OS4.3 | Surface Waves and Wave-Coupled Effects in Lower Atmosphere and Upper Ocean
Surface Waves and Wave-Coupled Effects in Lower Atmosphere and Upper Ocean
Co-organized by NP7
Convener: Alexander Babanin | Co-conveners: Fangli Qiao, Miguel Onorato, Francisco J. Ocampo-Torres
Orals
| Wed, 26 Apr, 14:00–15:45 (CEST)
 
Room L3
Posters on site
| Attendance Wed, 26 Apr, 16:15–18:00 (CEST)
 
Hall X5
Posters virtual
| Attendance Wed, 26 Apr, 16:15–18:00 (CEST)
 
vHall CR/OS
Orals |
Wed, 14:00
Wed, 16:15
Wed, 16:15
We invite presentations on ocean surface waves, and wind-generated waves in particular, their dynamics, modelling and applications. This is a large topic of the physical oceanography in its own right, but it is also becoming clear that many large-scale geophysical processes are essentially coupled with the surface waves, and those include climate, weather, tropical cyclones, Marginal Ice Zone and other phenomena in the atmosphere and many issues of the upper-ocean mixing below the interface. This is a rapidly developing area of research and geophysical applications, and contributions on wave-coupled effects in the lower atmosphere and upper ocean are strongly encouraged

Orals: Wed, 26 Apr | Room L3

14:00–14:05
14:05–14:15
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EGU23-1058
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ECS
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On-site presentation
Sagi Knobler, Gil Rilov, and Dan Liberzon

The sea surface temperature increase due to global warming is causing rapid iceberg melting and increased condensation of clouds, each project to a global consequence in the form of sea surface temperature drop during storms, marine heatwaves, sea level rise, and increase in intensification and rate of recurrence of storm weather events.

Here we present the analysis of 30-year-long measurements of sea surface temperature and instantaneous water surface elevation, measured by two buoys moored in separate locations in the climate hotspot area in the Eastern Mediterranean Sea at the depth of 24 meters, two kilometers off the Israeli coastline. Additional long-term measurements of sea level rise from several stations along the Israeli coastline are also integrated into the analysis. The increase in storm weather events was examined in terms of storms’ significant wave height statistics, using peak-over-threshold analysis over the historic data. 

The results showed occurrences of sea surface temperature drop events following storms and of marine heatwaves, positive trends were observed in sea level and in sea surface temperature rise. The last two decades are shown to be characterized by storm intensification. The sea surface rise was correlated against the measured sea surface temperature trends as obtained by the buoys and compared to Copernicus satellite data with remarkable conclusions.

How to cite: Knobler, S., Rilov, G., and Liberzon, D.: Climate Change Trends in The Eastern Mediterranean Hotspot, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1058, https://doi.org/10.5194/egusphere-egu23-1058, 2023.

14:15–14:25
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EGU23-3573
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Highlight
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On-site presentation
Johannes Gemmrich, Leah Cicon, Benoit Pouliot, and Natacha Bernier

Rogue waves are individual ocean surface waves with a height greater than 2.2 times the significant wave height.  They can pose a danger to marine operations, onshore and offshore structures, and beachgoers, especially when encountered in high sea states. The prediction of bulk sea state parameters like significant wave height, period, direction, and swell components is satisfactorily addressed in current operational wave models. Individual wave heights cannot be predicted by those spectral models, and the prediction of rogue wave occurrence has to be in a probabilistic sense.

Previous attempts on such a prediction are based on the Benjamin Feir Index (BFI), which reflects the nonlinear process of modulation instability as the dominant generation mechanism for rogue waves. However, there is increasing evidence that BFI has limited predictive power in the real ocean. Recent studies established the average crest-trough correlation as the strongest single variable to correlate with rogue wave probability.

We demonstrate that crest-trough correlation can be forecast by an operational WAVEWATCHIII wave model with moderate accuracy. Using multi-year wave buoy observations from the northeast Pacific we establish the functional relation between crest-trough correlation and rogue wave occurrence rate, thus calibrating predicted crest-trough correlations into probabilistic rogue wave predictions. Combined with the predicted significant wave heights we can identify regions of enhanced rogue wave risk. Results from a case study of a large storm off Canada’s west coast are presented to evaluate the regional wave model at high seas, and to present the rogue wave probability forecast based on crest-trough correlation.

How to cite: Gemmrich, J., Cicon, L., Pouliot, B., and Bernier, N.: A probabilistic prediction of rogue waves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3573, https://doi.org/10.5194/egusphere-egu23-3573, 2023.

14:25–14:35
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EGU23-6067
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ECS
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On-site presentation
Daniel Santiago Peláez Zapata, Vikram Pakrashi, and Frederic Dias

The directional distribution of ocean waves is of great importance for a better understanding of air-sea interactions. Countless applications in science and engineering, such as, offshore energy production, microseisms prediction, wave climate modelling, coastal erosion, among many others, require precise information about the wave directionality. However, in spite of its importance, this quantity is poorly understood and difficult to accurately model. This study presents observations of the directional spreading parameters obtained from a set of low-cost GPS-based buoys during highly energetic conditions. One of the buoys was anchored off the west coast of Ireland during the HIGHWAVE project. These observations are compared with the measurements of 20 freely drifting buoys deployed in the Bay of Biscay during the SUMOS campaign. Spreading parameters were compared in the framework of widely used parameterisation for the directional distribution. The directional spreading is narrower at the spectral peak and broadens as the frequency moves away towards higher and lower scales. There is a particularly sharp increase in the spreading for f < fp. The results showed that buoy-based observations significantly differ from spatial-based measurements for frequencies around half the spectral peak. The measruements obtained by the drifting buoys show that for 2 < f/fp < 6, the spreading appears to be approximately constant with the frequency and tends to increase again for f > 6fp. The results showed that the directional spreading seems to be independent of the wave age, roughly across the entire range of frequencies.  This may imply that the shape of the directional spectrum is primarily controlled by the non-linear wave-wave interactions rather by the wind forcing.  In the vicinity of the spectral peak, a weakly linear relationship between the directional spreading and the significant wave height was observed.  The results show that as the significant wave height increases by one meter, the spreading decreases by about 4.5°. The preliminary results presented here contribute to the understanding of the directional distribution of ocean waves. However, further observations and comparisons are needed to fully capture the complexity of this phenomenon. Despite being preliminary, these results provide valuable insights and add to the ongoing discussion on this topic. This work was funded by the European Research Council (ERC) under the EU Horizon 2020 research and innovation programme (grant agreement no. 833125-HIGHWAVE). We are very grateful to the scientific team behind the SUMOS campaign for providing the drifting buoys data.

How to cite: Peláez Zapata, D. S., Pakrashi, V., and Dias, F.: Observations of the ocean waves directional spreading during the HIGHWAVE project and SUMOS campaign., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6067, https://doi.org/10.5194/egusphere-egu23-6067, 2023.

14:35–14:45
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EGU23-10740
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Highlight
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On-site presentation
Alfred Osborne

           

The development of quantum computers over the next decade or so suggests that the geophysical sciences may benefit from very rapid computations from “quantum supremacy.” I have developed a pilot project which would help orient researchers to the use of quantum computers. The first step, and the main topic of my talk, would be to quantize a nonlinear wave equation in order that quantum algorithms might be developed. I focus on the nonlinear Schroedinger equation (NLS). The main emphasis is to show that the NLS equation for spatially periodic boundary conditions is a Hamiltonian system: Thus, I derive the solution and the coordinates and momenta in terms of quasiperiodic Fourier series. Then I apply the method of Heisenberg to develop the matrix mechanics of the NLS equation. Quantization arises as the lack of commutation for the product of the coordinate and the momenta matrices of the equation. I also discuss other equations due to the Dysthe, Trulsen and Dysthe, Yan Li and the Zakharov equations. I discuss how the method of matrix mechanics as applied to nonlinear wave equations might be programmed on a quantum computer.

How to cite: Osborne, A.: Computation of Nonlinear Wave Motion Using a Quantum Algorithm, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10740, https://doi.org/10.5194/egusphere-egu23-10740, 2023.

14:45–14:55
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EGU23-16788
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ECS
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On-site presentation
Laura Grzonka and Witold Cieślikiewicz

As waves pass, fluid elements experience not only periodic motion but also a movement in a direction of wave propagation (Stokes, G.G. (1847) On the Theory of Oscillatory Waves. Transactions of the Cambridge Philosophical Society, 8, 441-455). Defined as a difference between the average Lagrangian flow velocity of a particle and the average Eulerian flow velocity of the fluid, the Stokes drift entails, amongst others, the existence of wave-induced mass transport (van den Bremer TS, Breivik Ø. 2017 Stokes drift. Phil. Trans. R. Soc. A 376:20170104. http://dx.doi.org/10.1098/rsta.2017.0104). Knowledge of it is of high significance since it allows one to calculate tracer transport, for instance, plastic or oil pollution.
While operating in the Eulerian frame of reference, one should recognize that a fixed point in space in the vicinity of a free surface emerges and submerges under the water during wave motion. This phenomenon is called the emergence effect and it does impact the particle kinematics properties. Cieślikiewicz & Gudmestad developed a method of calculating the wave-induced mass transport for deterministic and random waves taking into account the emergence effect (Cieślikiewicz, W. & Gudmestad, O. T. (1994). Mass transport within the free surface zone of water waves. Wave Motion, 19(2), 145–158. https://doi.org/10.1016/0165-2125(94)90063-9).
The goal of the study was to introduce numerical examples and verification of both deterministic and random wave cases presented by Cieślikiewicz & Gudmestad (1994) depending on wind wave parameters. Wolfram Mathematica software was used to carry out the calculations and draw figures. The wave energy spectrum was determined using the JONSWAP formula (Hasselmann, K., Barnett, T. P., Bouws, E., Carlson, H., Hasselmann, D. E., Kruseman, P., Meerburg, A., Mûller, P., Olbers, D. J., Richter, K., Sell, W., & Walden, H. (1973). Measurements of wind-wave growth and swell decay during the Joint North Sea Wave Project (JONSWAP). Ergaenzungsheft Zur Deutschen Hydrographischen Zeitschrift, Reihe A., 12(A8), 1–95). The results show that the mass transport values for a representative deterministic wave agree with values for random waves. Therefore, the deterministic wave formulas may be used to initial estimate mass transport induced by random water wave field.

How to cite: Grzonka, L. and Cieślikiewicz, W.: Mass transport induced by nonlinear surface gravity waves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16788, https://doi.org/10.5194/egusphere-egu23-16788, 2023.

14:55–15:05
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EGU23-14060
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Highlight
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On-site presentation
Denis Bourras, Christopher Luneau, Rémi Chemin, William Bruch, Saïd Benjeddou, and Philippe Fraunié

The study of the relationship between wind speed, altitude, and the geometric properties of the ocean surface (characteristics of dominant waves, surface roughness, see the wave-breaking rate) is a central topic both (1) for the representation of the transfer of momentum at the ocean-atmosphere interface in weather, ocean, wave growth forecasting models, and in coupled models, from sub-meso-scale to climate and paleoclimatic scales, and (2) for spaceborne remote sensing of the wind speed at the surface of the oceans, either in microwaves (mainly scatterometers and radiometers) or in visible wavelengths (observation of foam lines). Our study is focused on the surface air layer that is directly influenced by the presence of waves, which is so-called Wave-influenced Bounday Layer (WBL). After a survey of the existing relations found between wind, momentum, and the surface geometry in gradually increasing wind conditions, we will attempt to relate the results of ongoing fractal analyses based on (1) wind field deduced from PIV technique, (2) horizontal wave slope images from light refraction technique, and (3) Laser slice, in a controlled environment.

How to cite: Bourras, D., Luneau, C., Chemin, R., Bruch, W., Benjeddou, S., and Fraunié, P.: A fractal approach to document the Wave-Influenced Boundary Layer in the Large Air-Sea Interaction Facility of Luminy, Marseille, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14060, https://doi.org/10.5194/egusphere-egu23-14060, 2023.

15:05–15:15
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EGU23-14900
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Highlight
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On-site presentation
Lotfi Aouf, Stephane Law-Chune, Daniele Hauser, and Bertrand Chapron

Ocean waves play a key role in the exchange of heat and momentum fluxes between the ocean and atmosphere, expecially in extreme wind conditions. The availability of directional wave spectra from SWIM lead to a better description of wave systems nearby the trajectories of tropical cyclones as shown recently by Le Merle et al. 2022. Also the assimilation of these directional observations induced an improved forecast of integrated wave parameters and initial conditions from wind-sea to swell propagation. The objective of this work is to examine the impact of the wave-ocean coupling under cyclonic conditions in the Indian Ocean. Coupled simulations between the MFWAM wave model and the NEMO ocean model have performed over the 2020 and 2021 cyclonic seasons in indian ocean. We used an improved wave forcing by assimilating the directional wave spectra and the corresponding significant wave heights provided by the instrument SWIM of CFOSAT satellite. The impact of this enhanced wave forcing on the ocean circulation was compared with the one without CFOSAT data assimilation. The main coupling processes are wave-modified stress, Stokes drift and wave breaking induced turbulence. The results show that wave/ocean coupling leads to a significant increase of the ocean mixed layer along the trajectories of cyclones. This clearly induces a cooling of the upper ocean layers at the rear of the cyclones. The validation of key ocean parameters indicates an improvement in sea surface temperature compared to satellite data (OSTIA). We investigated the currents variability in the upper ocean following the trajectory of cyclone HEROLD. We also examined the impact of the coupling process driven by the wave breaking induced turbulence and investigated a better parametrization than the used one from Craig and Banner (1992). Further conclusions and comments will be discussed in the final presentation of this work.

How to cite: Aouf, L., Law-Chune, S., Hauser, D., and Chapron, B.: On the impact of ocean/wave coupling in tropical cyclones conditions in the Indian Ocean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14900, https://doi.org/10.5194/egusphere-egu23-14900, 2023.

15:15–15:25
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EGU23-17304
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On-site presentation
Alexander Soloviev and Breanna Vanderplow

The sea surface under tropical cyclone conditions is covered by whitecaps and whiteout material. The whitecap areas are formed by large breaking waves and occupy ~4% of the sea surface (Holthuijsen et al. 2012). These areas produce large amounts of bubble and spray but occupy only a relatively small faction of the sea surface. The whiteout material that covers the rest of the sea surface can be caused by shear-induced instabilities of the Kelvin-Helmholtz (KH) type (Soloviev et al. 2017). The KH type instabilities at the gas-liquid interface have been intensively studied in engineering applications such as atomization of the fuel in combustion and cryogenic rocket engines, food processing, and inkjet printing. KH at the air-water interface can take on different forms like ‘fingers’, ‘bags’, ‘mushrooms’, etc. At the air-sea interface KH is additionally modulated by surface waves. In addition, the KH wave at an interface with a large density difference, like the air-water interface, evolves into a strongly asymmetrical shape with all action on the gas side in the form of relatively large spray particles - spume (Hopfner et al. 2011). The sea spray generation function (SSGF) is an input parameter in spray-resolving tropical cyclone forecasting models; however, it is still a major unknown under tropical cyclone conditions. Most of the information on the SSGF for the spume size range comes from the theoretical estimates based on laboratory experiments. The lab measurements are typically conducted above the wave crests and require extrapolation to water surfaces using additional assumptions (Vernon 2015, Ortiz-Suslow et al. 2016, Troitskaya et al. 2018). In this work, we have implemented a computational fluid dynamics (CFD) approach involving a combination of Eulerian and Lagrangian multiphase physics. We have calculated the SSGF function using the ANSYS Fluent Volume of Fluid to Discrete Phase Model (VOF to DPM) including dynamic remeshing. Similar to the laboratory experiments conducted in high-wind speed facilities at Kyoto University, University of Delaware, and University of Miami, the SSGF size distribution of spray particles obtained with VOF to DPM, shows the presence of a significant number of large particles (spume) in major tropical cyclones, which is in contrast to traditional parameterizations. Spume appears to provide the main contribution into the mass, momentum, and energy exchanges at the air-sea interface (Sroka and Emanuel 2022). This is also an indication that spume production is substantially underpredicted by traditional SSGF parameterizations. Importantly, the VOF to DPM extends the SSGF into the range of category 5 tropical cyclone winds, which is still impossible to evaluate even in laboratory conditions. Furthermore, the CFD model provides the “true” SSGF that represents sea spray generation at the air-sea surface and does not require any assumptions as in traditional parameterizations. Implementation of the new SSGF is expected to significantly improve momentum flux, enthalpy flux, and gas flux treatments in tropical cyclone forecasting models in extreme wind speed conditions.

How to cite: Soloviev, A. and Vanderplow, B.: Sea Spray Generation Function Due to Shear-Induced Instabilities of the Air-Sea Interface Under Tropical Cyclone Conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17304, https://doi.org/10.5194/egusphere-egu23-17304, 2023.

15:25–15:35
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EGU23-16204
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Highlight
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On-site presentation
Marc Buckley, Janina Tenhaus, Silvia Matt, and Ivan Savelyev

The ocean surface is, more often than not, riddled with locally generated, growing wind-waves interacting with remotely generated swells. In moderate to high wind speeds, these complex interactions may strongly influence the occurrence of wave breaking as well as airflow separation events, which, in turn, control air-sea fluxes of momentum and scalars.

We present laboratory measurements of air and water dynamics in the vicinity of wind-modulated mechanically generated waves, at a 10 m fetch, using Particle Image Velocimetry. Using flow vorticity and turbulence estimates above and below the waves, we are able to quantify airflow separation and wave breaking events.

We observe modulations of the airflow by locally generated wind waves, including small sheltering events downwind of sharp wave crests. We will discuss the influence of local vs peak wind-wave conditions (e.g., wave age, slope), on wind-wave momentum and energy flux mechanisms.

How to cite: Buckley, M., Tenhaus, J., Matt, S., and Savelyev, I.: Influence of wind-wave/swell interactions on the air-water momentum flux, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16204, https://doi.org/10.5194/egusphere-egu23-16204, 2023.

15:35–15:45
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EGU23-2437
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On-site presentation
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Jie Yu, Mark Orzech, David Wang, Blake Landry, Carlo Zuniga-Zamalloa, and Kathryn Trubac

Marginal ice zones (MIZs) are distinguished by the highly heterogeneous condition of sea ice, e.g., floes of various sizes, pancake, brash and frazil ice, ice ages, brine content, ice thickness and concentration, etc. This makes it challenging to model wave propagation in MIZs, either theoretically or numerically, since there remain similar limitations to mathematically describing such an ice cover on the ocean surface. In this study, we re-consider the problem of linear gravity waves in two layers of fluids with a viscous ice layer overlaying water of deep depth, giving a comprehensive analysis of the fluid velocities, velocity shear, and Reynolds stress associated with wave fluctuations in both the ice layer and the wave boundary layer just beneath the ice. For the turbulent wave boundary layer, water eddy viscosity is used. Speculation of the Eulerian steady streaming is made based on the Reynolds stress distribution, offering a preliminary insight into the wave-induced mean drifts in both the ice layer and wave boundary layer in the water. For wave attenuation, the results using a typical ice viscosity and a reasonable water eddy viscosity show good agreement with data over the range of frequencies for both field and lab waves, significantly outperforming those results assuming an inviscid water. Also discussed are the PIV (particle imaging velocimetry) measurements from the experiment of wave propagation through broken surface ice in a salt water tank in a temperature-controlled facility at the US Army Corps of Engineers Cold Regions Research and Engineering Laboratory (CRREL). Preliminary analysis of the PIV data has provided strong evidence of such a wave boundary layer at the water–ice interface. The measured vertical profiles of fluid velocities and wave-induced Reynolds stress have trends similar to the theoretical predictions, despite the quantitative discrepancies in terms of numerical values. To our knowledge, this is only the second such experiment to measure the three-dimensional fluid velocity fields due to the wave motion under surface ice. This is to be followed by the phase II experiment (scheduled in 2023) in which the ice thickness and other properties will be configured to improve the similitude with field applications. 

How to cite: Yu, J., Orzech, M., Wang, D., Landry, B., Zuniga-Zamalloa, C., and Trubac, K.: Wave boundary layer at the ice–water interface: theory and experiment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2437, https://doi.org/10.5194/egusphere-egu23-2437, 2023.

Posters on site: Wed, 26 Apr, 16:15–18:00 | Hall X5

X5.381
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EGU23-4808
Effects of sea spray on large-scale climatic features over the Southern Ocean
(withdrawn)
Yajuan Song
X5.382
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EGU23-10245
Wu-ting Tsai and Guan-hung Lu

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.

X5.383
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EGU23-10993
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ECS
Siren Rühs, Erik van Sebille, Aimie Moulin, and Emanuela Clementi

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.

X5.384
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EGU23-17107
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ECS
Juan Carlos Guevara Aguirre, Reginaldo Durazo, Héctor García-Nava, Bernardo Esquivel-Trava, Roberto Gomez, and Francisco J. Ocampo-Torres

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.

X5.385
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EGU23-17299
Francisco J. Ocampo-Torres, Pedro Osuna, Nicolas G. Rascle, Héctor García-Nava, Guillermo Díaz Méndez, Bernardo Esquivel-Trava, Carlos E. Villarreal-Olivarrieta, and Rodney E. Mora-Escalante

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.

X5.386
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EGU23-4788
Alexander Babanin

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.

X5.387
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EGU23-1090
Dan Liberzon, Sagi Knobler, Ewelina Winiarska, and Alexander Babanin

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.

X5.388
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EGU23-9740
|
ECS
Eytan Meisner, Dan Liberzon, Mariano Galvagno, David Andrade, and Raphael Stuhlmeier

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.

X5.389
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EGU23-1173
|
ECS
Gang Li, Yijun He, Yang Yang, Guoqiang Liu, Xiaojie Lu, and William Perrie

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.

X5.390
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EGU23-14402
|
ECS
A worldwide coastal analysis of the wave systems
(withdrawn)
Ottavio Mattia Mazzaretto and Melisa Menéndez
X5.391
|
EGU23-2435
Georgy Burde
It is a common situation when asymptotic methods are applied to nonlinear wave problems which involve several parameters assumed to be small. As a canonical example, the classical problem of shallow water waves in ideal fluid may be mentioned. In particular, the famous Korteweg–de Vries (KdV) equation, which is the prototypical example of an exactly solvable soliton equation, was first introduced in the context of that problem. The system of equations describing the long, small-amplitude wave motion in shallow water with a free surface involves two independent small parameters: the amplitude parameter α and the wave length parameter β. No relationship between orders of magnitude of α and β follows from the statement of the problem. In the derivation of model equations, the question of ordering is usually not discussed and it is tacitly assumed that the two small parameters are of the same order of magnitude (the derivation of the KdV equation is the case). However, it is evident that there are no grounds for that assumption and that, in general, the parameters α and β can be not of the same order of magnitude. It is indicated in [1], that, in such a case, a consistent truncation of the asymptotic expansion can be made only on the basis of a prescribed relationship between orders of magnitude of α and β, and a systematic procedure for deriving an equation for surface elevation is developed. The results of the analysis provide a set of consistent model equations for unidirectional water waves which replace the KdV equation in the cases of the nonstandard ordering. The problem of shallow water waves over a slowly varying bottom [2], [3] provides an example of the problem which involves three independent small parameters. As other examples of the problems involving several small parameters, the nonlinear interactions among internal oceanic gravity waves and nonlinear instability of (weakly) nonparallel flows are to be considered.
[1] G. I. Burde and A. Sergyeyev, J. Phys. A: Math. Theor. 46, 075501 (2013).
[2] A. Karczewska, P. Rozmej, and E. Infeld, Phys. Rev. E 90, 012907 (2014).
[3] G. I. Burde, Phys. Rev. E 101, 036201 (2020).

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.

X5.392
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EGU23-11149
Yutaka Yoshikawa, Haruka Imamura, and Yasushi Fujiwara

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.

X5.393
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EGU23-13339
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Simen Å Ellingsen, Benjamin K Smeltzer, Olav Rømcke, and R Jason Hearst

 

The mutual interaction between waves and turbulent currents plays a key role in the energy budget, mixing and mass transfer in the upper layer of the ocean. Turbulence is ubiquitous in the uppermost layer of the ocean, where it interacts with surface waves. Theoretical, numerical, and experimental works (e.g. [1 - 3] and others) predict that motion of non-breaking waves will increase turbulent energy, in turn leading to a dissipation of waves and, potentially, increased mixing and gas transfer between ocean and atmosphere. Conversely, waves encountering a turbulent currents will be scattered and directional seas can suffer a broadening of the directional spectrum [4,5].

In this work we study how the mutual interaction of waves and turbulent flow depends on the properties of the ambient turbulence. The measurements were performed in the water channel laboratory at NTNU Trondheim [6], able to mimic the water-side flow in the ocean surface layer under a range of conditions. An active grid at the inlet allowed the turbulence intensity and length scale to be varied for the same mean flow. The flow field was measured in the spanwise-vertical plane by stereo particle image velocimetry for various background turbulence cases with waves propagating against the current. Scattering was measured with pairs of wave probes at increasing distances from the wave-maker.

A strong increase in streamwise enstrophy (mean-square streamwise vorticity) is observed after vs before the passage of a long, Gaussian wave group. Enstrophy is intensified under troughs and reduced under crests. Scattering is observed, increasing linearly with propagation distance. The scattering rate is found to depend primarily on the energy content at the largest turbulent scales larger than a wavelength, whereas the intensification of turbulence by waves occur at length scales smaller than a wavelength.

[1] Teixeira M. and Belcher S. 2002 “On the distortion of turbulence by a progressive surface wave” J. Fluid Mechanics 458 229-267.
[2] McWilliams J. C., Sullivan P. P. and Moeng C-H. 1997 “Langmuir turbulence in the ocean” J. Fluid Mechanics 334 1-30.
[3] Thais L. and Magnaudet J. 1996 “Turbulent structure beneath surface gravity waves sheared by the wind” J. Fluid Mechanics 328 313-344.
[4] Phillips O. M. 1959 "The scattering of gravity waves by turbulence"  J. Fluid Mech. 5 177-194.
[5] Fabrikant and Raevsky 1994 "The influence of drift flow turbulence on surface gravity wave propagation" J. Fluid Mech. 262 141-156.
[6] Jooss Y., Li L., Bracchi T. and Hearst R.J. 2021 “Spatial development of a turbulent boundary layer subjected to freestream turbulence” Journal of Fluid Mechanics 911 A4.

How to cite: Ellingsen, S. Å., Smeltzer, B. K., Rømcke, O., and Hearst, R. J.: Mutual interactions between waves and turbulence: an experiment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13339, https://doi.org/10.5194/egusphere-egu23-13339, 2023.

Posters virtual: Wed, 26 Apr, 16:15–18:00 | vHall CR/OS

vCO.3
|
EGU23-4824
Ying Bao

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.

vCO.4
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EGU23-6244
|
Highlight
Fangli Qiao

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.

vCO.5
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EGU23-4850
Bin Xiao, Fangli Qiao, Qi Shu, Xunqiang Yin, Guansuo Wang, and Shihong Wang

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.

vCO.6
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EGU23-11366
Sheng Chen

The behavior of drag coefficient (CD) 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 CD is closely related to the location relative to the tropical cyclone (TC) center. The CD  presents an enhancement when the typhoon is away from the observational site. The spatial distribution of CD on the periphery of a TC is asymmetric, and the CD 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 CD can be explained by the differences in wave properties between the two quadrants. CD is smaller in cross-swell conditions than that in the along-wind wave conditions. Observations also confirm that CD tends to level off and even attenuate with the increase of wind speed, and the critical wind speed for CD 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 CD 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.