OS4.1

EDI
Tides in the past, present and future

Tides underlie many processes in the ocean, atmosphere and solid Earth, and influence ocean biogeochemistry and ecosystems. They drive ocean mixing, contribute to coastal erosion and sediment transport, and may provide a renewable energy source. Tides influence coastal infrastructure and safe port operations. The severity of storm surge events and coastal flooding is modulated by tides. The relationship between tides and sea ice is also important, not only for sea ice dynamics, but also for transport and mixing processes in the Arctic and Antarctic regions. Interannual variability in the tides may arise from variations in ice extent, changes in ocean stratification or regional climate processes.

Precise knowledge of tides is also necessary for earth observation where the tides are not the main target of study. They play a significant role in determining high-resolution temporal gravity fields from satellite gravimetry as well as sea-level rise estimations from satellite altimetry. Therefore, understanding the evolution of tides from both models and in-situ observations is necessary to understand the implications of tides in current and future climate estimations.

Observations and models of coastal and internal tides continue to develop, as well as their relationships to wind-driven processes and mixing processes. We welcome submissions on observations and models of surface or internal tides in the context of long-term changes in tides, tidal variability, tidal dynamics and the impacts of tides. Submissions are encouraged both from regional and global-scale studies on all aspects of tides.

Co-organized by G3/NH5
Convener: Joanne Williams | Co-conveners: Stefan Talke, Sophie-Berenice WilmesECSECS, Michael Hart-DavisECSECS, Michael Schindelegger
Presentations
| Mon, 23 May, 13:20–14:50 (CEST), 15:10–15:55 (CEST)
 
Room 1.15/16

Presentations: Mon, 23 May | Room 1.15/16

Chairpersons: Joanne Williams, Michael Hart-Davis
Part I - Tide observations and modelling
13:20–13:30
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EGU22-3944
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solicited
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Virtual presentation
Marta Marcos, Ivan D. Haigh, Stefan A. Talke, Michael Hart-Davis, Denise Dettmering, Philip L. Woodworth, and John R. Hunter

The Global Extreme Sea Level Analysis (GESLA) dataset contains, in its recently released version 3, a total of 5199 tide gauge records of hourly (or higher) temporal resolution, globally distributed and totalling more than 91000 years of data (www.gesla.org). This represents twice the number of observations compared to the former version of the database. The tide gauge records have been compiled from multiple data providers and so they have different levels of quality controls. Here we describe a set of tools to homogenise and quality control sea level observations from raw GESLA files, including adjustments of datum jumps and time shifts in the time series. We apply these tools to estimate tidal constituents from the extended in-situ dataset. The results are used to identify the river influences on coastal tide gauges and to map the spatial patterns of mean tidal ranges along densely monitored coastlines.

How to cite: Marcos, M., Haigh, I. D., Talke, S. A., Hart-Davis, M., Dettmering, D., Woodworth, P. L., and Hunter, J. R.: The new GESLA-3 tide gauge data set and its quality control for tidal studies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3944, https://doi.org/10.5194/egusphere-egu22-3944, 2022.

13:30–13:37
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EGU22-9396
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Virtual presentation
Elizabeth Bradshaw, Andrew Matthews, Simon Williams, and Angela Hibbert

The Permanent Service for Mean Sea Level (PSMSL) is the internationally recognised global sea level data bank for long-term sea level change information from tide gauges, responsible for the collection, publication, analysis and interpretation of sea level data. There is a need both for more records in data sparse regions such as Antarctica, the Arctic and Africa, and for a low cost method for monitoring climate change through sea level. 

While tide gauge sensors themselves are not very expensive, the costs in operating them over a long period of time can be considerable. Sensors based in the water are prone to biofouling, and can require divers to access. Meanwhile, land-based sensors are exposed to damage from accidents, storms, and vandalism. 

The emerging field of GNSS (Global Navigation Satellite Systems, such as GPS, GLONASS, Galileo and BeiDou) interferometric reflectometry (GNSS-IR) provides an alternative way to measure sea level. Permanent GNSS receivers are routinely installed near the coast to monitor land movements, and we can infer sea level by comparing the direct signal to a GNSS with those reflected off the surface of the water. GNSS-IR does not yet match the accuracy of traditional tide gauges, but has the potential to be part of an affordable, effective monitoring system of water levels. 

Here we present a new data portal of sea level measured using GNSS-IR, developed as part of the EuroSea project. So far, we have extracted sea level data from over 250 GNSS receivers worldwide. At each site we provide a file of calculated sea levels, along with metadata about the site, some diagnostic plots, and links to the source of the original GNSS data. We have also created an interactive map to help investigate the footprint of a GNSS installed at any location. 

At present the portal is in a beta stage of development, and we hope to continue to make improvements, including hosting the data on a server with an API (ERDDAP) to allow interoperable access to data and metadata in a wide range of formats. We have carried out proof-of-concept tests that demonstrate that data can be provided in near real time, and aim to secure funding to allow us to add this in the future. 

How to cite: Bradshaw, E., Matthews, A., Williams, S., and Hibbert, A.: A new service providing sea level height data using GNSS sensors from around the globe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9396, https://doi.org/10.5194/egusphere-egu22-9396, 2022.

13:37–13:44
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EGU22-740
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On-site presentation
Joanne Williams, Andrew Matthews, and Elizabeth Bradshaw
How can you get sea-level data faster than one day at a time? Get it from the past!
 
The port of Liverpool is one of the world's longest sea-level records, but for the 1800s the only digital record is hand-calculated monthly mean data, which have many gaps. Hand-written ledgers contain high frequency (15 minute) records from 1853 to 1903, both at Liverpool and neighbouring Hilbre Island. In 2021, we coordinated over 3600 volunteers through the Zooniverse website to transcribe this data. At the time of writing this abstract, the transcription is nearing completion.  From the newly digitised data we can examine whether tides in the Mersey have changed and reassess the frequency of rare storm surge events. We now understand the reason for the gaps in the Liverpool monthly mean sea-level, which are due to a dock fire and an intermittent siltation problem at low water, and may be able to use the Hilbre data to help fill them.
 
We report on the feasibility of this process for other transcription projects, the unusual quality control requirements for volunteer transcription, and present the newly restored data with 19th Century tides, storm surges and sea-level.
 

How to cite: Williams, J., Matthews, A., and Bradshaw, E.: Using citizen science to digitise 3 million hand-written tide-gauge data entries, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-740, https://doi.org/10.5194/egusphere-egu22-740, 2022.

13:44–13:51
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EGU22-9505
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ECS
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On-site presentation
Jelmer Veenstra, Sanne Muis, and Martin Verlaan

The Global Tide and Surge Model (GTSM) is a depth-averaged hydrodynamic model, developed by Deltares. GTSM can be used to dynamically simulate water levels and currents, that arise from tides and storm surges. The model is based on Delft3D Flexible Mesh software and has a spatially varying resolution which increases towards the coast. Previous studies with this model used GTSMv3.0 and focused for instance on operational forecasting, reanalysis and climate projections and estimation of return periods (Muis et al., 2020; Dullaart et al., 2021), satellite altimetry (Bij de Vaate, 2021), changes in tides due to sea level rise and various others.

Significant improvements in model performance were made in the newest GTSMv4.1, released in 2021. This model with increased resolution and improved representation of physical processes was calibrated by applying bathymetry and friction correction (Wang et al., 2021). From GTSMv3.0 to GTSMv4.1, the model performance showed great improvements with a 37% reduction of the root-mean-squared-error between modelled and observed tides from 17.8 cm to 11.3 cm.

The model development is an ongoing and continuous effort. The current developments are to improve the grid+bathymetry, representation of the sea-land interface, improving the spatial distribution of internal tide energy dissipation and the inclusion of other baroclinic processes like steric and radiational tides. Preliminary results show improvements in several areas. Furthermore, improving geometry representation by cutting parts of coastal cells with a landboundary often shows to improve the model performance just as significant as a resolution increase, while saving computational cost.

How to cite: Veenstra, J., Muis, S., and Verlaan, M.: Developments of the Global Tide and Surge Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9505, https://doi.org/10.5194/egusphere-egu22-9505, 2022.

13:51–13:58
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EGU22-4695
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ECS
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On-site presentation
Lana Opel and Michael Schindelegger

Low-frequency non-astronomical changes of tides are among the most puzzling signals in the world ocean. Although the relevance of these signals in the order of a few cm is gradually being appreciated in the context of coastal flooding or de-aliasing of satellite gravimetry observations, a detailed quantitative understanding of the causative mechanisms has been lacking. Among the suspected forcing factors are fluctuations and trends in relative sea level, basin geometry (associated with, e.g., melting Antarctic ice-shelves), bed roughness, and ocean stratification. Here, we use a high-resolution general circulation model to spatially map the influence of stratification changes on the global M2 tide, on time scales from years out to decades. We conduct global tidal simulations in annually changing density structures, as drawn from hydrographic profiles and other external datasets (e.g., an eddying ocean reanalysis) from 1993 to present day. We perform internal-tide permitting simulations (1/12° horizontal grid spacing, 50 vertical layers) to resolve the relevant physics, particularly low-mode barotropic-to-baroclinic energy conversion at topographic features and vertical mixing in shallow water. Atmospheric forcing is omitted to constrain the model’s density distribution to the prescribed initial hydrography. We validate the resulting annual M2 amplitude changes against estimates from harmonically analyzed tide gauge series, distributed across the globe. Particular emphasis in our analysis is given to the tropical Pacific and the South China Sea, where the seesawing of stratification between positive and negative phases of ENSO (El Niño-Southern Oscillation) is expected to introduce spatially coherent amplitude modulations of ±1 cm on interannual time scales.

How to cite: Opel, L. and Schindelegger, M.: Modeling the impact of contemporary ocean stratification changes on the global M2 tide, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4695, https://doi.org/10.5194/egusphere-egu22-4695, 2022.

13:58–14:05
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EGU22-12362
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ECS
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Virtual presentation
Andrei A. Dmitrovskii, Hilary Martens, Amir Khan, Martin van Driel, and Christian Boehm

Deformations of the solid Earth as a response to ocean tidal loading (OTL) are sensitive to the material properties of Earth’s interior across a broad range of spatial and temporal scales. Studying tidal response can provide constraints on the interior structure, which are complementary to seismic tomography and particularly important to explore the interior response to low frequency loads. Although seismic tomography is widely used to constrain the Earth’s interior, it is prone to be only slightly sensitive to the density distribution in the interior with an increase of the sensitivity towards the long period signal. Whereas previous research (e.g. Ito & Simons, 2011, Martens et al., 2016) has shown that the tidal surface displacements may be sensitive to elastic properties of the interior to the same extent as to the mass distribution in the lithosphere and the mantle. The latter are of massive interest to all fields of geophysics and especially geodynamics.

We present a numerical approach to simulate the elastic and gravitational responses of the solid Earth that relies on the spectral-element method. Modeling the governing equations in a 3-D Earth using a coupled system of the elastostatic and Poisson’s equations enables us to include effects like topography or lateral variations in Earth structure. The adjoint method is a powerful technique to simultaneously compute sensitivity with respect to all material parameters, e.g., density and elastic moduli, by solving an auxiliary linear system. We introduce a recipe for computing adjoint-based sensitivities of the complex-valued amplitude of surface displacement by two simulations for the real and imaginary part of the surface load. Those two simulations are independent under assumption of negligible attenuation.

How to cite: Dmitrovskii, A. A., Martens, H., Khan, A., van Driel, M., and Boehm, C.: Adjoint modeling of load-tide sensitivity , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12362, https://doi.org/10.5194/egusphere-egu22-12362, 2022.

14:05–14:12
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EGU22-2478
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ECS
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On-site presentation
Michael Hart-Davis, Roman Sulzbach, Denise Dettmering, Maik Thomas, Christian Schwatke, and Florian Seitz

Satellite altimetry observations have provided a significant contribution to the understanding of global sea surface processes, particularly allowing for advances in the accuracy of ocean tide estimations. Accurate estimations of ocean tides are valuable for the understanding of sea surface processes from along-track satellite altimetry. Ocean tide models have done a suitable job in providing these estimations, however, difficulties remain in the handling of minor tidal constituents. The estimation of minor tides from altimetry-derived products proves difficult due to the relatively small signals of these tides and due to the temporal sampling of the altimetry missions meaning a long time series of observations is required. This is generally solved by models and tidal prediction software by using admittance theory to infer these minor constituents from the more well-known and better estimated major constituents. In this presentation, the results of a recent study that looked at the estimation of several minor constituents directly from tide models compared to the inferred version of these tides are presented. The model used for the direct estimations and the inferences is a regional version of the Empirical Ocean Tide model (EOT) which is a data-constrained model derived from multi-mission satellite altimetry. The resultant estimations from these two approaches are compared to two global numerical tide models (TiME and FES2014) and in situ tide gauge observations (from the TICON dataset). Based on the study of eight tidal constituents, a recommendation of directly estimating four tides (J1, L2, μ2 and ν2) and inferring four tides (2N2, ϵ2, MSF and T2) is given to optimise the ocean tidal correction. Following on from this, a new approach of merging tidal constituents from different tide models to produce the ocean tidal correction for satellite altimetry that benefits from the strengths of the respective models is presented. This concept allows for the benefit of using data-constrained tide models in the estimation of the major constituents as well as the use of numerical models in providing a greater number of minor constituents, to be combined to provide a more optimised estimation of the full tidal signal.

How to cite: Hart-Davis, M., Sulzbach, R., Dettmering, D., Thomas, M., Schwatke, C., and Seitz, F.: The assessment of minor tidal constituents in ocean models for optimising the ocean tidal correction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2478, https://doi.org/10.5194/egusphere-egu22-2478, 2022.

14:12–14:19
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EGU22-4019
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ECS
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On-site presentation
Hannah Sophia Davies, J. A. Mattias Green, Dave Waltham, and João C. Duarte

The supercontinent cycle and Wilson cycle describe the periodic formation and termination of supercontinents and ocean basins respectively. This cyclicity has occurred since the beginning of the Phanerozoic, however, it may have been active in some form much earlier (i.e., during the Proterozoic). The periodic opening and closing of ocean basins following the Wilson cycle has been found to affect the tides, as oceans grow and shrink over geological time, they occasionally allow open ocean tidal resonance to occur. These resonant periods are relatively short lived (~ 20 Ma) however, they profoundly affect the tidal energy budget of the planet while active.  

We have now investigated the relationship between tides and “plate tectonics” during the Archean, Paleo-Proterozoic, Cryogenian, Ediacaran, Devonian, and during conceptualised future supercontinent scenarios. We find that periods of open ocean tidal resonance occur much more frequently in our tidal models after ~600 Ma. While earlier periods of Earth history where the Moon was physically closer produce higher relative tides, later periods such as the Ediacaran, Devonian and present day produce higher tides through open ocean resonance. This trend continues into the near future, with open ocean resonance likely occurring multiple times before the formation of the next supercontinent. Notwithstanding, the Cryogenian period represents an outlier in this trend, with very low tidal dissipation rates. We conclude that this is due to the global “snowball” glaciations of the time supressing the tide. Despite the Cryogenian outlier, our results are consistent with other deep-time modelling studies.

The result of the Cryogenian, and the disparity in time between periods which we have tidally modelled, show that more work is needed to fully reconstruct the tidal environment of the Earth in deep-time. Filling in the missing periods with tidal modelling efforts and including the effect of other components of the Earth system, (i.e., glacial periods/climate, orbital parameters, and tectonic setting) are all needed to establish a robust record of the tide in deep-time. This can then be further validated with other models and geological data of the tide to help us better understand Lunar orbital evolution, and the Earth system in the past and potentially in the future.

How to cite: Davies, H. S., Green, J. A. M., Waltham, D., and Duarte, J. C.: Tides And Relative Dissipation In Supercycles – An overview of tidal modelling work with OTIS and what’s next., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4019, https://doi.org/10.5194/egusphere-egu22-4019, 2022.

14:19–14:26
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EGU22-9241
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On-site presentation
Roman Sulzbach, Volker Klemann, Henryk Dobslaw, Gregor Knorr, Gerrit Lohmann, and Maik Thomas

Ocean tidal dynamics depend on several factors of which some have experienced considerable changes since the last glacial maximum (LGM). Mainly driven by deglaciation-induced sea-level rise and altered oceanographic conditions, these changes comprise (i) the global bathymetric conditions that control ocean tide resonances, (ii) shallow-water energy dissipation in shelf seas, (iii) deep-ocean energy dissipation by internal wave drag, and (iv) sea-ice energy dissipation affected by the reduced sea-ice coverage. The corresponding changes in tidal range and energy dissipation (e.g., Wilmes and Green, 2014) with respect to modern-day tidal conditions are important for reconstructing paleo-oceanographic conditions with a direct impact on paleoclimatic simulations and, e. g., the interpretation of sea-level markers that depend on the actual tidal range.

In this contribution, we present paleo tidal simulations obtained with the purely hydrodynamic ocean tide model TiME2021 (Sulzbach et al. 2021), which was updated with a sea-ice friction parametrization. Applying bathymetry changes due to glacial isostatic adjustment and internal dissipation changes due to paleo ocean stratification and paleo sea-ice coverage, we find the latter effect (iv) to be of minor importance. For a timespan ranging from modern-day conditions to 21 ky before present, simulations were performed on a rotated numerical grid that ensures high accuracy in the Pan-Arctic region which is known to have drastically changed in the semidiurnal tidal regime from micro- to mega-tidal (e.g., Velay-Vitow and Peltier, 2020). We find the phenomenon of Arctic Megatides being highly sensitive to the employed parametrization of Self-Attraction and Loading (SAL), which can be locally approximated or included to full extent by considering a global load Love number approach. For a cylindrical, analytical model of the Arctic basin, the observed behavior of the Arctic tidal regime can be directly related to properties of the lowest-order Arctic Kelvin wave, so, it can be traced back to bathymetric changes.

In line with other studies, we find tidal energy dissipation especially in the deep ocean to be strongly increased during the LGM. We further present charts for different epochs displaying relative changes in the tidal range with respect to modern conditions that show deviations of several meters in critical regions (Arctic Ocean, South China Sea, Baffin Bay). The employed approach is based on simulations of two major partial tides per tidal band (M2, K2 and O1, K1) and the linear admittance theory. This information is aimed to be used with sea-level markers that are sensitive to tidal levels in order to improve the consistency of paleo sea-level reconstructions.

 

References:

[1] Wilmes S. B. and Green J. A. M. (2014), JGR: Oceans, 119, 4083–4100

[2] Sulzbach, R., Dobslaw, H., & Thomas, M. (2021), JGR: Oceans., 126, 1–21

[3] Velay-Vitow, J. and Peltier, W. R. (2020), Geophysical Research Letters, 47, e2020GL08987

How to cite: Sulzbach, R., Klemann, V., Dobslaw, H., Knorr, G., Lohmann, G., and Thomas, M.: Relative Changes in Tidal Ranges on the Northern Hemisphere since the Last Glacial Maximum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9241, https://doi.org/10.5194/egusphere-egu22-9241, 2022.

14:26–14:33
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EGU22-9980
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ECS
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On-site presentation
Sophie-Berenice Wilmes and J. A. Mattias Green

Simulations of the tides from the Last Glacial Maximum (26.5 – 19 kyr BP) to the present show large amplitude and dissipation changes, especially in the semi-diurnal band during the deglacial period. New reconstructions of global ice sheet history and sea levels allow us to extend the tidal simulations back to cover most of the last glacial cycle. Climate during this period was far from stable with periods of ice sheet advance and lower sea levels interspaced with ice sheet melting and sea level increases. Here, using the sea level and ice history from Gowan et al., 2021, we present simulations of tidal amplitudes and dissipation from 80 kyr BP to present using the tide model OTIS. Our results show large variations in amplitudes and dissipation over this period for the M2 tidal constituent with several tidal maxima. Due to the lower sea levels and altered bathymetry open ocean dissipation was enhanced with respect to present day levels for most of the glacial cycle. This result is important in the context of historical ocean mixing rates. For the semi-diurnal K1 tide, in contrast, changes are mainly local or regional. 

How to cite: Wilmes, S.-B. and Green, J. A. M.: Evolution of tides and tidal dissipation over the last glacial cycle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9980, https://doi.org/10.5194/egusphere-egu22-9980, 2022.

14:33–14:40
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EGU22-8346
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ECS
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Virtual presentation
Arina Korzhenovskaia, Igor Medvedev, and Viktor Arkhipkin

The Sea of Azov is the most isolated and shallow sea of the World Ocean. Longterm hourly data from 14 coastal tide gauges were used to study the features of tides in the Sea of Azov. Spectral analysis showed well-defined spectral peaks at tidal diurnal and semidiurnal frequencies. Harmonic analysis of tides for individual annual sea level series with consecutive vector averaging over the entire observation period was applied to estimate mean amplitudes and phases of 11 tidal constituents. The amplitude of the major diurnal harmonics is generally greater than the semidiurnal ones. The amplitude of the diurnal radiational constituent S1 changes from 6 cm at the head of the Taganrog Bay to 0.5 cm in the Kerch Strait, while the amplitude of the main semidiurnal gravitational harmonic M2 inside the sea varies from 1.0 cm in the southeastern part of the Sea of Azov, to 0.38 cm at Mysovoye. The tidal form factor within the Sea of Azov changes significantly from the diurnal form in the north to the mixed, mainly semidiurnal near the Kerch Strait. The maximum theoretical tidal range of 19.5 cm were found at the head of the Taganrog Bay, and the lowest was noted in the Kerch Strait, 4.9 cm. The assumption about the predominantly radiational genesis of diurnal tides is confirmed by the seasonal variations of their spectrum. Radiational tides in the Sea of Azov may be initiated by sea breeze winds, which is best expressed in summer.

How to cite: Korzhenovskaia, A., Medvedev, I., and Arkhipkin, V.: Tidal sea level oscillations in the Sea of Azov, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8346, https://doi.org/10.5194/egusphere-egu22-8346, 2022.

14:40–14:50
Coffee break
Chairpersons: Sophie-Berenice Wilmes, Joanne Williams
Part II Internal Tides and Global Circulation
15:10–15:17
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EGU22-7405
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ECS
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On-site presentation
Gaspard Geoffroy, Jonas Nycander, and Casimir de Lavergne

A global map of the amplitude of the semidiurnal internal tide at the 1000 dbar level, obtained from Argo park-phase data, is converted to depth-integrated energy density. As opposed to current satellite altimeter data, the high sampling rate of the floats enables the direct observation of the total wave field, including waves with a time varying phase difference to the astronomical forcing. Thus, the Argo-derived energy content is only affected by mixing, scattering, and nonlinear processes. The Argo data alone do not allow for retrieving the distribution of the energy over the different vertical modes. Nevertheless, the modal partitioning of the Argo-derived energy content is inferred from other datasets. The results are compared with a geographical distribution of the internal tide energy content estimated with a Lagrangian ray tracing model. The outcome is in turn used to tune the modelled attenuation of low-mode internal tides.

How to cite: Geoffroy, G., Nycander, J., and de Lavergne, C.: Energy of the semidiurnal internal tide from Argo data compared with theory, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7405, https://doi.org/10.5194/egusphere-egu22-7405, 2022.

15:17–15:24
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EGU22-1159
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On-site presentation
Jonas Nycander and Friederike Pollmann

Breaking internal tides contributes substantially to small-scale turbulent mixing in the ocean interior and hence to maintaining the large-scale overturning circulation. How much internal tide energy is available for ocean mixing can be estimated by using semi-analytical methods based on linear theory. Until recently, a method resolving the horizontal direction of the barotropic-to-baroclinic energy transfer was lacking. We here present the first global application of such a method for the first vertical mode of the principal lunar semi-diurnal tide. The conversion rate estimates are in general agreement with those obtained in previous studies, albeit somewhat smoother since the non-locality of the internal tide generation problem is taken into account more strongly. An advantage is that the conversion rate is positive definite with the new method. We also show that the effect of supercritical slopes on the modally decomposed internal tides is different than previously suggested. To deal with this the continental shelf and the shelf slope are masked in the global computation. The result shows that the energy flux can vary substantially with direction depending on the shape and orientation of topographic obstacles and the flow direction of the local tidal currents. Taking this additional information into account in tidal mixing parameterizations could have important ramifications for vertical mixing and water mass properties in global numerical simulations.

How to cite: Nycander, J. and Pollmann, F.: Resolving the horizontal direction of internal tide generation: Global application for the first mode M2-tide, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1159, https://doi.org/10.5194/egusphere-egu22-1159, 2022.

15:24–15:31
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EGU22-1644
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ECS
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On-site presentation
Joseph Elmes, Stephen Griffiths, and Onno Bokhove

Approximately 70% of the global dissipation of the barotropic tide occurs in the waters of the continental margins, due to bottom friction on the shelves and internal tide generation at the continental slopes. Here we are interested in the latter process, and how it depends upon the presence of submarine canyons, which are a ubiquitous feature of continental slopes. Whilst there have been modeling studies of internal tide generation at particular canyons (e.g., Monterey), our emphasis is on understanding the effects of canyon geometry more generally, given the diversity of canyons that exist across the globe.  

To do this, we study idealised canyon configurations cutting through idealised continental slopes, enabling us to define and then explore a relevant parameter space (canyon length, width, depth, etc.). For forcing by a prescribed barotropic tide, taking the form of a Kelvin wave with predominantly alongshore flow, we investigate both the amplitude and direction of the implied radiating internal tides, and generate scaling laws for how the tidal dissipation varies across parameter space.

Such a study would be challenging and extremely time consuming with traditional ocean circulation models, because of the small length scales of both the canyons and the internal tides. For efficiency, we thus use the multi-modal linear modelling strategy of Griffiths and Grimshaw (2007), but solved with cutting-edge numerics in the form of a Discontinuous Galerkin Finite Element methodology. We have generated high-quality multi-scale triangular meshes to resolve the canyons, and can deploy a range of test-function orders and numerical fluxes therein. This methodology is a key part of this study.

How to cite: Elmes, J., Griffiths, S., and Bokhove, O.: Internal Tide Generation by Submarine Canyons, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1644, https://doi.org/10.5194/egusphere-egu22-1644, 2022.

15:31–15:38
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EGU22-10432
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ECS
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On-site presentation
Federica Borile, Simona Masina, Doroteaciro Iovino, Nadia Pinardi, and Paola Cessi

The energy budget of the global ocean circulation highlights the importance of winds and tides as main sources of energy. As wind forcing acts at the ocean surface, tidal potential affects the entire water column and, in regions of rough topography, it generates energy conversion from barotropic to baroclinic high frequency modes. An intercomparison is computed between experiments with and without tidal forcing, using a global ocean general circulation model in two different configurations, respectively mesoscale-permitting and mesoscale-resolving ones. Regardless of the resolution, the contribution of tides to the mean kinetic energy is negligible on the global scale, while it enhances the eddy kinetic energy, especially on continental shelves and rough bottom topography sites, where internal waves are generated before being dissipated or radiated away. The interaction between these waves and mesoscale features is enhanced in the higher-resolution experiments, and their effects on the mean circulation are analysed in two regions where the tidal activity is well documented: the North-West Atlantic Ocean and the Indonesian region. We investigate the impact of internal tides presence on the modelled tidal amplitude, and we include a topographic wave drag as an additional term of internal wave dissipation.

How to cite: Borile, F., Masina, S., Iovino, D., Pinardi, N., and Cessi, P.: Tidal effects in a global general circulation model: comparison between coarse and high resolution configurations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10432, https://doi.org/10.5194/egusphere-egu22-10432, 2022.

15:38–15:45
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EGU22-10852
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ECS
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Virtual presentation
Jeffrey Uncu and Nicolas Grisouard

Internal tides (ITs) are internal waves which oscillate at the tidal frequencies. ITs may cross entire ocean basins and along the way, they may be redirected, break, and dissipate. The latter is due to changes in stratification, bottom turbulence, wave-wave interactions, and of interest in this study, the scattering of ITs by balanced flow. Mesoscale wave-vortex interactions are characterized by low Rossby numbers. With the aid of satellite altimetry, the effects of mesoscale eddies on ITs has been used successfully to map low mode IT propagation.  In the submesoscale, these interactions become more complex, due to strong non-linearities, a partial breakdown of geostrophic balance, and intermediate scales for both balanced flows and ITs, which are hard to observe with current methods. However, the next generation of satellite altimetry, the Surface Water and Ocean Topography mission, will have fine enough resolution to begin to capture the submesoscale, which makes it an exciting time to explore wave-vortex interactions in this regime. We use the one-layer shallow water model to run idealized numerical simulations of a single wave mode propagating through a (cyclo)geostrophic vortex. By varying the Rossby number, which controls the strength of the vortex, and varying the relative scale of the vortex size to IT wavelength, we observe the IT energy redistribution at the lee side of a submesoscale vortex. We find that high Rossby numbers and relatively small waves will induce sharper deflections in wave propagation, which we quantify with energy flux calculations. By applying complex demodulation, we can filter the incoming plane wave to reveal the characteristic pattern of an isolated vortex scatter, which consists of three beams, two slightly skewed beams from the edge of the vortex, and one strongly skewed beam from the middle.

How to cite: Uncu, J. and Grisouard, N.: Internal Tide Scattering by an Isolated Cyclogeostrophic Vortex, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10852, https://doi.org/10.5194/egusphere-egu22-10852, 2022.

15:45–15:55