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OS4.2

Surface Waves and Wave-Coupled Effects in Lower Atmosphere and Upper Ocean

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.

Co-organized by NH5/NP7
Convener: Alexander Babanin | Co-conveners: Fangli Qiao, Miguel Onorato, Francisco J. Ocampo-Torres
Presentations
| Wed, 25 May, 15:10–18:27 (CEST)
 
Room L3

Wed, 25 May, 15:10–16:40

Chairpersons: Alexander Babanin, Lotfi Aouf

15:10–15:17
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EGU22-326
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ECS
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Virtual presentation
Vahid Cheshm Siyahi et al.

A parametric wave model developed by Kudryavtsev et al. (2021) is adapted for Arctic conditions, to help simulate surface waves generated by non-stationary and non-uniform wind fields, to study extreme events in the Norwegian and Barents seas. The ERA-5 reanalysis wind field is used as the input parameter. The model equations are solved using method of characteristics and solutions are then presented as hourly fields of wave parameters (significant wave height, SWH, wavelength, and direction) on the regular grid. The satellite altimeter data are used to validate the model results. Model outputs can then be readily compared with all available satellite observations, including Sentinel-3, Altika and CryoSat-2 measurements.

Observations and analysis of model simulations reveal appearance of abnormal high surface waves, resulting from a resonant fetch-enhancement associated to travelling wind fields.  In other words, the generation of waves in the “spiral-shaped” PLs is most likely associated with the generation of waves in the TCs. However, in PLs with a “comma-shape”, the resonance effect occurs when the strong wind zone inside the PL is located in the right sector, where the direction of the wind velocity coincides with the movement of the front. That is, the surface wave group velocity enters in resonance with moving wind field features, leading to abnormal wave development.

ACKNOWLEDGMENT

The results presented in this work were obtained with the financial support of the Russian Science Foundation, Grant No. 21-47-00038, State Assignment of the Ministry of Science and Education No. 0763-2020-0005 at RSHU, and No. 0555-2021-0004 at MHI RAS.

Reference

Kudryavtsev, V., Yurovskaya M. , Chapron, B., 2021. “2D parametric model for surface wave development in wind field varying in space and time”, Journal of Geophysical Research: Oceans, Vol. 126.

How to cite: Cheshm Siyahi, V., Kudryavtsev, V., and Yurovskaya, M.: Feature of Surface Waves Generated by Polar Lows, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-326, https://doi.org/10.5194/egusphere-egu22-326, 2022.

15:17–15:24
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EGU22-2036
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ECS
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Virtual presentation
Itamar Yacoby et al.

The theory of the transition from an unbalanced initial state to a geostrophically balanced state, referred to as geostrophic adjustment, is a fundamental theory in geophysical fluid dynamics. The theory originated in the 1930s on the f-plane and since then the theory was barely advanced to the β-plane. The present study partially fills the gap by extending the geostrophic adjustment theory to the β-plane in the case of resting fluid with a step-like initial height distribution η0. In the presentation, we focus on the one-dimensional adjustment theory in a zonally-invariant, finite, meridional domain of width L where η0 = η0(y). By solving the linearized rotating shallow water equations numerically, the effect of β on the adjustment process is examined primarily from the wave perspective while the spatial structure of the geostrophic steady-state will be addressed only briefly. The gradient of η0(y) is aligned perpendicular to the domain walls in our zonally-invariant set-up which implies that the geostrophic state only represents the time-averaged solution over many wave periods rather than a steady-state that is reached by the system at long times. We found that: (i) the effect of β on the geostrophic state is significant only for b = cot(φ0)Rd/R ≥ 0.5 (where Rd is the radius of deformation, R is Earth's radius and φ0 is the central latitude of the domain). (ii) In wide domains the effect of β on the waves is significant even for small b (e.g. b=0.005). EOF analysis demonstrates that for b=0.005 and in narrow domains (e.g. L = 4Rd) harmonic wave theory provides an accurate approximation for the waves, while in wide domains (e.g. L = 60Rd) accurate approximations are provided by the trapped wave theory. Preliminary results derived in the two-dimensional case, where η0 = η0(x) is symmetric, imply that the results outlined in item (ii) above hold in this case too. 

How to cite: Yacoby, I., Paldor, N., and Gildor, H.: The structure of waves during Geostrophic Adjustment on the mid-latitude β-plane, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2036, https://doi.org/10.5194/egusphere-egu22-2036, 2022.

15:24–15:31
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EGU22-2064
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ECS
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On-site presentation
Joey Voermans et al.

Material tracers at the ocean surface disperse under the influence of the quasi-random forces that act on the ocean surface. These forces may include ocean turbulence, wind, and surface waves. Currently, wind and ocean turbulence are assumed to be the important drivers of dispersion of the floating tracer particles. Despite some theoretical results and laboratory experiments, the experimental proof of the significant contribution of wave induced dispersion in overall transport of large-scale geophysical systems remains elusive. This is mainly due to a lack of practical observations.

In this study we aim to estimate the contribution of wave-induced dispersion in comparison with conventional mechanisms of dispersion due to ocean turbulence. We do so through the analysis of in-situ observations of surface drifters deployed across the seas and oceans.  The experimental dataset include data from the Global Drifter Program and newly obtained data through cluster deployment of Spotter wave buoys. The results suggest that waves during marine storm conditions may be a critical driver of surface tracer dispersion during the first ten days after the storm and at horizontal length scales up to the order of 10 km. Our results imply that accurate information of wave conditions is required for accurate prediction of tracer dispersion at short to intermediate time and length scales.

How to cite: Voermans, J., Babanin, A., Kirezci, C., Skvortsov, A., Heil, P., Pezzi, L., and Santini, M.: Wave-induced tracer dispersion by ocean surface waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2064, https://doi.org/10.5194/egusphere-egu22-2064, 2022.

15:31–15:38
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EGU22-2741
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ECS
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On-site presentation
Rui Cao and Adrian Callaghan

Bubble plumes within the two-phase flow generated by sufficiently energetic surface breaking waves (whitecaps) enhance the exchange of gas, mass and heat between the atmosphere and ocean. The bubbles formed inside whitecaps range in size from order tens of microns to centimetres, and accurate measurements of the space- and time-evolving bubble size distribution is central to achieving a better understanding of air-sea gas exchange and aerosol production flux.

In the present study, we describe the measurements of time- and space-evolving bubble size distribution in 2-D laboratory breaking waves. The bubbles were measured with high resolution digital images using a range of novel image processing and object detection techniques. A wide range of breaking waves were considered by altering the underlying scale, nonlinearity and spectral bandwidth of the dispersively-focused wave groups. The experiments were initially conducted in the absence of wind, and again under influence of direct wind shear stress. A variety of wind speeds were examined to replicate the effects of varying wave age on the breaking process, air entrainment and resulting bubble size distribution.

Our experimental results demonstrate that underlying wave scale, non-linearity, spectral bandwidth and wind speed (wave age) all have a measurable influence on the evolution of the two-phase flow and bubble size distributions within the breaking waves studied here, highlighting the complexity of the air entrainment over the breaking process. The relative magnitude and importance of these influences will be discussed in detail in this work. For instance, compared to breaking waves without wind stress, wave in the presence of wind tend to break at lower wave steepness, resulting in a reduction of total air entrainment and significantly different spatial distribution of bubbles.

How to cite: Cao, R. and Callaghan, A.: The effects of wave scale, non-linearity, spectral bandwidth and direct wind shear stress on air entrainment and bubble size distributions in laboratory breaking waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2741, https://doi.org/10.5194/egusphere-egu22-2741, 2022.

15:38–15:45
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EGU22-3649
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ECS
Implementation of A WBLM In COAWST and Its Impact on Coastal Storm simulations
(withdrawn)
Jianting Du and Youngzeng Yang
15:45–15:52
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EGU22-3845
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ECS
Evaluation of Assimilation in the MASNUM Wave Model Based on Jason-3 and CFOSAT 
(withdrawn)
Meng Sun et al.
15:52–15:59
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EGU22-3991
Ben Timmermans et al.

Accurate knowledge and understanding of the sea state and its variability is crucial to numerous oceanic and coastal engineering applications, but also to climate change and related impacts including coastal inundation from extreme weather and ice-shelf break-up. An increasing duration of multi-decadal altimeter observations of the sea state motivates a range of global analyses, including the examination of changes in ocean climate. For ocean surface waves in particular, the recent development and release of products providing observations of altimeter-derived significant wave height make long term analyses fairly straightforward. In addition, advances in imaging SAR processing for some missions have made available multivariate observations of sea state including wave period and sea state partition information such as swell wave height. Records containing multivariate information from both Envisat and Sentinel-1 are included in the version 3 release of the European Space Agency Climate Change Initiative (CCI) for Sea State data product.

 

In this study, long term trends and variability in significant wave height spanning the continuous satellite record are intercompared across high-quality global datasets using a consistent methodology. We make use of products presented by Ribal et al. (2019), and the recently released products developed through Sea State CCI. In particular, making use of long term and continuous time series from moored data buoys, we demonstrate the impact of steadily increasing altimeter sample density on trend estimation. In addition to wave height, global climatologies for wave period are also intercompared between the recent Sea State CCI product, ERA 5 reanalysis and in situ observations. Results reveal good performance of the CCI products but also raise questions over methodological approach to multivariate sea state analysis. For example, differences in computational approach to the derivation of higher order summaries of wave period, such as the zero-crossing period, lead to apparent discrepancy between satellite products and reanalysis and modelled data. It is clear that the broadening diversity of reliable sea state observations from satellite, such as provided by the Sea State CCI project, thus motivates new intercomparisons and analyses, and in turn elucidates inconsistencies that have been previously overlooked.

 

We discuss these results in the context of both the current state of knowledge of the changing wave climate, and the on-going development of CCI Sea State altimetry and imaging SAR products.

How to cite: Timmermans, B., Gommenginger, C., and Shaw, A.: Global sea state variability from new multivariate multi-mission satellite altimeter products, reanalyses and wave buoys, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3991, https://doi.org/10.5194/egusphere-egu22-3991, 2022.

15:59–16:06
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EGU22-10814
Francisco J. Ocampo-Torres et al.

There is great interest in acquiring directional ocean surface wave direct measurements in order to better determine sea state conditions in open waters as well as in harbors and nearshore sites. Typical applications range widely over coastal and oceanic engineering, naval architecture and safety at sea, for design and construction of vessels and infrastructure, as well as for maintenance and marine operations. In this work we explore the influence of the buoy motion and we are able to detect some turbulence characteristics of the near surface flow. Full motion of the buoy structure is recorded by an Inertial Motion Unit within the velocimeter case, and after applying motion corrections directional wave and some turbulence characteristics are analyzed. The buoy responde is readily defined and the final results are compared with corresponding measurements from a bottom fixed acoustic Doppler current profiler. Details of the groupinness behaviour of the wave field in a nearshore site are given, showing some enhancement of turbulence intensity during the passage of relatively high wave groups. Some attempts to quantify the kinetic energy dissipation rate are explained. Final results show similar turbulence intensity values from the buoys measurements when compared with those from the fixed ADCP.

How to cite: Ocampo-Torres, F. J., Osuna, P., Esquivel-Trava, B., Rascle, N., and García-Nava, H.: Ocean surface wave and turbulence characteristics from direct measurements with a velocity sensor deployed in a buoy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10814, https://doi.org/10.5194/egusphere-egu22-10814, 2022.

16:06–16:13
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EGU22-4007
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ECS
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On-site presentation
Joseph Peach et al.

Sea surface wave breaking is the dominant process that results in dissipation of ocean surface wave energy. During the breaking process, wave energy is converted into turbulent kinetic energy, and if significantly energetic, entrains air which facilitates air-sea gas transfer and scatters light to create the signature whitecap. Exploiting the broadband scattering of light by the surface whitecaps, this study uses a fixed stereo video system to detect and track individual air-entraining surface breaking waves at wind speeds of up to 16 m/s. The sea surface foam (whitecap) from a breaking event is detected in grayscale images using a brightness thresholding technique based on the image pixel intensity histogram. The movement of individual whitecaps is estimated with optical flow and is used to track whitecaps between consecutive frames. Once breaking events have been tracked through their lifetime, fundamental properties of the whitecap such as the time-evolving foam area [m2], breaking speed [m/s], average crest length [m] and foam area growth and decay timescales [s] are extracted and subsequently aggregated into whitecap statistics. The geometric, kinematic and dynamic quantities obtained for individual whitecaps via this tracking method are used in conjunction with the volume-time-integral method developed in Callaghan et al 2016 to estimate the energy dissipated by each individual whitecap and to then develop an empirical frequency-dependent whitecap energy dissipation source term.

How to cite: Peach, J., Callaghan, A., Bergamasco, F., Benetazzo, A., and Barbariol, F.: Detection and tracking of individual surface breaking waves from a fixed stereo video system, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4007, https://doi.org/10.5194/egusphere-egu22-4007, 2022.

16:13–16:20
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EGU22-6647
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Virtual presentation
Hongyu Ma et al.

Surface gravity waves play an important role in the mixing process of upper ocean. How wave energy is transferred to ocean turbulence through the wave-turbulence interactions remains an open question. Here, laboratory experiments were designed and performed in a wave tank to investigate wave-turbulence interactions in detail. The turbulence intensities before and after the wave-turbulence interactions were compared quantitatively based on their power spectra, and the experimental results indicate that the background turbulence increased approximately by 23.3% through wave-turbulence interaction between 7 and 20 Hz of the power spectrum. Using the Holo-Hilbert spectral analysis method, the results clearly show that the turbulence was modulated by surface waves and then enhanced through the wave-turbulence interaction process. When the wave height was 3 cm and 5 cm, the modulation mainly occurred in the wave trough phase which is consistent with previous literatures. However, the modulation occurred in both the wave trough and crest phases when the surface wave was strong with a wave height of 7 cm. In addition, the intensity of the wave-turbulence interaction increases with the wave height and is proportional to .

How to cite: Ma, H., Dai, D., Jiang, S., Huang, C., and Qiao, F.: Laboratory experimental study on wave-turbulence interactions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6647, https://doi.org/10.5194/egusphere-egu22-6647, 2022.

16:20–16:27
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EGU22-6746
Alexander Babanin

In the presentation, wave-induced influences at the ocean side will be discussed. While the role of breaking waves in producing turbulence is well appreciated, the turbulence produced by wave orbital motion at the vertical scale of wavelength – is not. Such mixing, however, produces feedbacks to the ocean circulation at scales from weather to climate. In order to account for the wave-turbulence effects, large-scale air-sea interaction models need to be coupled with wave models. Theory and practical applications for the wave-induced turbulence are reviewed in the presentation.

 

Analytical approaches for the wave turbulence include viscous and instability theories which appear to be linked. This was verified through direct numerical simulations with fully nonlinear wave model coupled with three-dimensional (LES) model for turbulence. Furthermore, dedicated laboratory experiments and field observations, both in situ and by means of remote sensing, confirmed and validated the conclusions of theory and academic simulations and tests. Finally implementations of the wave-turbulence modules in models for Tropical Cyclones, ocean circulation and sea ice will be demonstrated.

How to cite: Babanin, A.: Wave-induced turbulence, and its role in connecting small- and large-scale ocean processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6746, https://doi.org/10.5194/egusphere-egu22-6746, 2022.

16:27–16:34
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EGU22-6778
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Virtual presentation
Alexander Soloviev et al.

Sea spray is a factor in thermodynamics, intensity, and intensification of tropical cyclones. However, the sea spray generation function under major tropical cyclone conditions is still virtually unknown and the scatter of data between different field experiments is significant. In this work we have conducted a computational fluid dynamics experiment using the approach that has been partially verified with data from the air-sea interaction facility SUSTAIN. In the computational model, the sea spray generation function has been studied using the Volume of Fluid (VOF) method. This method is enhanced with a Volume of Fluid to Discrete Phase transition model (VOF to DPM). Due to dynamic remeshing, VOF to DPM resolves spray particles ranging in size from tens of micrometers to a few millimeters (spume). The water particles that satisfy the condition of asphericity are converted into Lagrangian particles involved in a two-way interaction with the airflow. The size distribution of non-spherical spray particles is represented by the equivalent radii calculated from the particle mass. The sea spray generation function has been calculated for category 1, 3, and 5 tropical cyclones. A comparison with the data available from literature for a category 1 tropical cyclone shows that our sea spray generation function is close to those found by Zhao et al. (2006) and Troitskaya et al. (2018) for the radius range of spume. Our sea spray generation function results in the spray-induced stress exceeding the interfacial wind stress at approximately 60 m/s wind speed. Connection of spray-induced enthalpy flux to the sea spray generation function is more complicated due to the suspension and evaporation of small-size particles in the turbulent boundary layer (Richter’s and Peng 2019 effect of negative feedback).

 

How to cite: Soloviev, A., Vanderplow, B., Lukas, R., Haus, B., Sumi, M., and Ginis, I.: Sea Spray Generation Function in Major Tropical Cyclones, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6778, https://doi.org/10.5194/egusphere-egu22-6778, 2022.

Wed, 25 May, 17:00–18:30

Chairpersons: Alexander Babanin, Francisco J. Ocampo-Torres

17:00–17:10
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EGU22-7300
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solicited
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Highlight
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On-site presentation
Alfred Osborne

The Zakharov equation is a fundamental equation of water waves that is used as a dynamical model for wind wave growth/decay. A nearby Lax integrable version of the Zakharov equation is studied and subsequently a Hamiltonian perturbation provides a close approximation of the Zakharov equation itself.  Theorems of Kuksin, and Baker and Mumford are used to develop the algebraic-geometric solutions of the Zakharov equation in terms of the associated Its-Matveev formula. A subsequent derivation of a multiply periodic Fourier series solution is found which includes the coherent structure solutions (breathers) and cascading. The correlation function is computed and the space/time evolution of the Power spectrum is given analytic form, including a wind-wave transfer function appropriate for multiply periodic Fourier series. Some advantages of this method over classical kinetic equations are that the modulational instability is included together with coherent structure breather solutions. Furthermore, the weak interaction assumptions are no longer necessary in this new formulation, which retains the full nonlinear interactions of the Zakharov equation. 

How to cite: Osborne, A.: The Zakharov Equation as a Model for Wind Waves: Nearby Integrability, Hamiltonian Perturbations and Multiply Periodic Fourier Series, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7300, https://doi.org/10.5194/egusphere-egu22-7300, 2022.

17:10–17:17
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EGU22-7495
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ECS
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On-site presentation
Katja Schultz et al.

This study aims to investigate the wave boundary layer and the turbulent
airflow above wind waves on slick-free and slick-covered water surfaces. To realize
this, we carried out laboratory measurements of the airflow in a wind-wave
tank, where we deployed three surfactants of different visco-elastic properties,
each at five wind speeds ranging from 4 ms−1 to 8 ms−1. For measurements
over slick-free water surfaces, we chose wind speeds, at which we observed the
same peak wave frequencies as in the presence of the surfactants. We measured
high-resolution single-point profiles of the horizontal and vertical velocity
components at different heights above the water surface using a Laser-Doppler-
Velocimeter (LDV), wave heights using a wire gauge, and wave slopes using
a laser slope gauge. Both wave field parameters were recorded simultaneously
with the airflow measurements to investigate the influences of the small-scale
wave field on the wave boundary layer. In the airflow turbulence spectra, we
found a clear maximum corresponding to the dominant wave frequencies reflecting
the influence of the waves on the airflow. However, depending on wind
speed and the surfactants’ damping behaviour, the maximum differs in both its
strength and its height above the wavy surface, the latter being interpreted as
the wave boundary layer height. The LDV achieved mean data rates exceeding
2 kHz; hence, it resolved the small-scale turbulence, which manifests in the
high-frequency part of the turbulence spectra. For the slick-free cases, we observed
a linear decrease in turbulence with increasing height above the surface,
and increasing turbulence with increasing friction velocity u∗, which depends
on the wind speed and wind-wave interactions. However, we did not find clear
trends at any wind speed when the water surface was covered by a surfactant.
Here, the turbulence increases with increasing height above the water surface for
higher friction velocities. Thus, the surfactants dampen not only the waves, but
they also reduce the turbulence in the airflow directly above the waves, within
the wave boundary layer.

How to cite: Schultz, K., Gade, M., Buckley, M. P., and Tenhaus, J.: On the wave boundary layer above wind waves: influence of surfactants, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7495, https://doi.org/10.5194/egusphere-egu22-7495, 2022.

17:17–17:24
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EGU22-7723
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ECS
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On-site presentation
Stina Wahlgren et al.

Antarctic sea ice has an important impact on the global climate, affecting albedo, global circulation and heat- and gas exchange between the ocean and the atmosphere. Wave energy propagating into the sea ice can affect the quality and extent of the sea ice, and wave attenuation in sea ice is therefore an important factor for understanding changes in the ice cover. Yet in-situ observations of wave activity in the Antarctic marginal ice zone are scarce, due to the extreme conditions of the region.

We estimate attenuation of significant wave height in the Antarctic marginal ice zone using in-situ data from two drifting Surface Wave Instrument Float with Tracking (SWIFT) buoys deployed in the Southern Ocean for two days in the Antarctic winter and two weeks in the Antarctic spring. The buoy location ranges from open water to more than 200 km into the sea ice. The extent of the sea ice coverage is determined using satellite sea ice concentration from AMSR-E and SAR imagery from Sentinel-1. Waves were observed more than 150 km into the sea ice, and in higher than 85 % sea ice concentration. Significant wave height and wave direction measured by the buoys in open water agreed well with ERA5 reanalysis data. We find that the significant wave height decayed exponentially in sea ice, which is consistent with physical experiments and other field observations in the Arctic and Antarctic marginal ice zones. 

How to cite: Wahlgren, S., Swart, S., Biddle, L., Thomson, J., and Hošeková, L.: Attenuation of surface waves in the Antarctic marginal ice zone from in-situ measurements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7723, https://doi.org/10.5194/egusphere-egu22-7723, 2022.

17:24–17:31
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EGU22-8355
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ECS
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Virtual presentation
Hector Lobeto et al.

Coastal storms represent powerful and damaging episodes involving climatic variables such as wind, precipitation, sea level and ocean wind waves. Particularly, ocean wind wave storms (or simply wave storms) have a high potential for coastal damage by acting as a major driver of impacts like shoreline erosion and flooding. Wave storms represent extreme wave events significantly exceeding the mean local wave climate conditions, hence impacting the coast by altering the mean equilibrium. This study assesses, for the first time, the global wave storminess based on a high resolution hindcast covering a 42-year period (1979-2020) with hourly time resolution, forced with wind fields from ERA5 reanalysis.

Here, wave events are classified as wave storms by using a unique global criterion based on exceedances over the 95th percentile of the significant wave height. This threshold is selected due to its widespread use in the scientific literature and its flexibility to adapt to local wave conditions, a basic requirement for working at global scale. Additionally, a minimum storm duration of 12 hours and a wave storm independence interval of 48 hours are considered to define the storms. For completeness, an independent analysis of the most severe wave storms reaching the coast is performed. For that matter, wave storms are classified as severe wave storms if the significant wave height exceeds the 99th percentile for more than 6 hours.  

The computation of several statistics and indices allows the analysis of the main characteristics of wave storms, such as frequency, duration and intensity. In addition, the mean significant wave height, mean wave direction and energy flux during wave storms are analyzed. Other secondary storm characteristics, such as swell and wind-sea dominance of the storm energy, and wave height and wave period dominance in the energy transport are also examined to complete the analysis. Results show a global coastal wave storminess pattern strongly characterized by a latitudinal gradient in which the coasts at higher latitudes are stormier than those at lower ones. The higher latitudes show the greatest mean wave heights during storms, reaching over 6 meters in western Ireland or southernmost Chile, and a high number of events per year. The tropical coasts are characterized by lower wave heights and longer storm durations, even exceeding 4 days in some stretches bordering the Arabian Sea. The most relevant exceptions to this behavior in the tropical region are the areas affected by TCs, which can be impacted by storms with very high wave heights.

How to cite: Lobeto, H., Semedo, A., Menendez, M., Lemos, G., Ranasinghe, R., and Dastgheib, A.: On the global assessment of the coastal wave storminess, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8355, https://doi.org/10.5194/egusphere-egu22-8355, 2022.

17:31–17:38
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EGU22-9640
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ECS
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On-site presentation
Lichuan Wu and Fangli Qiao

Air-sea interactions are important for weather and climate predictions since they control the momentum and energy transfer between the atmosphere and the ocean. In current models, the momentum flux in the atmospheric boundary layer is estimated by turbulence closure models which were developed heavily based on measurements over land. However, those turbulence closure models often fail to capture the momentum flux and wind profile in the marine atmospheric boundary layer due to wave impacts. In this study, we proposed a new turbulence closure model to estimate the wind stress in the wave boundary layer from viscous stress, shear-induced turbulent stress, wind-sea induced stress, and swell-induced upward stress, separately. The misalignment between the wind stress and wind is also considered in the model. Single-column simulations indicate that 1) the swell-induced upward momentum flux increases the surface wind and changes the wind direction, 2) the misalignment between the upward momentum flux and wind has a more significant impact on the wind profile than that from the downward momentum flux, and 3) the impact of swell-induced upward momentum flux decreases with atmospheric convection. The proposed closure scheme was implemented into an atmosphere-wave coupled model. A month-long simulation over the ocean off California shows that the surface wind can be altered up to 5% by ocean surface gravity waves.

How to cite: Wu, L. and Qiao, F.: A turbulence closure scheme in the wave boundary layer and its application in a coupled model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9640, https://doi.org/10.5194/egusphere-egu22-9640, 2022.

17:38–17:45
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EGU22-9869
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ECS
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Virtual presentation
Silvio Davison et al.

In recent years, the study of extreme ocean waves has gained considerable interest and several theoretical approaches have been developed for their statistical prediction. However, a full understanding of the main mechanisms responsible for the occurrence of extreme waves has not yet been reached in the relatively common case of a crossing sea, where a local wind sea system coexists with a system of swell. In this context, we investigate how the space-time extreme-value statistics of realistic crossing sea states differs from the statistics of the corresponding short-crested wind sea and long-crested swell partitions during tropical cyclone Kong Rey (2018) in the Northwestern Pacific Ocean (Yellow Sea and East China Sea). The investigation is carried out using an ensemble of numerical simulations obtained from a phase-resolving wave model based on the high-order spectral method (HOSM) and focuses on the maximum sea surface elevation (crest height). The reliability of the numerical model outputs has been assessed with space-time measurements of the 3D sea surface elevation field collected from a fixed offshore platform in the area of interest. Our results highlight the different roles that linear and nonlinear effects have in the formation of extreme waves for different combinations of wind sea and swell systems.

How to cite: Davison, S., Benetazzo, A., Barbariol, F., and Ducrozet, G.: Space-time statistics of extreme ocean waves in crossing sea conditions during a tropical cyclone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9869, https://doi.org/10.5194/egusphere-egu22-9869, 2022.

17:45–17:52
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EGU22-10271
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ECS
Assessing four approximation methods to solve the Boltzmann integral for estimating the transfer of energy due to non-linear interactions in WAVEWATCH III wave model.
(withdrawn)
Leandro Fernandez et al.
17:52–17:59
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EGU22-10856
Effect of high spatial and temporal resolution of the wind field on the evolution of the wave field in a hurricane
(withdrawn)
Pedro Osuna et al.
17:59–18:06
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EGU22-11376
Benjamin K. Smeltzer et al.

Turbulence is ubiquitous in the uppermost layer of the ocean, where it interacts with surface waves. Theoretical, numerical, and experimental works (e.g. [1,2,3] respectively) predict that motion of non-breaking waves will increase turbulent energy, in turn leading to a dissipation of waves. Waves are believed to contribute significantly to the turbulence in the ocean mixed layer, yet additional measurements are needed to validate and distinguish between models and theories [4].

In this work we study the modification of turbulence by surface waves using experimental measurements of turbulent flows in the presence of waves. The measurements were performed in the water channel laboratory at NTNU Trondheim [5], 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 while maintaining an approximately constant 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. The turbulence characteristics are compared to cases without waves, and the turbulence level is found to be increased after the passage of wave groups. The results are discussed considering predictions from rapid distortion theory [1].

 

[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] D’Asaro E.A. 2014 “Turbulence in the upper-ocean mixed layer” Annual Review of Marine Sciences 101-115.

[5] Jooss Y., et al. 2021 “Spatial development of a turbulent boundary layer subjected to freestream turbulence” Journal of Fluid Mechanics 911 A4.

How to cite: Smeltzer, B. K., Hearst, R. J., and Ellingsen, S. Å.: Experimental study of wave-turbulence interaction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11376, https://doi.org/10.5194/egusphere-egu22-11376, 2022.

18:06–18:13
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EGU22-11598
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Highlight
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Virtual presentation
Lotfi Aouf et al.

The climate is evolving rapidly and there is a strong need of better description on momentum and heat fluxes exchanges between the ocean and the atmosphere. Recently directional wave observations from CFOSAT shed ligth on the improvement of dominant wave direction and better scaling of wind-wave growth in critical ocean areas such as the Southern Ocean (Aouf et al. 2021). This work examines the validation of coupled simulations between the ocean model NEMO and the wave model MFWAM including assimilation of directional wave observations. The coupling experiments have been performed for austral summer and fall seasons during 2020 and 2021. The objective of this work is on the one hand to assess the impact of waves on key parameters describing the ocean circulation and on the other hand to evaluate the contributions of different processes of the wave forcing (stress, Stokes drift and wave breaking inducing turbulence) on the mixing in upper ocean layers. The outputs of the coupled simulations have been validated with in situ observations of ocean surface currents, temperature and salinity. The results clearly reveals an improvement in the estimation of the Antarctic Circumpolar Current (ACC) with an increase in the intensity of the current for example in the region between Tasmania and Antarctica. We also observed a significant improvement of the surface currents in the tropics, for instance the ascending brazilian current. In other respects, we have examined the contribution of improved surface stress on inertial oscillations of the current in the Southern Ocean.

Comparison of the surface currents from the coupled simulations with those provided by altimeters showed an increase in current intensity and a better description for small scales in regions of strong currents such as the Agulhas, ACC and Kuroshio regions. We also investigated the impact of wave forcing depending on the mixing layer length.

Further discussions and conclusions will be presented in the final paper.

How to cite: Aouf, L., Law-Chune, S., Hauser, D., and Chapron, B.: On the improvement of surface currents from ocean/waves coupled simulations : Sensitivity to wave forcing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11598, https://doi.org/10.5194/egusphere-egu22-11598, 2022.

18:13–18:20
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EGU22-11717
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ECS
Sophia Brumer et al.

With the flourishing of offshore wind projects there is a new socio-economic interest to better our knowledge and forecasting ability of winds within the coastal marine atmospheric boundary layer (MABL). Air-sea fluxes of enthalpy and momentum greatly influence the turbulent and mean winds in the MABL. Already at moderate but certainly at high winds, wave breaking is a key driver of air-sea fluxes and the sea spray generated by whitecaps is thought to be a crucial component when modelling air-sea interactions. Most studies so far have focused on the role of sea spray in enhancing tropical cyclone intensity.  Here we investigate its impacts on the MABL under strong orographic wind forcing. A coupled model framework was developed within the scope of the CASSIOWPE project aiming at characterizing the physical environment in the Gulf of Lion (NW Mediterranean Sea) in the prospective of future floating wind farms development. It consists of the non-hydrostatic mesoscale atmospheric model of the French research community Meso-NH, the 3rd generation wave model WAVEWATCH III®, and the oceanic model CROCO. Sea-spray physics were incorporated into the Meso-NH’s surface model SURFEX. Added parametrizations will be detailed and a series of test cases will be presented to illustrate how sea spray alters the MABL under Mistral and Tramontane winds. Several sea-state dependent sea spray generation functions (SSGF) are considered in the present study. The variability in simulated fields linked to the choice of wave forcing or coupling will be showcased to evaluate their suitability in varying fetch conditions. Sea spray production remains to be adequately quantified. Existing measurement derived SSGFs span several orders of magnitude resulting in uncertainties in simulated fields which will be discussed.

How to cite: Brumer, S., Bouin, M.-N., Cathelain, M., Leckler, F., Branger, H., Piazolla, J., Veron, F., Michelet, N., Filipot, J.-F., and Redelsperger, J.-L.: Impacts of Sea Spray in a coupled ocean-wave-atmosphere model : Mediterranean Sea case studies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11717, https://doi.org/10.5194/egusphere-egu22-11717, 2022.

18:20–18:27
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EGU22-11735
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ECS
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On-site presentation
Anindita Patra et al.

Wind-waves are of paramount importance for shoreline stability, offshore and coastal activities, and renewable energy generation. There is sufficient evidence of climate-driven trends in historical wave heights. It is important to quantify the relative contributions of natural and anthropogenic forcings to historical changes in wave height in order to produce more reliable future projections and adopt appropriate adaptation strategies. Historical wave climate is simulated using numerical model WAVEWATCH-III ® (WW3) forced by multi-model CMIP6 simulations corresponding to natural forcing only (NAT), greenhouse gas forcing only (GHG), aerosol forcing only (AA), combined all forcings (ALL), and preindustrial control conditions (CTL). Surface wind at 3-hourly temporal resolution, and sea-ice area fraction at monthly frequency, from each CMIP6 model is derived to force spectral wave model WW3 over the global ocean at 1° grid resolution for 1950-2020. Other specification such as spectral discretization and parameterizations is same as the recent WW3 hindcast implemented at Ifremer. The ALL simulations generally ended in 2014, but simulations are extended to 2020 with the SSP (Shared Economic Pathway) 2-4.5 scenario. The preindustrial control (CTL) simulations is used to estimate internal climate variability. Model validation is done using altimeter data set produced by European Space Agency Climate Change Initiative (ESA-CCI), and recent ERA-5 reanalysis. Numerically simulated wave parameters time-series for different external forcing is not available yet. This study produces a novel database particularly useful for investigating the link between wave and climate variability.

How to cite: Patra, A., Dodet, G., and Accensi, M.: Historical Simulation of Global Wave Climate using Anthropogenic and Natural Forcings Derived from Multimodel Ensemble of CMIP6, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11735, https://doi.org/10.5194/egusphere-egu22-11735, 2022.