Using an explicit representation or a parametrisation of the ocean mesoscale affects not only the mean state of the ocean but also the climate variability. However, the choice of resolution is constrained by computational costs. Ocean models developed at the Met Office are used for a vast range of applications from short-range coupled NWP forecasts to Earth system models. Shorter range predictions can run with higher resolution models while climate models are very constrained. To support all applications, we developed a hierarchy of three ocean models: eddy parametrising (1°), eddy-present (1/4°) and eddy-rich (1/12°) resolution models. In the eddy parametrising configuration, mesoscale eddies are not resolved. In the eddy-present configuration, the resolutions allow some mesoscale eddies to be captured in the low and mid-latitudes. In the eddy-rich configuration, eddies are present at most latitudes.

In the 1° configuration, the mesoscale turbulence associated with eddies cannot be solved explicitly. The lateral turbulent fluxes are assumed to depend linearly on the lateral gradients of large-scale quantities requiring second order operators. A lateral diffusion of momentum on geopotential surfaces with a Laplacian viscosity is used. The effect on the large scale is represented using Gent and McWilliams (1990) proposed parameterisation of mesoscale eddy-induced turbulence. In the 1/4° and 1/12° configurations, the more scale selective biharmonic operator is used. It ensures the stability of the model while not interfering with the resolved mesoscale activity. To improve the circulation and biases in the Southern Ocean, a weak GM parametrisation is added in the eddy-present and eddy-rich models.

30-year forced integrations with the model hierarchy are assessed. Global and large-scale temperature and salinity biases are similar across the resolutions.  The largest differences occur in regions with strong mesoscale activity (Western boundary currents, Southern Ocean). Eddy-present and eddy-rich models significantly improve the representation of the Western boundary currents, both in position and strength. Improving the Western boundary currents has large impacts on temperature and salinity biases.

We review the results of Moreton et al (2020) on eddies in the Met Office hierarchy of models. The surface properties of eddies in eddy-present and eddy-rich coupled models are evaluated using an eddy tracking algorithm on SSH anomalies. Results show that relative to eddy-present, eddy-rich resolution simulates more (+60%) and longer-lasting (+23%) eddies, in better agreement with observations. The representation of eddies in Western Boundary Currents and the Southern Ocean compares well with observations at both resolutions.  However, a common deficiency in the models is the low eddy population in subtropical gyres. Despite a grid spacing larger than the Rossby radius of deformation at high-latitudes, eddy-present resolution only allows for eddy growth in these regions a lower rate than seen in observations and eddy-rich resolution. The westward displacement of eddies in eddy-rich model (mainly in the Agulhas region) is increased compared to the eddy-present model. The size of eddies is found to be dependent on model grid resolution.

How to cite: Guiavarc'h, C., Hewitt, H. T., Moreton, S. M., Roberts, M., and Storkey, D.: Representation of mesoscale in a hierarchy of Met Office ocean model configurations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17233, https://doi.org/10.5194/egusphere-egu23-17233, 2023.

Our understanding of the ocean’s spatial scales and their coupling has been derived mostly from Fourier analysis in small "representative" regions, typically a few hundred kilometers in size, that cannot capture the vast dynamic range at planetary scales. Using coarse-graining, we analyze a 1/12-degree reanalysis dataset on a range of spatial scales spanning more than three orders of magnitude, including both mesoscales and planetary scales. We present a truly global kinetic energy wavenumber spectrum, as well as the first measurements of the cascade across this entire range of scales. This provides us with the first estimates of the global amount of energy that is transferred by the KE cascade, as well as the scale-dependent depth structure of the oceanic KE spectrum and cascade. We find that within the mesoscales, the seasonal cycles of KE at larger length scales demonstrate a characteristic lag time relative to smaller length scales. The seasonal cycle of the inverse energy cascade exhibits the same lag time but is phase-shifted to earlier times, which suggests causality.

How to cite: Storer, B., Buzzicotti, M., Khatri, H., Griffies, S., and Aluie, H.: Energy Spectra and Cascades in the Global Ocean: Planetary Scales to Mesoscales, Surface to the Abyssal Ocean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-561, https://doi.org/10.5194/egusphere-egu23-561, 2023.

The transfer of kinetic energy between currents of different horizontal scales shapes the structure of the global ocean circulation and associated heat, salt, nutrient, and oxygen fluxes, as well as atmosphere-ocean interactions. In particular the geostrophically balanced part of the flow has been shown to be associated with a net inverse cascade from currents of smaller scales to currents of larger scales. Here, we show with a submesoscale-permitting simulation of the Atlantic that the respective scale kinetic energy flux averaged over 5º x 5º boxes is linearly related to the product of quantities that are computable from along-track altimetry when they are averaged over the same region. This linear relationship is applied to JASON-3 along-track sea-surface height data to estimate for the first time the geostrophic kinetic energy cascade at scales between 60 and 200 km, as well as its regional distribution and seasonal cycle for large parts of the global ocean on the basis of observations. The results are consistent with previous findings based on regional observations, simulations, and indirect comparisons of spectral properties of satellite data.

How to cite: Schubert, R. and Gula, J.: Estimating the Oceanic Kinetic Energy Cascade from Satellite Along-Track Altimetry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2773, https://doi.org/10.5194/egusphere-egu23-2773, 2023.

Mesoscale eddies play a key role in the transport and mixing of ocean tracers such as heat and carbon. They widely contribute to the stratification of the ocean and form the highest reservoir of kinetic energy. However, although baroclinic instabilities are believed to be a central mechanism of eddy generation, little is known about their dissipation. Notably, how and where the kinetic energy flows out from the mesoscale reservoir remains uncertain. In the ocean, the mechanical energy is dissipated by a variety of processes but only a small part occurs in the top few hundred meters of the water column, adding some difficulty to their measurement. 

Here, a simplified equation of the mesoscale energy budget is used to get a global estimation of the eddy dissipation rate. We first validate this framework in a global ocean simulation using a parameterized eddy energy budget. With the ocean stratification as the main input, we then apply this framework to an observation-based density climatology and a global reconstruction of the eddy kinetic energy field. We find a global mesoscale dissipation rate of about 0.45 TW, in agreement with recent independent estimates. The results also show an intense dissipation near western boundary currents, where both large levels of energy and large baroclinic conversion rates occur.  The resulting dissipation map brings new insights for closing the ocean kinetic energy budget as well as constraining future mesoscale parameterizations and associated mixing processes.

How to cite: Torres, R., Waldman, R., Mak, J., and Séférian, R.: Global estimate of eddy dissipation from a diagnostic energy balance, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1533, https://doi.org/10.5194/egusphere-egu23-1533, 2023.

Quantifying and understanding the mixing and decay properties of oceanic mesoscale coherent eddies is crucial, as coupled climate models become eddy-permitting. Measuring experimentally the decay of coherent eddies is a difficult and expensive task. As of now, only a very limited number of repeated field surveys across the same eddy have been achieved. On the other hand, satellite altimetry offers a nearly synoptic two-dimensional view of the evolution of ocean vortices, and the record is now 30 years-long, allowing for the computation of solid statistics. But most coherent eddies are essentially baroclinic and knowledge of their vertical structure is crucial to understand the decay of their energy, or heat and salt contents. Here, we take advantage of the dense array of ARGO float profiles in the Gulf of Mexico (GoM) to reconstruct the three-dimensional structure of all Loop Current Rings (LCR) detached since 1993, using the Gravest Empirical Modes (GEM) method and a gridded altimetry product. The 3D reconstruction method was validated using independent glider observations and exhibits a striking accuracy in estimating the kinetic and available potential energy of LCRs, as well as their heat and salt contents. The decay of LCRs in terms of energy and thermohaline properties is then studied in details and it is shown that, despite their longevity of 6 to 15 months, they decay continuously with time at an inverse exponential rate, and have lost 80 % of their total energy as they reach the western GoM’s continental slope, where they were previously suspected to decay. We studied the impact of the wind and the feed back of the current on the wind on the energy decay of LCRs, and found that wind stress work (using relative wind stress), is responsible for half of the total energy loss during the eddy’s life time, while available potential energy decay is entirely driven by Ekman buoyancy fluxes and the barotropic vorticity decay is driven by wind stress curl. This suggests that wind forcing (when considering the feed-back of ocean currents on wind stress) is the leading-order mechanism in the decay of these coherent eddies.

How to cite: Meunier, T., Bower, A., and Perez Brunius, P.: Estimating and Understanding the Energy Decay of Coherent Eddies from In situ Observations and Satellite Altimetry., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2884, https://doi.org/10.5194/egusphere-egu23-2884, 2023.

The Gulf Stream (GS) is one of the strongest ocean currents on the planet. Eddy-rich resolution models are needed to properly represent the dynamics of the GS, however kinetic energy (KE) can be in excess in these models if not dissipated efficiently. The question of how and how much energy is dissipated and in particular how it flows through ocean scales thus remains an important and largely unanswered question. Using a high-resolution (2 km) ocean model (CROCO), we characterize the spatial and temporal distribution of turbulent cascades in the GS based on a coarse-grained method. We show that the balanced flow is associated with an inverse cascade while the forward cascade is explained by interactions between unbalanced and balanced motions. The forward cascade, which represents an interior route to dissipation, is compared to both numerical and boundary dissipation processes. The contribution of interior dissipation is an order of magnitude smaller than that of the other energy sinks.

How to cite: Contreras, M., Renault, L., and Marchesiello, P.: Understanding Energy Pathways in the Gulf Stream, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2789, https://doi.org/10.5194/egusphere-egu23-2789, 2023.

Direct measurements of dissipation rates in the Southern Ocean unveiled a deficit of lee-wave dissipation compared to lee-wave generation (Brearley et al. 2013; Sheen et al. 2013; Waterman et al. 2013, 2014; Cusack et al. 2017, 2020), which is described as “suppression of turbulence” in Waterman et al. (2014). One possible explanation is the generation of freely propagating internal gravity waves (free waves with Eulerian frequency 𝜔_𝐸 ≠ 0) that can radiate outside of the lee-wave critical layer and dissipate remotely. In a numerical simulation of lee waves generated by a localized, stable geostrophic current over sinusoidal topography, free waves are observed to emanate from the lee-wave critical layer. The escaped fraction of free-wave energy (the fraction that tunnels through the lee-wave critical layer and reaches the upper ocean) is 5%, while the majority remains trapped. This excludes remote dissipation by free waves as an explanation for the observed “suppression of turbulence”. Energy budget calculations show that ~50% of the bottom-generated lee-wave radiation is reabsorbed into the geostrophic current in vertical mean shear, ~10% is transferred to free waves as an indirect route to dissipation, and ~40% is lost through nonlinear wave-wave interactions leading to the increase of background potential energy. The total dissipative fraction (dissipation of lee waves plus indirect dissipation as free waves) is consistent with predictions by wave action conservation, regardless of the selected eddy viscosity and diffusivity. This study emphasizes wave-mean and wave-wave interactions in the ocean and will shed light on the choice of turbulent parameterization schemes for numerical modelers.

How to cite: Wu, Y., Kunze, E., Tandon, A., and Mahadevan, A.: Gravity-Wave Emission from Lee-Wave Critical Layers and Energy Budgets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-308, https://doi.org/10.5194/egusphere-egu23-308, 2023.

The continuing retreat of sea ice affects the Arctic mesoscale eddies, and its future evolution will strongly influence air-sea-ice interactions. However, knowledge of eddy activity is limited to sparse observations and coarse resolution models. How future eddies and their effects will evolve remains uncertain. Here, we apply the global unstructured model FESOM2 for 143 years of 4.5 km-Arctic simulations up to 2100 and 1 km-Arctic simulations for 5 years from 2010; 2090 to reveal the interactions between eddies, winds, sea ice and the energy budget of eddy kinetic energy (EKE) in a high resolution view. We demonstrate a significant increase in future Arctic EKE from 0-200 m, which is stronger in summer when sea ice melts. The future abundance of EKE can be explained by an increase in winter eddy generation and a decrease in summer eddy dissipation. This also leads to an enhancement of the horizontal velocity field, thus filling the Arctic Ocean with eddies in the future.

How to cite: Li, X., Wang, Q., Koldunov, N., Danilov, S., Jung, T., and Müller, V.: Eddy-rich Arctic as future Sea ice disappears in high-resolution view, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5050, https://doi.org/10.5194/egusphere-egu23-5050, 2023.

Ocean internal tides are both ubiquitous and important for the transport of tracers and the meridional overturning circulation, because of the mixing in the deep ocean they cause when they break. They are specific kind of internal waves generated when the astronomical tide encounters topographic features, which can propagate over more than a thousand kilometres. This long range propagation leaves opportunities for these waves to interact with mesoscale flows and eddies, which can be of comparable length scale. These interactions are of importance since they impact both the wavelength and the phase of internal tides, making them difficult to map using satellite altimeter once they have lost their coherency with the astronomical forcing. These interactions may also impact the energy budget of the internal tide and the cascade of energy from the astronomical (barotropic) tide to shorter internal waves (down to scales under 1 km), down to 3D turbulence and dissipative scale. 

In this presentation, we will describe the energy life cycle of internal tides in the North Atlantic basin using outputs from the numerical simulation eNATL60. This simulation has an horizontal resolution of around 2 kilometres and 300 vertical levels. Using a vertical mode decomposition, we investigate the energy budget of the semi-diurnal internal tide and more precisely the exchanges of energy between modes triggered by the topography, the mesoscale flow and the variations of the ambient density field, as well as their time variability.

We will focus on two contrasted areas of the North Atlantic: the Azores Islands and the North mid Atlantic ridge with a weak mesoscale activity and strong topographic features, such as seamounts and a ridge, and the Gulf Stream area featuring a strong western boundary current as well as a continental shelf break.
In the vicinity of the Azores, topographic induced couplings are of leading order for mode 0 and 1 and induce a substantial transfer of energy from low to high modes. The fraction of energy transferred toward high modes by the topography is almost 100% of the total transfer, but advection by the balanced flow becomes significant in the energy budget for modes 2 or higher.
In contrast, in the Gulf stream region, interactions with the mesoscale balanced flow accounts for more than 35% of the energy transfer from low baroclinic modes to high modes, and the mesoscale plays an important role in the energy budget for all baroclinic modes. The most prominent contribution it is the advection by the mean flow: it accounts for 26% of this transfer toward high modes and dominate over topographic scattering for modes 1 to 10.

Advection of the internal tides is the dominant contribution of the interaction between internal tides and the mesoscale balanced flow in the two areas. We find that the internal tide only weakly extracts energy from the mesoscale flow and associated buoyancy field in the two areas.

How to cite: Bella, A., Lahaye, N., and Tissot, G.: Importance of the mesoscale circulation in the energetic of internal tides in two contrasted areas of the North Atlantic., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8066, https://doi.org/10.5194/egusphere-egu23-8066, 2023.

The Weddell Sea is an Antarctic marginal sea featuring extensive continental shelf areas. Here, dense water is produced through interactions with ice shelves and sea ice and propagates down the continental slope where it forms the densest contribution to the Antarctic Bottom Water. The downflow of dense water creates an isopycnal connection between the continental shelf and slope allowing for the intrusion of warm Circumpolar Deep Water (CDW) onto the continental shelf. When reaching the ice shelf cavities, CDW has the potential to strongly increase the melt rate of the ice shelves with global implications such as sea level rise. Mesoscale eddies sourced from local baroclinic instability play a central role in the shoreward transport of CDW since they supply the momentum to overcome the vorticity gradient imposed by the continental slope. Capturing these eddies in ocean models is particularly challenging because the small Rossby radius of deformation at high latitudes requires a much higher horizontal resolution than currently available in state-of-the-art climate models. This invites the question as to how the shoreward heat flux can be parameterised at coarse resolution and motivates a process oriented modelling study. For this purpose we use the MIT general circulation model (MITgcm) in a configuration featuring idealised sloping topography and surface forcing and typical hydrographic fields representing the Weddell Sea continental shelf and slope. In this setup, a strong heat transport from the open ocean onto the continental shelf only emerges at a resolution of O(1km). At coarser resolution, shoreward heat transport is almost absent resulting in a cold bias on the continental shelf and the exported deep water. We then apply the classical schemes of Gent-McWilliams and Redi (GM/Redi) which parameterise the effect of eddies by introducing an advective tracer flux as a function of the isopycnal slopes and by aligning the diffusion operator with the local isopycnals. We show that using the GM/Redi parameterization shoreward heat transports can be represented so that the difference between the high and coarse resolution hydrographic fields strongly reduces. Advective heat transport dominates over the centre of the continental slope and is captured by the GM part of the parameterisation. The diffusive heat flux dominating over the continental shelf break on the other hand is reproduced by the Redi scheme. In light of potential future changes to the Weddell Sea system we further discuss different approaches to obtain the transfer coefficients needed for the GM/Redi parameterisation based on the resolved flow and sub-grid eddy kinetic energy.

How to cite: Dettling, N. and Losch, M.: Parameterising Eddy-Mediated Heat Transports Across the Weddell Sea Continental Slope, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13166, https://doi.org/10.5194/egusphere-egu23-13166, 2023.

How to cite: Draeger-Dietel, J., Griesel, A., Walter, M., Horstmann, J., Carrasco Alvarez, R., and Carpenter, J.: Evidence of a  dual kinetic energy cascade by surface drifter observation in the Walvis Ridge Region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8458, https://doi.org/10.5194/egusphere-egu23-8458, 2023.

We investigate the interaction of internal gravity waves (IGW) with mesoscale eddies using the novel numerical Internal Wave Energy Model (IWEM). With IWEM, we integrate the radiative transfer equation to investigate the propagation and refraction of IGWs, and the energy exchange between IGWs and mean (eddying) flow. We evaluate the evolution of a typical IGW spectrum with energy density in physical and wavenumber space along a single column and over an eddy cross-section. We compare the simulations with the observations of a coherent mesoscale eddy in the Canary Current System. Results show that the changes in IGW energy are dominated by wave propagation effects, wave-mean flow interaction and wave breaking at critical layers, while wave capture effects are two orders of magnitude smaller. The wave propagation terms transport IGW energy from the eddy center to the rim. Energy gain by wave-mean flow interaction is dominated by low-frequency waves in the eddy center, while high-frequency waves are trapped in a cyclo-stationary up-/downward propagation cancelling out their gain or loss of energy. Energy loss by wave-mean flow interaction or wave breaking is largest at the eddy rim, where IGWs undergo a downscale energy transfer to small vertical scales and to the inertial frequency. Mooring observations agree with our model results on higher IGW energy values at the eddy center compared to the rim.  Following the Osborn-Cox relation, wave-breaking induced vertical diffusivities are found to be maximal at the eddy rim and range between κ≅10^-7-10^-5m²s^-1, partly in range with the observed values in the ocean. The interaction of IGWs and mesoscale eddies is therefore a plausible process for explaining the near-surface enhanced mixing. 

How to cite: Sebastia Saez, P., Eden, C., and Chouksey, M.: Interaction of Internal Gravity Waves with Meso-Scale Eddies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10083, https://doi.org/10.5194/egusphere-egu23-10083, 2023.

A long-standing challenge in dynamical oceanography is to distinguish nonlinearly intermingled dynamical regimes of oceanic flows. Conventional approaches focus on time-scale or space-scale decomposition. Here, we pursue a dynamics-based decomposition, where a mean flow is introduced to extend the classic theory of wavy and vortical modes. Mainly based on relative magnitudes of the relative vorticity and the modified horizontal divergence in spectral space, the full flow is decomposed into wavy and vortical motions. The proposed approach proves simple and efficient, and can be used particularly for online disentangling vortical and wavy motions of the simulated flows by ever-popular tide-resolving high-resolution numerical models. This dynamical approach, combined with conventional time-scale- or space-scale-based approaches, paves the way for online mixing parameterizations using model simulated vortical (for isopycnal mixing) and wavy (for diapycnal mixing) motions, and for understanding of multi-regime and multi-scale interactions of oceanic flows.

How to cite: Liu, Z., Wang, C., and Lin, H.: A Simple Approach for Disentangling Vortical and Wavy Motions of Oceanic Flows, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1042, https://doi.org/10.5194/egusphere-egu23-1042, 2023.

By analogy with the case of a simple fluid, lateral stirring in the oceans has been traditionally envisioned as the notional form of stirring that minimally perturb the ocean stratification and its potential energy, as originally proposed over 80 years ago. If considered from the viewpoint of adiabatic and isohaline permutations of two fluid parcels, such a view leads to the idea that lateral stirring preferentially takes place on the ‘locally-referenced potential density surfaces’. To remedy the mathematically and physically ambiguous character of the latter, oceanographers then developed the concepts of potential density surfaces, patched potential density surfaces, and approximately neutral surfaces, which have been the cornerstone of isopycnal analysis for many decades. It has also provided the justification for constructing rotated diffusion tensors in terms of the directions parallel and perpendicular to the neutral directions. Nevertheless, while the concepts of neutral directions and neutral surfaces have been around for decades, their validity has never been really challenged nor confirmed experimentally. Worse, there has been little clue so far about how one might go about testing or refuting these concepts.

Part of the problem is that the current theory of quasi-neutral density variables is not currently formulated as a classical falsifiable (in Popper’s sense) physical theory capable of making testable predictions but more as unfalsifiable dogma. To improve on this situation, this work shows how to embed the theory of lateral stirring and lateral stirring surfaces into the APE-based study of the compressible Navier-Stokes equations for realistic seawater (APE standing as Available Potential Energy, as per Lorenz concept). Doing so succeeds in identifying the kind of models that can be studied to shed light on the issue while also making new predictions about lateral stirring that significantly depart from the prevailing view. A key new result is that isoneutral stirring must involve compensating work between buoyancy and thermobaric forces, which cast doubt on its physical realisability. Another key result is that the ‘true’ neutral directions are not those associated with the standard neutral vector, but rather with an APE-based form of the P vector previously identified by Nycander. Although the P-neutrality thus defined appears to coincide with the standard N-neutrality in most of the oceans, the two are found to significantly differ in the polar region and Gulf Stream area, where neutral rotated diffusion tensors are likely to be potentially a significant source of spurious diapycnal mixing. Evidence that this is the case and how to go about remedying the problem will be discussed.

How to cite: Tailleux, R. and Wolf, G.: A new paradigm for lateral stirring and lateral stirring surfaces in the oceans, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12504, https://doi.org/10.5194/egusphere-egu23-12504, 2023.

Asymptotic analysis of surface waves interacting with a wind and a current

Following Miles (1957), surface waves are regarded as perturbations of the wind, modeled as an inviscid parallel shear flow; a water current can be included in the model. The linear stability analysis of the shear flow leads to an eigenvalue problem. The real part of the eigenvalue is the phase speed of the waves while the imaginary part times the wavenumber is the growth rate of the wave amplitude. The streamfunction of the perturbed flow, or eigenfunction, obeys the Rayleigh equation with coupled boundary conditions at the air-water interface. First, I will show how Miles simplified this problem using the small air-water density ratio. Next, for waves whose wavelength is much larger than the characteristic length scale of the shear, I will solve the Rayleigh equation asymptotically and infer the complex eigenvalue. Finally I will show that, in the strong wind limit, the fastest growing waves are those for which the aerodynamic pressure is in phase with the wave slope. 

References:

J. W. Miles, J. Fluid Mech., 3:185–204, 1957.

A. F. Bonfils, D. Mitra, W. Moon, and J. S. Wettlaufer, J. Fluid Mech., 944:A8, 2022.

A. F. Bonfils, D. Mitra, W. Moon, and J. S. Wettlaufer, arXiv:2211.02942.

How to cite: Bonfils, A., Mitra, D., Moon, W., and Wettlaufer, J.: Asymptotic analysis of surface waves interacting with a wind and a current, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16324, https://doi.org/10.5194/egusphere-egu23-16324, 2023.

Small-scale processes govern the transfer of energy and momentum at the coupled atmospheric and oceanic wave boundary layers. The physical wind energy input mechanisms by wave growth remain poorly understood (critical layer theory vs sheltering mechanism).

We conducted laboratory velocity measurements within the first millimeters to centimeters above and below surface waves. A high resolution 2D Particle Image Velocimetry (PIV) system was installed in a wind-wave tunnel at a fetch of approximately 10 m. In addition, wave field properties were captured by Laser-Induced Fluorescence (LIF). Experiments were run with wind waves and wind over mechanical swell. During the measurements, 10-m wind speeds of 5 to 10 m/s were observed, with peak wave ages (c_p/u_*) ranging from 1 to 7.

We will focus on the air phase and describe the modulations of the airflow structure. Furthermore, we will discuss the influence of peak wind-wave conditions (e.g., wave age, slope) on the dynamical role of the critical layer.

How to cite: Tenhaus, J., Buckley, M., Matt, S., and Savelyev, I.: Wind-Wave Energy Flux Measurements using Particle Image Velocimetry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15675, https://doi.org/10.5194/egusphere-egu23-15675, 2023.

The paper is devoted to two-phase flow simulations and investigates the ability of a diffusive interface Cahn-Hilliard Volume-of-Fluid model to capture the dynamics of the air-sea interface at geophysically relevant Reynolds numbers. It employs a hybrid filtered/averaging Improved Detached Eddy Simulation method to model turbulence, and utilizes a continuum model to account for surface tension if the diffuse interface is under-resolved by the grid. A numerical wind-wave tank is introduced to limit computational costs and results obtained for two wind-wave conditions are analyzed in comparison to experimental data at matched Reynolds numbers. The focus of the comparison is on both time-averaged and wave-coherent quantities, and includes pressure, velocity as well as modeled and resolved Reynolds stresses. In general, numerical predictions agree well with the experimental measurements and reproduce many wave-dependent flow features. Reynolds stresses near the water surface are found to be especially important in modulating the critical layer height. It is concluded that the diffusive interface approach proves to be a promising method for future studies of air-sea interface dynamics in geophysically relevant flows.

How to cite: Loft, M., Rung, T., Kühl, N., Buckley, M., Carpenter, J., Veron, F., and Hinze, M.: Two-Phase Flow Simulations of Surface Waves in Wind-Forced Conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15850, https://doi.org/10.5194/egusphere-egu23-15850, 2023.