics and instability processes in tidally dominated shallow coastal systems.
How to cite: Kim, S.-Y., Choi, J.-G., and Jo, Y.-H.: Submesoscale Eddy Dynamics and Energy Transfer in a Tidally Dominated Coastal System, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9204, https://doi.org/10.5194/egusphere-egu26-9204, 2026.
Global ocean models at resolutions that do not resolve mesoscale eddies lack variability, not just on scales that they cannot represent because they are below the grid scale, but also on resolvable scales. This research develops a backscatter parameterizations that increases variability on the resolved scales of a non-eddying model. The parameterization acts on the model's momentum equations, and sets the rate of backscatter, viz. the rate at which energy is injected to the resolved scales, proportional to the rate at which the Gent-McWilliams (GM) parameterization removes energy from the resolved scales. This models the physical process whereby mesoscales convert large-scale potential energy to kinetic energy, and then transfer that kinetic energy towards larger scales. These parameterization is implemented in the MOM6 ocean model, and results are presented on its impact in simulations at nominal 2/3-degree resolution. Stochastic GM+E acts primarily in the Southern Ocean, the North Atlantic Current, and the Kuroshio Extension, where it impacts SST variability and southern-hemisphere sea ice extent.
How to cite: Grooms, I., Agarwal, N., Marques, G., Pegion, P., and Yassin, H.: Stochastic GM+E: An energetically-informed stochastic backscatter scheme for ocean models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14014, https://doi.org/10.5194/egusphere-egu26-14014, 2026.
Turbulent mixing plays a key role in regulating heat and salt distribution in polar oceans, influencing water-mass transformation and ice-ocean interactions, yet direct observations of mixing south of 60°S remain scarce. As a result, the magnitude and drivers of vertical mixing in the Southern Ocean, particularly under and near sea ice, remain poorly constrained. Here, we present microstructure turbulence observations collected over three consecutive austral summers (2023-2025) in the King Haakon VII Sea (the eastern part of the Weddell Gyre, Southern Ocean). We observe enhanced sub-surface mixing over the continental slope, with mean dissipation rates an order of magnitude higher than typical values in the open ocean below the mixed layer.
This elevated mean dissipation on the continental slope is strongly influenced by a single episodic extreme event, reaching dissipation rates of up to 3 × 10⁻⁶ W kg⁻¹ mid-depth. Excluding the extreme event, we still observe enhanced mixing on the slope, with mean dissipation about three times higher than the open ocean values below the mixed layer. The observed elevated dissipation is associated with peaks in velocity shear and occurs when tidal inversion models predict periods of large tidal acceleration during the spring-tide cycle. Comparisons with internal-tide mixing model outputs further suggest that the enhanced slope mixing is driven by tides interacting with the steep continental slope.
Based on our observations, the continental slope mixing acting on the local temperature gradients produces a mean upward heat flux of approximately 3 W m⁻² into the base of the Winter Water layer, with peak values of 10 W m⁻². The extreme mixing event occurred within the Winter Water itself, where temperature gradients are weak. However, if the same extreme turbulence were to occur on the stronger thermal gradients at the base of the Winter Water layer, it could generate vertical heat fluxes of up to 124 W m⁻² from the underlying warm waters into the Winter Water layer.
Model-based estimates further suggest that tidal mixing along the Antarctic continental slope could drive a circumpolar mean heat flux of approximately 9 W m⁻² into the base of the Winter Water. These results highlight continental slope mixing as a mechanism for upper-ocean heat redistribution, with implications for Antarctic sea-ice formation, melt processes, and polar ocean heat budgets more broadly.
How to cite: Hus, J. J., Meyer, A., Hattermann, T., Peña-Molino, B., and de Lavergne, C.: Observed Enhanced Mid-Depth Mixing on the Antarctic Continental Slope Drives Heat Flux Into the Winter Water Layer., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16047, https://doi.org/10.5194/egusphere-egu26-16047, 2026.
Oceanic energy budgets and mixing parameterizations are largely framed around tidal forcing, reflecting the availability of long-term, global datasets for barotropic and baroclinic tides. In contrast, internal waves, particularly Internal Solitary Waves (ISWs), remain poorly represented in global energy frameworks, despite their recognized role in transferring energy across scales, driving localized mixing, and modulating stratification. This imbalance is not only conceptual but observational: the lack of consistent, global datasets has limited the integration of internal wave processes into large-scale circulation and climate-relevant ocean models.
ISWs are nonlinear internal waves that propagate over long distances in stratified oceans, linking mesoscale and large-scale forcing to small-scale turbulence. Beyond their surface expressions observable from space, ISWs involve strong internal currents and large vertical displacements of isopycnals, with implications for offshore operations, marine structures, navigation, and ocean energetics. However, their transient nature and wide spatial extent make them particularly challenging to observe systematically, resulting in fragmented and geographically biased observational records.
We present the Internal Waves Service (IWS), which provides a first step towards addressing this gap, as a global, open, service-oriented framework for the systematic detection, mapping, and archiving of ISWs from satellite Earth Observation data. The service currently exploits synthetic aperture radar (SAR) imagery acquired by Sentinel-1 in Wave Mode, which provides unique, globally distributed observations of ISW surface signatures. Unlike traditional studies focused on specific regions or short time periods, the IWS processes all Sentinel-1 Wave Mode acquisitions on a continuous basis, enabling consistent global mapping of ISW presence and absence.
ISW detection is performed using an AI-assisted classification framework applied to SAR vignettes, supported by expert validation and iterative model refinement. The resulting products form a persistent, standardized dataset documenting spatial patterns and temporal variability of ISW activity across ocean basins.
By consolidating previously fragmented observations into a coordinated global dataset, the IWS provides a new observational basis for assessing the role of internal waves within ocean energy pathways. This systematic mapping supports comparative analyses, facilitates model evaluation, and opens the door to more consistent integration of internal wave processes alongside tides in multiscale ocean dynamics and energy budgets. Developed as a community-driven initiative involving 24 research institutions across 12 countries, the IWS is designed to evolve towards broader sensor integration and enhanced spatial coverage, strengthening its relevance for ocean modelling and climate studies.
How to cite: Santos-Ferreira, A., Pinelo, J., da Silva, J. C. B., Johannessen, J. A., Magalhaes, J. M., Forget, G., Gonçalves, J., Chapron, B., Gommenginger, C., Pinheiro, M., Carr, M., Buijsman, M., Oikonomoy, E., Stastna, M., Shutler, J., Pineda, J., Terletska, K., Hartharn-Evans, S., Holt, B., and Collard, F. and the Internal Waves Service (IWS) Consortium: Internal Waves Service: Towards Systematic Global Observation of Internal Solitary Waves, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14433, https://doi.org/10.5194/egusphere-egu26-14433, 2026.
Internal tides (ITs) play a fundamental role in ocean dynamics by transferring tidal energy through cascades to small-scale turbulence, ultimately driving diapycnal mixing that sustains the deep-ocean circulation and regulates biogeochemical cycles. While ITs energy sinks are traditionally attributed to topographic interactions, the impact of surface wind forcing on this energy pathway remains a significant area of uncertainty. To address this knowledge gap, this study employs a dynamical decomposition approach applied to realistic ITs-resolving numerical simulations to quantify the wind impact on ITs in the global ocean. Our analysis reveals that wind forcing globally imposes a strong damping effect on ITs, with a median magnitude of the wind work on ITs of O (10-4) W/m². Globally, this wind damping accounts for a non-negligible fraction of the total ITs energy sink, substantially influencing the distributions of ITs and the diapycnal mixing they induce. To provide observational constraints beyond numerical simulations, we develop a scaling approach to estimate wind damping of ITs by projecting the ITs velocity onto the wind direction and evaluating the net wind work over a tidal cycle. Our findings collectively suggest that wind damping constitutes a critical component of the ITs energy budget. This challenges the conventional paradigm of predominantly topography-driven energy sinks and underscores the necessity of integrating atmospheric forcing into a holistic understanding of ITs energy budget.
How to cite: Liu, Y., Liu, Z., Wang, D., and Wang, C.: Wind Damping of Internal Tides in the Global Ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3315, https://doi.org/10.5194/egusphere-egu26-3315, 2026.
Interferometric missions such as SWOT, together with conventional nadir altimetry missions, provide unprecedented observations of sea surface height variability relevant to climate studies. However, the accurate exploitation of these measurements requires the correction of high-frequency signals associated with wind- and gravity-driven processes, among which internal tides and internal solitary waves represent a significant source of variability. Internal tides, also referred to as baroclinic tides, are internal gravity waves that oscillate at tidal frequencies in the ocean interior and produce sea surface height signatures of a few centimeters. For the first vertical mode, internal tides typically exhibit horizontal wavelengths ranging from about 50 to 250 km, while higher modes are characterized by smaller spatial scales. As internal tides propagate, they may lose phase coherence and undergo nonlinear steepening, resulting in organized packets of internal solitary waves with typical horizontal scales of 1–15 km, which are clearly resolved and observed by the high spatial resolution of SWOT.
Previous studies have demonstrated that global internal tide (IT) atlases are effective at correcting the stationary component of internal tide signals in altimetric observations (Carrère et al., 2021). In this study, we evaluate the performance of three recent global IT atlases—HRET22 (Zaron, 2024), ZHAO30yr (Zhao, 2025), and MIOST-IT24 (Tchilibou et al., 2025)—for the removal of stationary internal tide variability in SWOT and conventional nadir altimetry measurements.
Our results show that these atlases reduce up to approximately 20% of sea level anomaly (SLA) variance at horizontal scales between 50 and 200 km. At the global scale, MIOST-IT24 generally outperforms HRET22, while ZHAO30yr exhibits the best performance in specific regions, notably the eastern Pacific, the Atlantic Ocean, and the northern Madagascar region.
However, these global internal tide models have little to no impact at spatial scales below 50 km, which are primarily associated with higher vertical modes and internal solitary waves. This limitation highlights the need for the oceanographic community to develop new correction strategies and methodologies capable of addressing small-scale and nonlinear internal wave signals, including solitons, in high-resolution altimetric observations.
How to cite: Carrere, L., Tchilibou, M., Dabat, M.-L., Lyard, F., Ubelmann, C., and Dibarboure, G.: Use of new baroclinic tide models to improve the correction of internal tides in SWOT and nadir altimeter data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12490, https://doi.org/10.5194/egusphere-egu26-12490, 2026.
In global ocean circulation and climate models, the bottom-enhanced turbulent mixing is often parameterized by assuming that the vertical decay scale of the energy dissipation rate ζ is universally constant at 500 m. In this study, using a non-hydrostatic two-dimensional numerical model in the horizontal-vertical plane that incorporates a monochromatic sinusoidal seafloor topography and the Garrett-Munk (GM) background internal wave field, we find that ζ of the internal lee wave-driven bottom-enhanced mixing is actually variable depending on the magnitude of the steady flow U0, the horizontal wavenumber kH, and the height hT of the seafloor topography. When the steepness parameter (Sp=NhT/U0: N is the background buoyancy frequency near the seafloor) is less than 0.3, internal lee waves propagate upward from the seafloor while interacting with the GM background internal wave field to create a turbulent mixing region with ζ that extends further upward from the seafloor as U0 increases, but is nearly independent of kH. In contrast, when Sp exceeds 0.3, the inertial oscillations (IOs) gradually develop at heights not far above the seafloor topography, inhibiting the upward propagation of the bottom-generated internal lee waves. By interacting with the background IOs, the upward propagating internal lee waves dissipate some of their energy, but simultaneously contribute the rest of their energy to amplify the IOs. The oscillatory flow, consisting of the superposition of the steady flow and the IOs, efficiently generates upward propagating internal lee waves during the period centered on the time of its maximum, when it becomes transiently stationary.
How to cite: He, Y. and Hibiya, T.: The vertical structure of internal lee wave-driven benthic mixing hotspots, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2202, https://doi.org/10.5194/egusphere-egu26-2202, 2026.
Posters on site: Thu, 7 May, 10:45–12:30 | Hall X4
The Arabian Gulf (also referred to as the Persian Gulf) can exhibit energetic mesoscale dynamics despite its semi enclosed geometry. Using the GLORYS12V1 ocean reanalysis (1993–2020), this study assesses longterm patterns in sea surface height (SSH) variability and the dominant forces shaping them. The results reveal two persistent low SSH systems: one located in the northwestern part of the basin and the other in the southern Gulf. These features act as focal points of mesoscale circulation. Both systems intensify during the summer season, when atmospheric forcing and surface buoyancy losses are strongest. Their locations coincide with regions of enhanced mixing and surface cooling, suggesting a possible role in the Gulf deep water formation.
Seasonal circulation analysis indicates a summer cyclonic regime influenced by the Iranian coastal current and the Gulf coastal current, which interact with and modulate the two eddies. SSH and Eddy Kinetic Energy (EKE) fields display interannual alternation in the dominance of each eddy, highlighting their unequal sensitivity to regional dynamical conditions and basin-scale climate variability. Three dominant modes were identified using Empirical Orthogonal Function (EOF) analysis: a basin wide meridional gradient (EOF1), a two eddy dipolar mode linked to wind variability (EOF2), and southern eddy mode (EOF3) associated with the Indian Ocean Dipole Mode Index (DMI). Together, these modes describe a recurring low-frequency exchange of energy between the northern and southern eddies.
How to cite: Alrushaid, T. and Al Senafi, F.: A Dynamic Dipole: Longterm Mesoscale Oscillation in the Arabian Gulf, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-766, https://doi.org/10.5194/egusphere-egu26-766, 2026.
Observational data are fundamental for understanding geophysical dynamics, yet constraints such as cost or environmental conditions often result in sparse and noisy data. Recovering physical quantities such as energy spectra from such data constitutes a classic ill-posed inverse problem. Traditional approaches typically rely on interpolation to regular grids, which can introduce errors, especially for shallow spectra.
This study proposes a random recovery framework that infers spectra from the second-order statistics of observations under suitable assumptions. Observation noise is reduced using the Best Linear Unbiased Estimator (BLUE), while shrinkage techniques are employed to obtain stable and invertible covariance estimates under limited sampling. To achieve robust solutions without interpolation, we introduce a high-order L2 regularization, using the discrepancy principle to determine the optimal regularization parameter. For high-dimensional settings, we apply hard clustering to group similar spectra, thereby reducing the number of unknowns and enhancing recovery efficiency.
Numerical experiments demonstrate that this method offers a robust and practical approach for spectral recovery without interpolation, making it particularly suitable for sparse and noisy observations.
How to cite: Liang, H., Jäger, J., Kutsenko, A., and Oliver, M.: Interpolation-free method to recover spectra from sparse observations of random fields, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3458, https://doi.org/10.5194/egusphere-egu26-3458, 2026.
Internal solitary waves (ISWs) are widely distributed in marginal sea areas. When propagating over steep and complex continental slopes and shelves, ISWs will undergo deformation and breaking, thereby enhancing vertical mixing and energy transfer in the inner ocean and playing an important role in Earth’s biogeochemical cycles. In marginal seas, basin-scale topography not only influences the along-propagation direction evolution of ISWs, but also affects their transverse diffraction, leading to asymmetric structures along the basin axis observed in satellite imagery.
In this work, a theoretical model based on the variable-coefficient Kadomtsev-Petviashvili (vKP) equation is developed to reveal the influence of continental slopes within basin topography on the transverse diffraction of ISWs, and to explain the mechanisms governing the 2+1-dimensional propagation and evolution of ISWs over the slopes of the Sulu Sea. Using the climatological annual-mean density and bathymetry of the Sulu Sea, two idealized configurations are constructed in which topographic variations are isolated to either the along-propagation direction or the cross-propagation direction. The results show that all the dynamical coefficients vary most significantly over the slope region with water depths between 300-3000 m.
Numerical simulations of the vKP model indicate that cross-propagation direction slope variations play a dominant role in shaping the two-dimensional spatial distribution of ISWs. The asymmetric distribution of ISWs along the basin axis is primarily caused by phase speed differences induced by depth variations. In contrast, both the along- and cross-propagation directions slope variations influence the waveform evolution of ISWs. Enhanced nonlinearity in shallower regions leads to waveform steepening and larger amplitudes, whereas weaker nonlinearity and reduced amplitudes are found on the deeper side.
Furthermore, based on the simulation results, the spatial distributions of ISW energy and energy flux in the Sulu Sea are estimated. Although ISWs on the deeper side exhibit smaller amplitudes, their energy flux is significantly stronger, reaching approximately 10 kW/m, which is twice the flux on the shallow side.
How to cite: Ruan, X.: Influence Mechanism of Continental Slope on the 2D Propagation and Evolution of Internal Solitary Waves, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11738, https://doi.org/10.5194/egusphere-egu26-11738, 2026.
We analyze barotropic and baroclinic instabilities of axisymmetric vortices in a hierarchy of quasigeostrophic models. Revisiting the classical vortex profiles of Carton and McWilliams (1989), we show that these simple vortex profiles possess very low-dimensional unstable manifolds in the nondissipative limit. Using numerical simulations of the potential vorticity together with analytical calculations, we construct systematic approximations of these unstable manifolds. We then derive reduced-order models using the theory of extended normal forms on the low-dimensional reduced dynamics on these manifolds. The resulting Stuart–Landau–type amplitude equations, obtained in both data-driven and equation-driven settings, capture growth rates, frequencies, and the early nonlinear evolution leading to vortex deformation and breakup. This yields an interpretable and low-dimensional predictive description of the dynamics of vortex instabilities.
How to cite: Kaszas, B. and Thomas, L. N.: Low-Dimensional Invariant-Manifold Models of Vortex Instability , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15715, https://doi.org/10.5194/egusphere-egu26-15715, 2026.
The dynamic processes that generate a continuous oceanic energy spectrum remain poorly understood. We investigate the relative roles of tides, mesoscale eddies, high-frequency winds, and nonlinear interactions using a submesoscale-resolving ICON simulation of the South Atlantic, which captures substantially more ocean variability than conventional eddy-resolving models. Model realism is demonstrated by comparing simulated energy spectra with observations from a dedicated field campaign and satellite data. Sensitivity experiments isolate individual processes, including simulations without tidal forcing to suppress tidal waves, without high-frequency winds to suppress near-inertial waves and without mesoscale eddies to reduce wave–mean-flow interactions. Frequency–wavenumber spectra are used to distinguish random variability from wave-driven variability by identifying elevated energy along the first modes of the dispersion relation. We find that tides and high resolution are essential to reproduce realistic energy levels in the internal wave band. Suppressing near-inertial waves reduces energy between tidal peaks while enhancing energy at the peaks, highlighting the importance of wave–wave interactions in sustaining a continuous spectrum. In contrast, suppressing mesoscale eddies has a weaker effect, suggesting that wave–mean-flow interactions play a less significant role.
How to cite: Epke, M. and Brüggemann, N.: Drivers of the Continuous Oceanic Energy Spectrum at High Frequencies: A realistic modeling approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21105, https://doi.org/10.5194/egusphere-egu26-21105, 2026.
Within the scope of the international project NA-VICE, an oceanographic campaign was conducted from the Azores to Iceland in the summer of 2012. During this campaign, a Mediterranean Water Eddy (meddy) was identified at 41.3ºN, 27.1ºW. Meddies are deep subsurface anticyclones containing anomalously warm, saline modified Mediterranean Water. Generated at the topographically trapped Mediterranean Undercurrent, they can transport salt and heat great distances from the eastern boundary, accounting for at least half of the Mediterranean Water salt flux into the North Atlantic. Despite their significant role in forming the Atlantic intermediate water masses, their life cycle remains poorly understood. In this study, a meddy was identified using vertical CTD casts and ADCP data. Its core was located between 900 and 1100 m and was characterized by a salinity anomaly of 0.26, a temperature anomaly of 2.4 °C, and a negative anomaly in the buoyancy frequency. Tracing the meddy via its sea-surface manifestation and an Argo float suggests that it originated on the Irish continental slope and moved southwest toward the Mid-Atlantic Ridge. The existence of meddy generation sites well north of the Iberian Peninsula, not listed in recent studies, implies that meddies’ contribution to the heat and salt budget of the North Atlantic mid-depths might be underestimated. The detailed ADCP observations during the cruise suggest that, at that time, the meddy was interacting with a strong surface cyclone, which trapped a portion of the Mediterranean Water from the meddy, thus contributing to its decay. Future studies should investigate the additional contribution of meddies generated north of the Iberian Peninsula to the thermohaline balance of the interior North Atlantic.
How to cite: Serpa, T., Bashmachnikov, I., Relvas, P., and Martins, A.: A Northern Meddy at the Mid-Atlantic Ridge, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7682, https://doi.org/10.5194/egusphere-egu26-7682, 2026.
Internal Solitary Waves (ISW) are fundamental components of coastal ocean dynamics, playing a pivotal role in sediment transport, nutrient mixing, and the dissipation of tidal energy. These non-linear oscillations, driven by gravitational forces within stratified water columns, manifest on the ocean surface as curvilinear bands of varying roughness. This modulation of surface roughness makes them detectable by Synthetic Aperture Radar (SAR) sensors despite their negligible slope on the surface. However, while SAR offers high-resolution, all-weather monitoring capabilities, the automated quantification of ISW characteristics remains a complex challenge. Difficulties arise not only from signal contamination by atmospheric and oceanic features such as wind and rainfall, but also from the high geometric variability of the wavefronts themselves.
We propose a comprehensive analytical framework for detecting, segmenting, and characterizing internal waves using Sentinel-1 SAR observations. The methodology is developed and tested on a dataset of Level-1 Ground Range Detected Interferometric Wide Swath (GRD IW) images acquired along the northeast coast of South America. This region is oceanographically unique due to the intense stratification induced by massive coastal river discharge, specifically from the Orinoco and the Amazon rivers.
Our approach employs a two-stage process that synergizes deep learning with geometric modeling. In the first stage, a U-Net architecture segment the observation into two classes: the wave packets and the specific leading waves. The model is trained to predict a distance map relative to the feature boundaries rather than a simple binary mask. This pixel-wise regression, performed at a resolution of 50 m/px, is validated against manual annotations, providing a robust identification capability where no comparable high-resolution groundtruth exists.
Following segmentation, the second stage focuses on physical characterization. The leading wave of each detected packet is modeled using an adaptive polynomial function. Optimized via gradient descent, this function fits the curvilinear shape of the wavefront. This mathematical representation allows for the precise computation of wave orientation and propagation direction. Subsequently, the wave packet is projected onto a geometry orthogonal to the leading wave to obtain a curvature-independant representation of the wave packet. A Fourier Transform is applied to this projection to calculate the dominant wavelength. Furthermore, by analyzing the spacing and propagation direction, deducing the generation chronology of successive packets produced by tidal cycles.
Results demonstrate strong agreement between automated detections and regional dynamics. The spatial distribution reveal detection in the vicinity of . In the vicinity of Trinidad and Tobago, the spatial distribution highlights generation hotspots northwest of straits and continental shelf. Activity peaks during the autumn months, coinciding with the maximum discharge of the Orinoco River, inline with a strong modulation by stratification stability. Statistical analysis reveals a mode wavelength of approximately 350 meters, but is biased by the manual segmentation dataset. While challenges remain regarding overlapping wave fields, this tool provides a robust pathway for monitoring internal wave energetics, offering significant potential for synergy with altimetry missions, such as SWOT, and in-situ coastal management.
How to cite: Colin, A. and Husson, R.: Internal Solitary Waves characterization on Sentinel-1 observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19271, https://doi.org/10.5194/egusphere-egu26-19271, 2026.
Two-dimensional (2D) estimates of the upper-ocean vertical velocity w have been commonly performed based on single hydrographic distance–depth sections. However, biases of these estimates have seldom been investigated. We conduct such an investigation employing a 2-month dataset (including temperature, salinity, and horizontal velocity) at a typical front, the Almeria–Oran Front in the Mediterranean Sea, which was collected by a glider fleet piloted in parallel across-front sections. Specifically, using daily objective maps constructed from the dataset, we perform three-dimensional (3D) and 2D estimates of the balanced w (w3D and w2D) through the quasigeostrophic omega equation and evaluate w2D against w3D justified previously. Results show a significantly biased w2D that is estimated assuming a straight front without curvature. Generally, in the 400-m upper ocean, w2D and w3D have a weak spatial correlation of 0.4–0.6; w2D also presents a notably different magnitude, less than 50% of w3D (even less than 20% in many cases). We find a pronounced curvature-induced shearing deformation (of horizontal density gradients by geostrophic flows) effect destroying the geostrophic balance and so is the associated w to restore the balance; precluding this effect in w2D leads to the biases. These biases are also analyzed using the potential vorticity conservation principle: As the curvature causes the across-section vorticity advection, water parcels advected by the across-section flow change their vorticity; they have to be vertically compressed/stretched, requiring w that is neglected in w2D. Therefore, the biased w2D may be insufficient for understanding the vertical heat transport and its impact on the climate system.
How to cite: Liu, L., Jing, Z., and Xue, H.: Revisiting the Two-Dimensional Estimate of Ocean Vertical Velocity Using Underwater Glider Fleet Observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2681, https://doi.org/10.5194/egusphere-egu26-2681, 2026.
The multifaceted role of oceanic mesoscale eddies in the coupled climate system remains a focus of scientific discussion and research. In this study, we present a set of simulations utilizing the same model and resolution to disentangle the role of mesoscale eddies for global and local climate by applying an eddy backscatter parameterization to enhance or suppress eddy variability.
Mesoscale eddies can be seen as the oceanic high- and low-pressure systems, acting as drivers of ocean weather by introducing chaotic small-scale features into the large-scale flow. By redistributing heat, momentum, and tracers such as nutrients or dissolved trace gases, they influence and shape ocean circulation patterns and affect marine productivity through vertical mixing. Eddies also interact with the atmosphere, modulating heat and moisture exchange, which contributes to variations in wind patterns, storm tracks, and ultimately influences regional and global climate dynamics.
In this study, we conduct three distinct sets of ensemble simulations using the AWI-CM3 climate model to investigate the impact of ocean weather on climate variability. All configurations use the same spatial resolution but different levels of eddy activity due to different parameterization calibrations. One configuration is largely resolving the eddy variability, one simulation is substantially suppressing it and a reference configuration is somewhere in between using standard model parameters for AWI-CM3. With a resolution of 30 km in the atmosphere and 10–60 km in the ocean, these simulations are sufficiently detailed at the coupling interface to directly resolve air-sea interactions at the feature level. The ensemble simulations span the period from 1950 to 2015. They are then used to study the effect of eddy activity on long-term variability in large-scale ocean and atmospheric dynamics. A special focus is on mesoscale atmosphere-ocean interactions along eddy active regions such as the western boundary currents, highlighting substantial changes in local heat fluxes as well as large-scale dynamics, both in terms of climatic means and temporal variability and including changes in, e.g., Gulf Stream position and strength and its consequences for the atmospheric circulation.
How to cite: Juricke, S. and Hutter, N.: Ocean eddies in the climate system: Disentangling the role of mesoscale eddies in atmosphere-ocean interactions and global climate variability, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10743, https://doi.org/10.5194/egusphere-egu26-10743, 2026.
Ocean mesoscale eddies are ubiquitous features of the open ocean and strongly influence the ocean’s physics, chemistry, and biology. Mesoscale eddies play a critical role in the climate system and regulating the exchange of heat and carbon with the atmosphere. They also play a significant role in the redistribution of heat, salt, carbon, and nutrients around the ocean. Thus, proper modeling of eddies in both historical and future climates is crucial to accurately capturing the Earth system. Climate projections using global coupled models with eddy ocean components have recently started to become more widely used. Despite their critical role in understanding and forecasting climate characteristics, these so-called eddy-permitting models have not been rigorously explored to verify that resolved eddies are realistic, and thus any downstream scientific testing of hypotheses in biogeochemistry, ocean physics or other associated Earth systems impacted by eddies hinge on this critical assumption. This presentation compares the characteristics and behavior of observed eddies in ¼ degree satellite altimetry data with eddies detected in ¼ degree reanalysis data and ocean model output.
When compared to eddies observed in satellite altimetry data, eddies in reanalysis data and ocean model output are missing almost 30% of the number of eddy trajectories. Further, many characteristics of eddies in reanalysis data and ocean model output differ from eddies observed in altimetry data. At a high level, eddies in reanalysis data and ocean model output generally live longer, are larger, and are weaker than observed eddies in satellite altimetry data. These comparisons are made both locally and in the global aggregate to assess the differences in both the global distribution of eddy characteristics as well as differences in the regional eddy behavior.
How to cite: Lombardi, B., Grooms, I., and Kleiber, W.: Mesoscale Eddy Verification in an Eddy-Permitting Ocean Models and Reanalysis Data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13777, https://doi.org/10.5194/egusphere-egu26-13777, 2026.
Western boundary undercurrents (WBUCs), present beneath almost all western boundary currents, are significant for transporting subsurface mass and energy and connecting regional circulations. Observations suggest that WBUCs can have strong ageostrophy and intra-seasonal variability, but many dynamic details remain unclear. Here, we analyze a representative model idealized from the Kuroshio Current and Luzon Undercurrent (KC and LUC); other instances like the Gulf Stream and the Deep Western Boundary Current are also feasible. A cross-shore mean flow section, extracted from realistic simulations, serves as the only input. We employ biglobal instability analysis (BIA) and high-resolution (up to 500m) regional simulations to reveal the nonlinear instability of the WBUC, its interaction with the upper-layer, and the induced mesoscale and submesoscale turbulence. First, we solidly verify BIA by showing that the predicted evolution of dominant eigenmodes closely agrees with the model results. Second, an upper-layer (depth < 500m) KC mode and a middle-layer (500 to 1500m) LUC mode are identified. The nonlinear instability of the KC mode leads to strong variability and periodic reversal of the LUC. The subthermocline-eddy-like LUC mode has stronger nonlinearity, but negligibly affects the upper layer. Qualitative and, in some cases, quantitative agreement with observations is obtained. The kinetic energy spectra for the subthermocline can exhibit the k scaling as the upper layer, jointly driven by the KC and LUC instability. Moderate centrifugal instability is identified for the LUC near the topography, leading to locally enhanced submesoscales and eddy fluxes. The present model has the potential to serve as a benchmark for global WBUCs, providing theoretical explanations to observational trends and helping improve the modelling for multi-layer circulations.
How to cite: Chen, X. and Gan, J.: On the nonlinear instability and submesoscale turbulence for western boundary currents and undercurrents , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15575, https://doi.org/10.5194/egusphere-egu26-15575, 2026.
The representation of the Meridional Overturning Circulation (MOC) remains a major source of uncertainty in climate models, since different models show largely different upwelling pathways and magnitudes. The present paradigm is that the MOC consists of a quasi-adiabatic middepth overturning that is mainly Southern Ocean wind-driven with little interior diabatic transformation, and a deep cell that is mixing driven. However, often the mixing and associated diapycnal transports are diagnosed without explicitly accounting for spurious numerical mixing, which may affect water mass transformation in models.
Here, we assess the role of such numerical mixing in shaping diapycnal transport and overturning circulation in models by using the unstructured-mesh ocean model FESOM2 in an idealized Neverworld2 configuration. We do this in two idealized configurations: one with parameterized eddies and one in which eddies are resolved (the latter being finer). By comparing vertical mixing profiles and their horizontal distributions, and by exploiting FESOM2's discrete variance decay and water-mass transformation diagnostics, we identify potential sources of spurious mixing and quantify its contribution to the diapycnal upwelling in the model.
How to cite: Beauregard, G., Griesel, A., Pollmann, F., Eden, C., Scholz, P., and Danilov, S.: How much Overturning is Numerical? Identifying Numerical Mixing in Idealized Ocean Model Experiments. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12320, https://doi.org/10.5194/egusphere-egu26-12320, 2026.
Mixing and Water Mass Transformations (WMT) in the ocean are key to the dynamics, ranging from small-scale dissipation to large-scale overturning circulations. Therefore, the quantification of mixing and WMT in ocean models is of fundamental importance and enables a more detailed analysis of oceanic processes. In this presentation different diagnostic approaches developed during the last years are reviewed and compared. These diagnostic methods also offer to investigate the contributions originating from discretization errors in the numerical transport schemes, causing spurious numerical mixing and spurious overturning circulations. Subtleties of the methods and recent refinements will be presented to provide an accurate analysis framework that is consistent with analytical theories and the discrete model equations.
How to cite: Klingbeil, K.: Analyzing Mixing and Water Mass Transformations in Ocean Models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21305, https://doi.org/10.5194/egusphere-egu26-21305, 2026.
Posters virtual: Tue, 5 May, 14:00–18:00 | vPoster spot 1a
EGU26-221 | ECS | Posters virtual | VPS20
Induced Diffusion of Interacting Internal Gravity WavesTue, 05 May, 14:27–14:30 (CEST) vPoster spot 1a
Induced diffusion (ID), an important mechanism of spectral energy transfer due to interacting internal gravity waves (IGWs), plays a significant role in driving turbulent dissipation in the ocean interior. In this study, we revisit the ID mechanism to elucidate its directionality and role in ocean mixing under varying IGW spectral forms, with particular attention to deviations from the standard Garrett-Munk spectrum. The original interpretation of ID as an action diffusion process, as proposed by McComas et al., suggests that ID is inherently bidirectional, with its direction governed by the vertical-wavenumber spectral slope σ of the IGW action spectrum, n ~ mσ. However, through the direct evaluation of the wave kinetic equation, we reveal a more complete depiction of ID, comprising both a diffusive and a scale-separated transfer rooted in the energy conservation within wave triads. Although the action diffusion may reverse direction depending on the sign of σ (i.e., red or blue spectra), the net transfer consistently leads to a forward energy cascade at the dissipation scale, contributing positively to turbulent dissipation. This supports the viewpoint of ID as a dissipative mechanism in physical oceanography. This study presents a physically grounded overview of ID and offers insights into the specific types of wave-wave interactions responsible for turbulent dissipation.
How to cite: Wu, Y. C. and Pan, Y.: Induced Diffusion of Interacting Internal Gravity Waves, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-221, https://doi.org/10.5194/egusphere-egu26-221, 2026.
