Langmuir circulations arise through the interaction between the Lagrangian drift of the surface waves and the wind-driven shear layer. The high shear rate alone is sufficient for generating quasi-streamwise vortices within the shear layer. Despite the different formation mechanisms, both vortical structures manifest themselves by inducing wind-aligned streaks on the surface. Numerical simulations of a stress-driven turbulent shear layer bounded by monochromatic surface waves are conducted to reveal the mutual interaction between the large-scale vortical structures of Langmuir circulations and the small-scale quasi-streamwise vortices in Langmuir turbulence. The averaged structure of Langmuir circulations is educed from conditional averaging guided by the signatures of predominant surface streaks obtained from empirical mode decomposition. The width of the averaged vortex pair of Langmuir circulations is found to be comparable to the most unstable wavelength of the wave-averaged Craik–Leibovich equation. Small-scale coherent vortical structures are identified using a detection criterion based on local analysis of the velocity-gradient tensor and their topological geometry. Quasi-streamwise vortices accumulated beneath the windward surface are found to dominate the distribution of small-scale coherent vortical structures. Employing the variable-interval spatial average to the identified quasi-streamwise vortices reveals that they tend to form in the edge vicinity of the high-speed surface jets induced by the Langmuir cells. The tilting of vertical vorticity at the outer edges of surface jets by shear current and wave drift enhances the formation of quasi-streamwise vortices. The results highlight the differences in the coherent vortical structures between the Langmuir turbulence and the turbulent wall layer.

How to cite: Tsai, W. and Lu, G.: Interaction between large-scale vortical structures and quasi-streamwise vortices in Langmuir turbulence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10245, https://doi.org/10.5194/egusphere-egu23-10245, 2023.

The knowledge of how seawater moves around in the global ocean and transports tracers and particulates, is crucial for solving many outstanding issues in physical oceanography and climate science. Due to limited available observations, seawater pathways are often estimated by evaluating virtual particle trajectories inferred from velocity fields computed with ocean models. The quality of these Lagrangian analyses strongly depends on how well the underlying ocean model represents the ocean circulation features of interest.
Here, we investigate how simulated surface particle dispersal changes, if the – often omitted or only approximated – impact of surface waves is considered. Specifically, we test the impact of new representations of wave-current interactions for the ocean model NEMO in a case study for the Mediterranean Sea. We are using velocity output from a high-resolution (1/24°) ocean-only model simulation as well as a complementary coupled ocean-wave model simulation, to answer the following questions: How do waves impact the simulated surface particle dispersal, and what is the relative impact of Stokes drift and wave-driven Eulerian currents? How well can the wave impact be approximated by the superposition of Eulerian mean and Stokes drift velocity fields obtained from independently run ocean and wave models?
We find that the wave coupling leads to a decrease in the mean surface current speed in summer dominated by wave-driven Eulerian currents, and an increase in the mean surface current speed in winter dominated by Stokes drift. We further show that Lagrangian simulations with superimposed Eulerian currents and Stokes drift from independent ocean-only and wave models do not necessarily yield more realistic results for surface dispersal patterns than simulations that do not include any wave effect. This implies that – whenever possible – velocity fields from a coupled ocean-wave model should be used for surface particle dispersal simulations.

How to cite: Rühs, S., van Sebille, E., Moulin, A., and Clementi, E.: Impact of the representation of waves on simulated particle dispersal in the surface ocean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10993, https://doi.org/10.5194/egusphere-egu23-10993, 2023.

High frequency radars (HFR) are systems that allow us to monitor some oceanographic variables through the backscatter signal from the ocean surface.  Typically, they provide us with a relatively high space-time resolution of surface currents and the wave field, very important local information to be used for maritime operation applications, such as search and rescue, safety at sea and transportation, and marine energy resources assessment.  Although the main product from HFR is ocean surface currents, they can in addition, provide useful information to derive important characteristics of the wave field, such as significant wave height (Hs) and even the directional spectrum. We, nevertheless, focus our attention in this work in the wave field, and specifically Hs values. A HFR (WERA system) is in operation in Todos Santos Bay, Ensenada, Mexico, since March 2021. Maps of significant wave height are estimated every hour over an area of approximately 250 km2 with spatial resolution of 800 m. These measurements have been compared with wave data derived from three moored instruments (ADCP), the results yielded correlations greater than 0.7 and RMSE values less than 40 cm. In the last two decades this technology has been implemented throughout the world, although there is very limited detail on calibration and validation of the instrument with local ocean wave conditions, especially with respect to the presence of swell. In this study, an empirical calibration is performed using an algorithm provided by the manufacturer in which a correction parameter  is obtained according to the operating frequency of the radar, in particular a WERA system. This study takes into consideration some particular characteristics of the area of interest and the performance of the correction parameter is determined as a function of the wave height and direction of travel relative to the radial direction from the WERA site.

How to cite: Guevara Aguirre, J. C., Durazo, R., García-Nava, H., Esquivel-Trava, B., Gomez, R., and Ocampo-Torres, F. J.: Ocean surface wave measurements from a phase array high-frequency radar system in the coastal area of Northwest of Mexico Pacific waters, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17107, https://doi.org/10.5194/egusphere-egu23-17107, 2023.

Ocean surface wave full directional spectrum is estimated directly from measurements obtained with a spar buoy and from synthetic aperture radar images of the sea surface. These two techniques complement each other to provide us with a rather comprehensive view of the dynamical behaviour of surface waves. We focus our study in sea state conditions under varying winds, when frequently mixed sea and swell systems are encountered. These conditions are characterized by non-equilibrium wind-wave systems. Direct measurements of ocean-atmosphere momentum fluxes obtained from dedicated air-sea interaction spar buoy are also analyzed. The aim is to better understand the ocean-atmosphere momentum transfer behaviour and uppermost ocean currents under rapidly varying wind field. Atmospheric cold front passage through the measuring buoy imposed a unique wind-wave system information, especially under the occurrence of cases when swell propagation opposes locally generated wind-waves. Of particular importance is the analysis of the wave field making use of synthetic aperture radar images of the sea surface. The wave and wind fields to both sides of the atmospheric front are analyzed. From the buoy measurements fetch-limited wind sea growth is also determined, where slanting fetch is to be considered as very relevant. In particular, wind acceleration effect on wave growth is addressed, during specific cases when wind direction prevailed relatively constant. Wind-wave growth rate is somewhat greater than stationary conditions, as it can be observed also in some laboratory experiments at least for the early stages of the growth process. 

How to cite: Ocampo-Torres, F. J., Osuna, P., Rascle, N. G., García-Nava, H., Díaz Méndez, G., Esquivel-Trava, B., Villarreal-Olivarrieta, C. E., and Mora-Escalante, R. E.: On the effect of ocean surface waves on air-sea interactions: results from in-situ and remote measurements in the Gulf of Mexico., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17299, https://doi.org/10.5194/egusphere-egu23-17299, 2023.

Major update of the physics of the third generation models will be presented. The new source terms for wind input, whitecapping dissipation, interaction of waves with adverse winds (negative input) and swell attenuation have been developed and implemented in WAVEWATCH-III, SWAN and WAM models. Physics and parameterisations for the new source functions are based on observations, which allowed us to reveal features and processes previously unknown and not accounted for. For extreme conditions, physics of the wind input and whitecapping dissipation terms exhibit additional features irrelevant or inactive at moderate weather.

In particular, the wave growth term was shown to be a nonlinear function of wave steepness (spectral density). Additionally, the wave breaking was found to enhance the wind input. Relative reduction of the wind input at strong-wind/steep-wave conditions was observed, due to full flow separation found at such circumstances. At strong wind forcing, this causes saturation of the sea drag.

Spectral distribution of the whitecapping dissipation is the most elusive function to measure. Breaking of waves, and hence such dissipation exhibits a clear threshold behaviour in terms of wave steepness (or saturation spectrum). Other novel observed features are cumulative effect away from the spectral peak (dissipation is not local in wavenumber space), directional bimodality. It was found that at moderate winds the dissipation is fully determined by the wave spectrum whereas at strong winds it is a function of the wind speed.

In absence of breaking (swell or other circumstances when the spectral density is below the threshold), other energy sink has to be invoked. It is based on observations of wave-turbulence interactions, and dependence of such interactions on wave steepness.

Interaction of the waves with adverse wind is a necessary additional term if the above-mentioned wind input function is employed, since this function only describes forcing of waves by the following wind. These dependences are calibrated by means of observations in tropical cyclones.

In order to test the source functions independently, and control the flux balance in the model, additional observation-based constraints are implemented. At each time step, the total momentum input is verified to match an independently known wind stress.

Qualitative and quantitative effects and properties of the observation-based source terms are parameterised, and the parameterisations are presented in forms suitable for spectral wave models. The new versions of the models have undergone extensive testing by means of academic tests, regional and global wave hindcast, modelling extreme conditions ranging from tropical cyclones to the marginal ice zone.

How to cite: Babanin, A.: Observation-Based Physics in Spectral Wave-Forecast Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4788, https://doi.org/10.5194/egusphere-egu23-4788, 2023.

The hydrodynamical process of breaking water waves is still a source of many unsolved questions. An extensive research work has been carried out during the last decades in order to quantify and define the associated energy redistribution, which directly influences a wide range of climate processes, maritime applications, and oceanic phenomena.

Naturally, waves become steeper toward the inception of breaking; however, there is still a lack of unanimity regarding the relationship between breaking probability statistics and wave steepness. Here we present a detailed analysis of different sea states from the Black Sea measurements and from a closed wind-wave flume experiments. Together with the wind-derived parameters, the water wave statistics were gathered using an innovative breaking wave detection algorithm. The algorithm was recently developed to allow accurate detection of breaking waves based on the phase-time approach and wavelet analysis to identify breaking-associated patterns in the instantaneous frequency variations of surface elevation fluctuations. The in-depth analysis of breaking and non-breaking wave statistics included wave-by-wave calculations resulting in steepness and celerities of the local wave, derived from the local wave frequency and wavenumber. Finally, the findings, after investigation and validation, presented a skewed Gaussian-like steepness histogram, revealing that both non-breaking and breaking waves can reach steep profiles, above the Stokes limit. 

How to cite: Liberzon, D., Knobler, S., Winiarska, E., and Babanin, A.: Wave Breaking Statistics Under Wind in Sea and Laboratory Conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1090, https://doi.org/10.5194/egusphere-egu23-1090, 2023.

Recent years have seen an extensive increase in maritime activity, including new coastal and offshore infrastructure, increased cargo transport, and research on wave energy converters. While long-term macro-scale wave forecasting has been extensively researched (e.g. Günter & Hasselmann, 1991), with several forecasting models available today, there is a noticeable gap in local-scale deterministic wave forecasting models. Such models are needed to improve the efficiency of the design and operation of offshore installations and vessels, providing close-to-real-time data and short-term predictions of waves and wave-induced forcing.

We will report on the development of a new, computationally efficient model, allowing for weak nonlinearities in directional wavefields, based on previous studies on the unidirectional case (Stuhlmeier & Stiassnie, 2021). The model is capable of providing a deterministic forecast of the wavefield inside the prediction domain in time and space, based on measurements conducted over an initial region (Figure 1).

The mathematical framework used is the Zakharov equation, which determines the nonlinear cross-corrections to the frequencies between the various modes in the spectrum (Stuhlmeier & Stiassnie, 2019), used to derive the actual velocities at which the various wave field components are propagating.

The presentation will elaborate the full mathematical framework, alongside explanations of its benefits with respect to linear predictions. The model’s performance is validated using numerical data of nonlinear directional wavefields, generated using the higher order spectral (HOS) method.

Figure 1 – Predictable region in time (vertical axis) based on measurements at initial domain η₀(x,y)

References

​​Günter, H. & Hasselmann, S., 1991. Wamodel cycle 4, Hamburg: German Climate Computing Centre.

Raphael Stuhlmeier and Michael Stiassnie. Deterministic wave forecasting with the Zakharov equation. J. Fluid Mech., 913:1–22, 2021.

Raphael Stuhlmeier and Michael Stiassnie. Nonlinear dispersion for ocean surface waves. J. Fluid Mech., 859:49–58, 2019.

How to cite: Meisner, E., Liberzon, D., Galvagno, M., Andrade, D., and Stuhlmeier, R.: Deterministic directional wave forecasting in deep water, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9740, https://doi.org/10.5194/egusphere-egu23-9740, 2023.

A localized multiscale energetics framework is used to study the multiscale typhoon-induced upper oceanic responses, in the case of Typhoon Kalmaegi in the South China Sea. A diagnostic methodology of the time-varying energetics, on the basis of the multiscale window transform (MWT) —namely, localized multiscale energy and vorticity analysis (MS-EVA) decomposes HYCOM variable fields into a low-frequency background flow window, a mid-frequency flow window and a high-frequency process window. The background window represents mesoscale processes and Kuroshio currents well and the mid-frequency window captures near-inertial processes influenced by typhoon-induced wind stresses. The scale-scale kinetic energy transfers from the near-inertial window to the background window, mainly on the right-hand side of the typhoon track. Advection and pressure work redistribute energy contribute to the accumulation of kinetic energy in the mid-frequency flow window and enhances ocean mixing. Negative vorticity has a significant impact on the distribution and downward propagation of the near-inertial energy, leading to heterogeneity in the mixing of the upper ocean. We offer new insights into understanding the multiscale interactions between typhoons and the upper ocean.

How to cite: Li, G., He, Y., Yang, Y., Liu, G., Lu, X., and Perrie, W.: Multiscale analysis of typhoon-induced oceanic responses: A Case Study of Typhoon Kalmaegi in the South China Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1173, https://doi.org/10.5194/egusphere-egu23-1173, 2023.

How to cite: Burde, G.: Ordering of small parameters in nonlinear wave problems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2435, https://doi.org/10.5194/egusphere-egu23-2435, 2023.

Nonbreaking surface waves (NBSWs) induce vertical mixing even under the windless condition (WLC).  Recent laboratory experiments (e.g., Dai et al. 2010) demonstrated this mixing clearly; stratified water was vertically mixed by the NBSWs under the WLC.  The estimated vertical diffusivity amounts to O(10^-5 m²/s), two orders of magnitude lager than the molecular diffusivity.  Yet, the mechanism of the mixing was not clarified in this laboratory experiment.   Recent numerical studies (e.g., Tsai et al. 2017; Fujiwara et al. 2020) on the other hand showed that the NBSWs under the WLC formed streamwise vortices  beneath the water surface through the CL2 mechanism like Langmuir circulations.  However, the intensity of the mixing was not evaluated in their numerical studies due to short integration time or artificially large eddy viscosity/diffusivity.  As a consequence, how the NBSWs under the WLC could induce the vertical mixing remains to be investigated.  In fact, local generation of turbulence by the wave orbital velocity is proposed as another mechanism of the NBSW-induced turbulence (e.g., Dai et al. 2010; Qiao et al. 2016).  Here, in order to investigate whether and how the NBSW alone could induce such the large vertical mixing, we performed a direct numerical simulation (DNS) of the NBSW under the WLC as in Dai et al. (2010).  The DNS with a sigma-coordinate free-surface nonhydrostatic model reveals that streamwise vortices like Langmuir circulations, developed exponentially at first, grow to be finite amplitude and keep slowly increasing in size and intensity.  At the finite-amplitude stage, the simulated water temperature was vertically mixed from near the surface.  The vertical eddy diffusivity was O(10^-5 m²/s) very near the surface, which is overall similar to the previous estimation (Dai et al.  2010), but its vertical profile was different.  Enstrophy analysys reveals that CL2 mechanism, the same as for Langmuir circulations, kept working even in the finite-amplitude stage to induce the intense mixing near the surface.

How to cite: Yoshikawa, Y., Imamura, H., and Fujiwara, Y.: A direct numerical simulation of nonbreaking-surface-waves induced mixing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11149, https://doi.org/10.5194/egusphere-egu23-11149, 2023.

FIO-ESM (First Institute of Oceanography-Earth System Model) developed by the First Institute of Oceanography of the Ministry of Natural Resources, is an earth system model with surface gravity wave models and composed of a physical climate model and a global carbon cycle model. The Earth system model has developed from FIO-ESM v1.0, to FIO-ESM v2.0, which has been improved in both its physical climate model and the global carbon cycle model. The marine carbon cycle model of FIO-ESM v2.0 global carbon cycle model has been upgraded from the nutrient-driven model of v1.0 to the NPZD (Nutrient Phytoplankton Zooplankton Detritus) type ocean ecological carbon cycle model, and the terrestrial carbon cycle model has been upgraded from the simple light energy utilization model of v1.0 to the carbon-nitrogen coupling model considering carbon-nitrogen interaction. The atmospheric carbon cycle model is still the CO₂ transport processes, with the anthropogenic carbon emissions from the fossil fuel and land use change. In terms of effects of physical process parameterization schemes on the global carbon cycle, the FIO-ESM v2.0 global carbon cycle considers not only the role of non-breaking wave induced mixing on biogeochemical variables, but also the effects of SST diurnal cycle on air-sea CO₂ flux. Primary analysis shows that FIO-ESM v2.0 can simulate the global carbon cycle fairly well after considering more complex carbon cycle processes.

How to cite: Bao, Y.: Global Carbon Cycle of Earth System Model FIO-ESM with Surface Waves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4824, https://doi.org/10.5194/egusphere-egu23-4824, 2023.

As the time and spatial scales of surface waves are several seconds and hundreds meters, which are much smaller than those of ocean circulation and climate, months and thousands kilometers or even bigger. As a result, ocean surface wave models are separated from ocean circulation models and climate models as different streams. During the past 2 decades, we find that surface waves play dominant role in the vertical mixing of the upper ocean, and heavily modulate the air-sea momentum and heat fluxes. (1) By including surface waves into ocean general circulation models (OGCMs), the ever-standing simulated shallow mixed layer and over-estimated sea surface temperature (SST) especially in summer faced by nearly all OGCMs are dramatically reduced, 80-90% common errors can be removed from OGCMs; (2) Although the forecasting error of Tropical Cyclone (TC) track is reduced by about half during the past 3 decades, the forecasting of TC intensity has no much progress. By including surface waves, the TC intensity error is reduced by about 40%; (3) SST is a crucial parameter in climate system. All climate models have huge SST simulation bias which has last for half century. By including surface wave, the SST bias can be reduced by about half. All above suggests that surface waves should be included in ocean, TC and climate models for improving our forecasting ability on ocean, TC and climate.

How to cite: Qiao, F.: Surface waves can much improve ocean to climate models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6244, https://doi.org/10.5194/egusphere-egu23-6244, 2023.

Model resolution and the included physical processes are two of the most important factors those determine the realism or performance of ocean model simulations. In this study, a new global surface wave-tide-circulation coupled ocean model FIO-COM32 with a resolution of 1/32°×1/32° is developed and validated. Promotion of the horizontal resolution from 1/10° to 1/32° leads to significant improvements in the simulations of surface eddy kinetic energy (EKE), main paths of the Kuroshio and Gulf Stream, and the global tides. We propose the Integrated Circulation Route Error (ICRE) as a quantitative criteria to evaluate the simulated main paths of Kuroshio and Gulf Stream. The non-breaking surface wave-induced mixing (Bv) is proven to still be an important contributor that improves the agreement of the simulated summer mixed layer depth (MLD) against the Argo observations even with a very high horizontal resolution of 1/32°. The mean error of the simulated mid-latitude summer MLD is reduced from -4.8 m in the numerical experiment without Bv to -0.6 m in experiment with Bv. By including the global tide, the global distributions of internal tide can be explicitly simulated in this new model and are comparable to the satellite observations. Based on Jason3 along-track sea surface height (SSH), wave number spectral slopes of mesoscale ranges and wave number-frequency analysis show that the unbalanced motions, mainly internal tides and inertia-gravity waves, induced SSH undulation is a key factor for the substantially improved agreement between model and satellite observations in the low latitudes and low EKE regions. For ocean model community, surface waves, tidal currents and ocean general circulations have been separated artificially into different streams for more than half a century. This paper demonstrates that it should be the time to merge these three streams for new generation ocean model development.

How to cite: Xiao, B., Qiao, F., Shu, Q., Yin, X., Wang, G., and Wang, S.: Development and validation of a global 1/32° surface wave-tide-circulation coupled ocean model: FIO-COM32, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4850, https://doi.org/10.5194/egusphere-egu23-4850, 2023.

The behavior of drag coefficient (C_D) in two different motion-relative quadrants of Typhoon Mujigae (2015) is investigated through the flux observations conducted on a fixed platform over the coastal region in the northern South China Sea. Observations reveal that the variation of C_D is closely related to the location relative to the tropical cyclone (TC) center. The C_D  presents an enhancement when the typhoon is away from the observational site. The spatial distribution of C_D on the periphery of a TC is asymmetric, and the C_D in the right rear quadrant is much larger than that in the right front quadrant for the same wind speed range. This asymmetric distribution of C_D can be explained by the differences in wave properties between the two quadrants. C_D is smaller in cross-swell conditions than that in the along-wind wave conditions. Observations also confirm that C_D tends to level off and even attenuate with the increase of wind speed, and the critical wind speed for C_D saturation over the coastal region (~20 m/s) is much lower than that over the open ocean (~30 m/s). The observational spatial distribution of C_D in TC quadrants not only improves our understanding on the air-sea momentum flux but also provides a potential solution for the long-standing scientific bottleneck on TC intensity forecasting.

How to cite: Chen, S.: Observed Drag Coefficient Asymmetry in a Tropical Cyclone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11366, https://doi.org/10.5194/egusphere-egu23-11366, 2023.