Oceanographic processes at coastal scales present a number of differences with respect to deep water oceanography, which result in higher prediction errors. In shallow water coastal domains the bottom topography exerts a strong control on the resulting wave/current fields and other factors need to be accounted for (stratification and mixing effects, land boundary condition). Moreover, the coupling between wind, waves, currents and sediments at limited scales, or even the choice of numerical strategy (nested meshes, finite-elements, etc.) may also play a critical role in the quality of the predictions. Coastal observations are therefore necessary to drive numerical models, combining in-situ data and satellite images. The advent of new satellite capabilities (resolution and sensors like for instance those of the Sentinel constellation) and new modelling advances (coupling and boundary conditions) with coastal observatories should allow starting a quantum leap in coastal oceanography.

These issues are even more relevant in a framework of changing climate, since coastal and transitional areas are strongly impacted by climate. Because of these reasons, it is timely to discuss recent advances in fields such as: integrated ocean-atmosphere-sediment modelling approaches and the physics of their coupling mechanisms; the hydrological, biogeochemical, geomorphological variability of coastal regions; the availability and use of coastal in-situ observations; and standards, procedures and data formats to make data ready for use in an integrated coastal ocean monitoring system. Following this, some of the themes we invite for this session are satellite/in-situ measurements, coastal assimilation, atmosphere-ocean-sediment model coupling and error/prediction limits as well as the contribution of coastal ocean science to operational oceanography. Finally, how these main processes control coastal variability (hydrodynamics, morphodynamics and bio-geochemical processes) and applications to improve our knowledge on how these processes interact with coastal infrastructure or activities.

Convener: Agustín Sánchez-Arcilla | Co-conveners: Davide Bonaldo, Sandro Carniel, Manuel Espino Infantes, Emil Stanev
| Attendance Tue, 05 May, 08:30–10:15 (CEST)

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Chat time: Tuesday, 5 May 2020, 08:30–10:15

D2752 |
Guillaume Koenig, Clément Aldebert, Cristèle Chevalier, and Jean-Luc Devenon

If lateral boundary conditions are crucial for physical modelling of the ocean dynamics, their estimate may lack of accuracy in coastal regions. Data-assimilation has been a long-used tool to improve accuracy, but most of the existing popular methods are difficult to implement. To solve this, we tried a new and an easy-to-implement method to estimate boundary conditions. This method uses data assimilation with a stochastic gradient descent  and successive approximations of the boundary conditions. We  tested it with twin experiments on a tidal model in the lagoon of Ouano, in New-Caledonia. The method was successful and provided robust estimation of the boundary conditions with various settings of subsampling and noise for the pseudo-data. Here we present those results and discuss about how the stochastic gradient descent and the approximations have to be tuned.

How to cite: Koenig, G., Aldebert, C., Chevalier, C., and Devenon, J.-L.: A new tool for identifying boundary conditions in coastal oceanic models : First tryouts with a tidal model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9250, https://doi.org/10.5194/egusphere-egu2020-9250, 2020.

D2753 |
| Highlight
Miguel Agulles and Gabriel Jordà

In recent years there have been endless coastal actions that have substantially modified the equilibrium conditions of much of the coastline. This fact, along with an unprecedented coastal population growth and the projected sea level rise, make beaches a particularly vulnerable region to climate change impacts. In particular, there is a clear need to quantify the reduction of the beach area due to the combination effects of the sea level rise and changes in the waves in the swash zone, under different future climate scenarios.

In this work different methodologies are developed to estimate the retreat of the coastline and to quantify the associated uncertainties. The methodologies have been applied to three beaches of the Balearic Islands, which have been continuously monitored during the last decade. The different methodologies imply the use of models to propagate the waves from deep waters to shallow depths and to compute wave runup. The results are compared to simpler approaches based on empirical formulations that provide a cost-effective solution to cover large domains. All the different approaches are validated with coastal wave recorders (AWACs) and data from cameras from which wave runup is estimated. Furthermore, a sensitivity analysis has been performed to assess the impact of uncertainties in the beach bathymetry.

The first results show that under the RCP8.5 scenario, the expected coastline retreat under mean conditions would be of ~22 ± 5 meters at mid-century. Considering extreme waves conditions, the retreat would reach ~40 ± 5 meters.

It is worth mentioning that the three studied beaches have a very different exposure, granulometry and maritime climate, and in spite of that, the estimated uncertainty level is relatively low (~10-25%) in all of them. Therefore, the proposed methodologies along with their uncertainty analysis, might be extrapolated to any sandy beach with a reasonable high degree of accuracy. 

How to cite: Agulles, M. and Jordà, G.: Evaluating future beach reduction in a changing climate: Methodologies and uncertainties., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10094, https://doi.org/10.5194/egusphere-egu2020-10094, 2020.

D2754 |
Elise Vissenaekens and Katell Guizien

Ocean modelling has become an increasingly important tool to study population connectivity and is our only tool to anticipate changes in dispersal routes in future climates. To estimate the uncertainties in model predictions, a comparison was made between the simulated currents and in situ observations in the Gulf of Lion over the period of 2009-2013. The uncertainties in Eulerian current values were described using several statistical parameters, like the bias, the root mean square (RMSE), the naturalised root mean square (NRMSE), the Hannah and Heinold parameter (HH) and the correlation. Another parameter that was introduced was the correctness, which states the percentage of time the model was deemed “correct”, based on low HH values (<75%) and high correlation (>0.25). So far, the model simulated the flow speed correctly 60-70% of the time and the relative deviation between observed and simulated flow speed was about 10%. Furthermore, ensembles of Lagrangian tracks were simulated accounting for uncertainties in Eulerian flow speed. These uncertainties were either correlated to speed values or chosen according to their statistical distribution. The Lagrangian tracks were analysed to construct connectivity matrices with and without these Eulerian uncertainties. Resulting deviation in retention and larval transfer arising from flow speed uncertainty were quantified.

How to cite: Vissenaekens, E. and Guizien, K.: Quantifying connectivity uncertainty arising from circulation modelling inaccuracy., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2428, https://doi.org/10.5194/egusphere-egu2020-2428, 2020.

D2755 |
Hedi Kanarik, Laura Tuomi, Jan-Victor Björkqvist, Tuomas Kärnä, and Antti Westerlund

Currents in the Baltic Sea are relatively weak and are thus often expected to have a negligible effect on sea surface waves. To evaluate the magnitude of wave–current interactions in the Baltic Sea, we ran the third generation wave model WAM with and without surface currents from the 3D hydrodynamical model Nemo4. The results showed that the currents have a notable effect on wave field only on rare occasions and that the effects are largest in coastal areas of the Baltic Proper, most notably in the western Gotland Basin, and the Gulf of Finland. The simulations showed that the currents in the Baltic Sea can cause differences of significant wave height up to tens of centimeters. More notable effect was the change in the peak of the wave spectrum from swell to wind driven waves and vice versa in some occasions. In our study we mostly focus on the events of strong wave–current interactions in the northern Baltic Proper and Gulf of Finland as we have measured wave spectra available from these locations. From the comparison with wave buoy measurements we see that implementing surface currents slightly improves the modelled peak period in the Gulf of Finland. The Gulf of Finland is of special interest also because a group of ADCP’s were installed close to the wave buoy. The current measurements from these devices can therefore be used to evaluate the accuracy of the currents in the hydrodynamical model.

How to cite: Kanarik, H., Tuomi, L., Björkqvist, J.-V., Kärnä, T., and Westerlund, A.: The significance of wave–current interaction on modelled wave fields in the Baltic Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15900, https://doi.org/10.5194/egusphere-egu2020-15900, 2020.

D2756 |
María Liste Muñoz, Marc Mestres Ridge, Manuel Espino Infantes, Manel Grifoll Colls, Agustín Sanchez-Arcilla, Manuel García León, Marcos García Sotillo, and Enrique Álvarez Fanjul

Working in the coastal marine environment is highly challenging, among other reasons, due to the variety of extreme, seasonal, short and long-term environmental conditions that affect the coastline, beaches, infrastructures and port operations. The maritime climate directly affects the construction and maintenance of port infrastructures, the access of ships to ports, the safety of cargo handling operations, emergency response or the environmental management of effects of port operations. Currently, the ability to predict the sea state from a few hours to days has reached levels of precision and reliability unbelievable a few years ago. And all this, in combination with numerical measurements and predictions, has enabled significant advances in knowledge about meteorological and oceanographic conditions, making possible the development of forecasting systems to provide real, accurate and safe support in decision making in ports.

SAMOA initiative (System of Meteorological and Oceanographic Support for Port Authorities), developed by Spanish Port System (Puertos del Estado), in cooperation with Spanish Port Authorities, provides high-resolution coastal operational prediction systems in domains such as harbours and nearby coastal waters.

We present a high-resolution coastal operational prediction system which simulates the hydrodynamic in the Spanish Mediterranean Ports from April to September 2019. Bathymetry was built using a combination of bathymetric data from GEBCO (General Bathymetric Chart of the Oceans), and specific local high-resolution sources provided by port authorities. Daily updated hourly winds and heat and water fluxes from the Spanish Meteorological Agency forecast services were used as a surface forcing. The Regional Ocean Modelling System, ROMS, was used to investigate the hydrodynamics.

Three-day forecast of three-dimensional currents and other oceanographic variables, such as temperature, salinity, and sea level, were produced. These results were compared with field campaigns data, displaying agreements between model outputs and in-situ observations. Finally, a look ahead to the future of the operational prediction systems is provided as a useful tool to make informed decisions around port safety and efficiency.

We would like to acknowledge financial support from ECOSISTEMA-BC Project (CTM2017-84275-R), funded by the Spanish State Research Agency.

How to cite: Liste Muñoz, M., Mestres Ridge, M., Espino Infantes, M., Grifoll Colls, M., Sanchez-Arcilla, A., García León, M., García Sotillo, M., and Álvarez Fanjul, E.: Validation of the SAMOA Operational Forecasting System in Spanish Mediterranean Ports, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20429, https://doi.org/10.5194/egusphere-egu2020-20429, 2020.

D2757 |
Diego Bruciaferri, Marina Tonani, Huw W. Lewis, John Siddorn, Robert R. King, Pete Sykes, Juan M. Castillo, Andy Saulter, Niall McConnell, Isabella Ascione, and Enda O'Dea

Accurate modelling of the surface ocean dynamics is of paramount importance for many human activities such as search-and-rescue operations and offshore oil and wind power industry. During sea storm events, large waves can have a strong control on the surface ocean currents, making wave-current interaction a leading order process in the uppermost part of the ocean. North-west (NW) European shelf seas can be affected by extremely severe storms, increasing the need for precise predictions of the surface ocean dynamics.   

In this study we assess the impact of using a coupled ocean-wave modelling system to simulate the upper ocean dynamics of the NW European shelf during five storm events occurred in Winter 2016. Two versions of the eddy-resolving (1.5 km resolution) UK Met Office ocean-wave operational prediction system are compared: the first one uses the ocean and wave models in uncoupled mode; the second one is a coupled system including three ocean-wave interactions, namely the Stokes-Coriolis force, the modification of the surface stress by wave growth and dissipation and a wave height dependent ocean surface roughness. The assessment is carried out using the ocean currents and the Stokes’ drift reproduced by the two modelling systems to simulate the lagrangian trajectories of a number of iSphere (surface) and SVP (centered at 15m) drifters affected by the storms. The simulated trajectories are then compared with the observed drifters’ tracks. Some drifter trajectories representative of offshore, near the shelf-break and near the coast regimes have also been simulated switching on only one ocean-wave interaction per time, to better understand the relative impact of the three components we considered in the ocean-wave coupling.

Numerical results show that in the case of iSphere drifters, the trajectories simulated using ocean and wave-induced currents from the coupled system are much more accurate than the one obtained with the uncoupled system, especially near the shelf and the coasts, highlighting the importance of including wave feedback in the momentum equations of the ocean model.  For SVP drifters the effect of the ocean-wave coupling is less evident. This is probably due to the fact that the wave-current interactions considered in the current implementation of the coupled system mainly act in the proximity of the ocean surface, pointing out the need of including wave-induced effects able to influence also the sub-surface dynamics of the water column. However, results also seem to indicate that the reduced impact of the coupling might be related to some difficulties experienced by the ocean and wave models in properly representing some of the physical processes characterizing extreme storm events.

In conclusion, this study proves the importance of using a coupled ocean-wave system when simulating the ocean dynamics during storm events but also indicates where research efforts must be spent for improving the skills of the UK Met Office forecasting system.

How to cite: Bruciaferri, D., Tonani, M., Lewis, H. W., Siddorn, J., King, R. R., Sykes, P., Castillo, J. M., Saulter, A., McConnell, N., Ascione, I., and O'Dea, E.: Modelling the upper ocean dynamics of the north-west European shelf during storm events with the UK Met Office ocean-wave prediction system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4960, https://doi.org/10.5194/egusphere-egu2020-4960, 2020.

D2758 |
Ghada El Serafy and the EuroGOOS Coastal Working Group

The major interface between humans and the ocean occurs in the coastal seas. Marine industries thrive in this area while European citizens make daily use of the coastal ocean for tourism, leisure and recreation. Operational oceanography assists both industry and the general public to make decisions about their use of and access to the coastal ocean. The EuroGOOS community has developed, based on in-situ and satellite observations, data and modelling capacities, a wide range of products and services for such use cases. 
The EuroGOOS Coastal working group examines the entire value chain from coastal observations, satellite data, ocean forecasts and analysis, to products and services for coastal users. The working group reviews sustainability and fitness for purpose of the existing system and identifies gaps and future steps needed to secure and improve all elements of the coastal value chain. The EuroGOOS Coastal Working Group builds upon significant initiatives already completed or underway that have focused on coastal observatories. These include, but are not limited to, the work of EMODnet, SeaDataNet, CLMS, and CMEMS-In Situ Thematic Centres (INS TACs), which play significant role in making available key datasets for coastal areas, the JERICO-NEXT and JERICO-S3 EC projects, which work towards sustaining the JERICO-RI on long term, as well as activities within EuroGOOS working groups, platforms task teams, and the five regional operational oceanographic systems (ROOS). 
More specifically, the main activities of the EuroGOOS Coastal Working Group are: (i) mapping primary users of coastal products, (ii) reviewing available and potential coastal data sources with special focus on river discharges, (iii) preparing a comprehensive inventory of European operational models, (iv) reviewing coastal data assimilation frameworks for optimizing coastal sea monitoring and forecasting systems, (v) preparing an inventory of integrated coastal products and services, and (vi) formulating a EuroGOOS roadmap for the enhanced integration of coastal services into a EuroGOOS Coastal Working Group White Paper. 
The outcomes of the EuroGOOS Coastal Working Group activities are primarily designed to support four specific areas of the EuroGOOS Strategic Agenda 2020 and the short-term priority areas, namely (1) sustained fit for purpose observations, (2) data matters, (3) product development and (4) communication and outreach. On the other hand, in broader sense these activities contribute to the coastal community through peer reviewed articles such as the review of operational modelling capacity in European Seas (Capet et al., submitted) and by promoting collaboration to initiate new opportunities to effectively serve the coastal users in the industry (e.g. aquaculture sector) as in the H2020 FORCOAST project (www.forcoast.eu). 

How to cite: El Serafy, G. and the EuroGOOS Coastal Working Group: Aim, activities and early outcomes of the Coastal Working Group of the European Global Ocean Observing System (EuroGOOS), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22401, https://doi.org/10.5194/egusphere-egu2020-22401, 2020.

D2759 |
Manel Grifoll, Gorka Solana, and Manuel Espino

This contribution analyze “in-situ” data obtained in the unexplored estuary of Inhambane Bay (Mozambique). Inhambane Bay is a bar-built estuary with a length of 30.5 km and an extension of 288 km2. Synchronous measurements of sea-level, temperature/salinity and water current velocity were obtained during two intensive field campaigns covering dry and wet climatological seasons. Additional Sea Surface Temperature (SST) obtained from GHRSST project were used to charcterize the estuary. The first results reveal a meso-tidal estuary with water currents of 1.0 m/s. The water velocity profiles show an homogeneous profile in the ADCP measurements. The hydrographic surveys and GHRSST product confirms a remarkable seasonal variability. The largest SST are observed from November to May, coinciding with the warm and rainy season. Salinity profiles are almost vertical and the variability follows the direction of the tidal phase (lower salinity values are observed during low tide). In consequence, the estuary is well-mixed with salinity increasing values downward the estuary. The flushing time is estimated between 1 -3 days in function of the neap/spring tide using the Tidal Prism method.


 ECOSISTEMA project (CTM2017-84275-R)

How to cite: Grifoll, M., Solana, G., and Espino, M.: Hydrodynamic characterization of a meso-tidal estuary: Inhambane Bay (Mozambique), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6090, https://doi.org/10.5194/egusphere-egu2020-6090, 2020.

D2760 |
Martin Vodopivec and Matjaž Ličer

When modelling coastal areas in high spatial resolution, it is also essential to obtain atmospheric forcing with suitably fine grid. The complex coastline and coastal orography exert strong influence on atmospheric fields, wind in particular, and the east Adriatic coast with numerous islands and coastal mountain ridges is a fine example. We decided to use a high resolution COSMO atmospheric reanalysis for our long term ROMS_AGRIF hindcasts, but in our initial experiments we found out that the atmospheric model significantly underestimates the short wave flux over the Mediterranean Sea, probably due to overestimation of high clouds formation and erroneous sea surface temperature used as a boundary condition. We explore different atmospheric models and different combinations of fluxes - direct, diffuse and clear sky solar radiation and combinations of fluxes from different atmospheric models (eg. ERA5). We compare them with solar irradiance observations at a coastal meteorological station and run year-long simulations to compare model sea surface temperature (SST) with satellite observations obtained from Coprenicus Marine Environment Monitoring Service.

How to cite: Vodopivec, M. and Ličer, M.: Optimizing COSMO_REA6 reanalysis radiation flux for a high resolution coastal ocean model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3305, https://doi.org/10.5194/egusphere-egu2020-3305, 2020.

D2761 |
| Highlight
Malgorzata Stramska, Joanna Stoń-Egiert, Miroslawa Ostrowska, and Jaromir Jakacki

Potential influences of various environmental factors on phytoplankton growth rates in the Baltic Sea are discussed. Our focus is on quantitative comparisons of growth rates of two phytoplankton functional types, diatoms and cyanobacteria. Growth rates are calculated as a function of quanta absorbed by phytoplankton. This in turn depends on phytoplankton exposition to light, which was simulated to represent realistic conditions encountered in the Baltic Sea in summer. In addition, phytoplankton absorption capability was characterized by absorption coefficients derived from measurements on phytoplankton mono-cultures isolated from the Baltic Sea. Estimated exposition of phytoplankton to photosynthetically available radiation (PAR) in surface waters can change about five times in case of the same solar surface insolation and water turbidity, solely due to changes in the mixed layer depth from 2 to 20 meters. When additionally changes in water turbidity are considered, phytoplankton PAR exposition can change by one order of magnitude. Light exposition and absorption properties of phytoplankton determine the effectiveness of light absorption. In our simulations for the same species of phytoplankton, changes in light exposition resulted in differences of an order of magnitude of absorbed quanta. The importance of accounting for absorptive properties is underlined through comparisons of the number of quanta absorbed by different phytoplankton types in the same environmental conditions. The effectiveness of light absorption translates to different growth rates achieved by each phytoplankton type. Our results support the notion that knowledge about phytoplankton absorption properties and light exposition is crucial when modeling phytoplankton in the Baltic Sea. Further progress is currently hindered by a lack of systematic information about maximum phytoplankton growth rates and their responses to specific environmental conditions for different functional types. Such information should be inferred in the future in specially designed laboratory experiments, that encompass realistic ranges of phytoplankton exposition to light, nutrients, temperatures and other conditions.

This work has been funded by the National Science Centre (contract number: 2017/25/B/ST10/00159 entitled: “Numerical simulations of biological-physical interactions and phytoplankton cycles in the Baltic Sea”) and by the statutory funds of IOPAN.

How to cite: Stramska, M., Stoń-Egiert, J., Ostrowska, M., and Jakacki, J.: Modeling the growth rates of cyanobacteria and diatoms in the Baltic Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3372, https://doi.org/10.5194/egusphere-egu2020-3372, 2020.

D2762 |
Yong-Jun Lin, Chih-Chung Wen, Kai-Yuan Ke, and Yih-Chi Tan

In 2017, dead pigs infected with African swine fever were found on the beach of Tianpu, Kinmen, an offshore island of Taiwan. After the event, the Kinmen government carried out a thorough pig farm quarantine. However, none infected pig was found in any of the pig farms. This study aims to identify where the dead infected pig came from. Affected by ocean currents, marine drifts can often reach hundreds or thousands of kilometers away from their origins. During the winter, ocean currents across the north of the Taiwan Strait from west to east may transport the pigs from the coast of Fujian and Zhejiang, China, to the coast of north-central Taiwan. Another possible driven force is the near-shore current of western China. In order to analyze the possible drifting path of pigs, the hydrodynamic model and the particle tracking model were applied. Pigs were simulated as mass particles. The simulation domain includes sea area nearby Kinmen and China where pigs may originate. Considering the effect of the currents and wind from 2018/12/26 to 2019/1/3, three possible drift scenarios were set for analysis, including (S1): originated from Weitou Bay; (S2): originated from Jiulong River estuary; (S3) originated from the coast of Quanzhou. The results showed that the most possible scenario is S3.

How to cite: Lin, Y.-J., Wen, C.-C., Ke, K.-Y., and Tan, Y.-C.: The Simulation of Drifting Dead Pigs in the Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3883, https://doi.org/10.5194/egusphere-egu2020-3883, 2020.

D2763 |
Nikos Flokos and Maria Tsakiri

corresponding author: N.Flokos



Sea level change is one of the key indicators of climate change with numerous effects such as flooding, erosion of beaches, salt intrusion.  The detailed global picture of sea level and the monitoring of its spatial-temporal changes is performed by Satellite Altimetry (SA). Nowadays, SA data compare well with measurements from the global tide gauge network, but the aim of 0.3 mm/year accuracy in the altimeter derived rate of global mean sea level rise is still not fully met. 

Whilst the precise determination of global and regional sea level rise from SA data is promising, there is however an observational gap in our knowledge regarding the coastal zone. While Tide Gauges (TG) are usually located at the coast, therefore providing coastal sea level measurements, altimeters have difficulties there. Filling this gap becomes important when considering that the impact of sea level rise can be devastating on the coast with effects on society and ecosystems. This makes it even more significant knowing that there are many stretches of the world’s coast that still do not possess in situ level measuring devices.  

This work aims to discuss the available data and methods that link the SA measurements of sea level rise with TG measurements. Whilst there is rich literature on relevant applications, it is important to have a clear and concise methodology on this.

Tide gauge data

Several post processing steps need to be applied to the raw TG data to enrich the raw Sea Surface Heights (SSH) values and make them comparable with SA data. There are several geophysical corrections, such as pressure and wind effects, which can be applied to TG data in order to deduce  Sea Level (SL) and be consistent with altimeter data. High frequency atmospheric effects on TG data are corrected using the Dynamic Atmospheric Correction (DAC) provided by AVISO. One other large uncertainty is the vertical stability of the TG benchmark over time. TG data must be corrected for the Vertical Land Motion (VLM) to enable the comparison of two sea level measurements (TG and SA) and their later integration within the surfaces of the absolute sea heights. The main VLM dataset can be obtained from SONEL database (SONEL 2016) which provides crustal velocities from the continuous GNSS measurements at sites collocated to the TG.

Satellite altimetry data

Whilst Satellite Altimetry over the open ocean is a mature discipline, global altimetry data collected over the coastal ocean remain still largely unexploited. This is because of intrinsic difficulties in the corrections and issues of land contamination in the footprint that have so far resulted in systematic flagging and rejection of these data. In this work, the relevant methodology to overcome these problems and extend the capabilities of current and future altimeters to the coastal zone (coastal altimetry) will be discussed and a number of coastal altimetry data sets will be used (eg SARvatore, X-TRACK, RADS etc). Finally, a practical example using real data sets over the Aegean Sea will be presented. 



How to cite: Flokos, N. and Tsakiri, M.: Observing Sea Level Changes Using Satellite Altimetry and In Situ Data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5817, https://doi.org/10.5194/egusphere-egu2020-5817, 2020.

D2764 |
Eunkyung Lee, Jeong-Eon Moon, Young-Je Park, and Tai-Hyun Han

Red tide, which occurs off the southern coast of the Korean Peninsula, is a maritime phenomenon that usually occurs between June and September every year, mostly by Cochlodinium polykrikoides single species. There are very few studies using the analytical methods of the inherent and apparent optical properties for these red tide. Ahn et al.(2009) analyzed the inherent optical properties of 26 species of red tide organisms occurring off the southern coast of the Korean Peninsula. Kim et al.(2016) distinguished the optical characteristics for Cochlodinium polykrikoides using field data and Hydrolight simulator. Using these analytical methods, we will understand the ocean optical properties of red tide and use the remote sensing reflectance simulator in the future to produce the input data necessary for developing the red tide analysis technology based on machine learning. Therefore, in this study, as an initial analysis, we will compare the in-situ data of red tide and non-red tide waters off the southern coast of the Korean Peninsula in September 2014 and August 2017 to identify differences in the spectral form and compare the ability of the remote sensing reflectance spectrum with the field data using a remote sensing reflectance simulator.

How to cite: Lee, E., Moon, J.-E., Park, Y.-J., and Han, T.-H.: Comparison of optical characteristics in non-red tide and red tide areas in the South Sea of Korea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6605, https://doi.org/10.5194/egusphere-egu2020-6605, 2020.

D2765 |
Matjaz Licer, Lojze Žust, and Matej Kristan

Storm surges are among the most serious threats to Venice, Chioggia, Piran and other historic coastal towns in Northern Adriatic. Adriatic Sea has a well defined lowest seiche period of approximately 22 hours and its amplitude decays on the scale of several days, reinforcing (or diminishing) the tidal signal, depending on the relative phase lag between tides and surges. This makes prediction of Adriatic sea level extremely difficult using conventional deterministic models. The current state-of-the-art predictions of sea surface height (SSH) hence involve numerical ocean models using ensemble forcing. These simulations are computationally-demanding and time consuming, making the method unsuitable for operational or civil rescue services with limited access to dedicated high-performance computing facilities.

Ensemble approach to deep learning offers a possible solution to the challenges described above. Even though training a deep network may involve substantial computational resources, the subsequent forecasting -- even ensemble forecasting -- is fast and delivers near-realtime SSH predictions (and associated error variances) on a personal computer. In this work we present an ensemble SSH forecast using new deep convolutional neural network for sea-level prediction in the Adriatic basin and compare it to the standard approach using state-of-the-art publicly available modelling components (NEMO ocean circulation model and TensorFlow libraries for deep learning).

How to cite: Licer, M., Žust, L., and Kristan, M.: Ensemble Approach to Deep Learning and Numerical Ocean Modelling of Adriatic Storm Surges, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6658, https://doi.org/10.5194/egusphere-egu2020-6658, 2020.

D2766 |
Shih-Feng Su and Wen-Kai Weng

Most coral reef islands in the South China Sea are primary influenced by monsoons from the northeast in winter to the southwest in summer. Because the length scale of the islands ranges between O(100 m) and O(1000 m), nearshore waves and currents on the windward and leeward sides are modulated by seasonal wave directions as well as reef morphology. It is well known that long-period swell and infragravity waves play a vital role in dominating hydrodynamics and sediment dynamics on fringing reefs. However, spatial characteristics of long waves on the entire islands have not been well studied. In the present study, a phase-resolving Boussinesq-type wave model, is employed to investigate wave distributions around Taiping Island in the South China Sea during the monsoon. Wave transformations of refraction, diffraction, reflection and nonlinear wave interactions on the complex reef geometry are simulated using a high resolution grid. Model results will display spatial variability of significant wave height, infragravity waves and nearshore currents around the reef platform. The importance of long wave diffraction and resulting wave frequency components at the leeward side of the island will be examined. A small harbor located at the southern island often experiences harbor oscillations during the winter monsoon, even it located at the leeward side. Harbor oscillations forced by periods of wind-wave, swell and infragravity waves will be explored to provide critical indicators for the harbor management.

How to cite: Su, S.-F. and Weng, W.-K.: Spatial variations of long-period waves and harbor oscillations around Taiping Island in the South China Sea , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7364, https://doi.org/10.5194/egusphere-egu2020-7364, 2020.

D2767 |
Di Tian

Impacts of climate change on heat budget in the Eastern China Seas (ECSs) are estimated under the historical, RCP4.5 and RCP8.5 scenarios using an atmosphere-ocean coupled regional climate model system (REMO/MPIOM). Solar radiation contributes the largest heat source of the ECSs. The heat gain achieved by solar radiation is overruled by thermal radiation, latent heat flux and sensible heat flux released at the ocean surface. The air-sea heat exchange thus cools the ECSs, whereas an overall warming is found for the ECSs. An increased oceanic heat transport by ocean currents balances this reduced heat supply by the sea surface heat fluxes. In particular, the water transport through Taiwan Strait brings the largest amount of heat into the ECSs. Despite of an inward heat transport onto the ECS shelf caused by the Kuroshio intrusion occurring northeast of Taiwan, overall, the shelf break section acts as a heat sink for the ECSs. The net heat gain/loss by the Tsushima Strait is marginal. Under the climate projection scenarios, the net heat loss from the shelf break section reduces, probably associated with the change in surface wind. Thus the net heat transported into the ECSs through the lateral boundaries increases slightly under these scenarios, leading to an overall warming of the ECSs, relative to 20C run. Noteworthy, the warmer SST, along with strengthened wind, further enhances the surface evaporation, providing a negative feedback onto the net effect of oceanic transport.

How to cite: Tian, D.: The modeling responses of heat budget in the Eastern China Seas to global warming, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8649, https://doi.org/10.5194/egusphere-egu2020-8649, 2020.

D2768 |
Marco Bajo, Iva Međugorac, Georg Umgiesser, and Mirko Orlić

This work assesses the impact of assimilating the sea level data, with an Ensemble Kalman Filter, on storm surge and seiche modelling. The study area is the Adriatic Sea, where seiches are always present after a storm surge, and often overlap on a new storm surge with a possible amplification of the total sea level. Due to errors in the wind and pressure forcing, the forecast of such extreme events is rather challenging in the Adriatic Sea, and a wrong reproduction of such pre-existing seiches reflects on a bad sea-level forecast. Here we show, by two case studies, that the assimilation of sea-level data along the coasts of the Adriatic basin is able to correct the initial state of the hydrodynamic model. Since the initial state is particularly important in the case of pre-existing seiches, the reduction of the initial error propagates several days into the forecast. The two cases here presented were between the most extreme storm surge events in the last years and they both included the pre-existing seiches. The initial forecast was very poor, due to the fact that the wind was underestimated. The assimilation of 3-day long hourly sea level data at eleven stations distributed along the Adriatic coasts produces a better forecast in both cases. Moreover, the ensemble spread allows the uncertainty of the forecast to be estimated, even if the estimate should be calibrated over time in order to be more reliable.

How to cite: Bajo, M., Međugorac, I., Umgiesser, G., and Orlić, M.: Impact of sea level data assimilation on the storm surge and seiche forecasts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8902, https://doi.org/10.5194/egusphere-egu2020-8902, 2020.

D2769 |
| Highlight
Subhadeep Rakshit, Andrew Cogswell, Sebastian Haas, Emmanuel Devred, Richard Davis, Kate Patterson, Douglas Wallace, and Christopher Algar

Lack of bottom water exchange in fjord-like estuaries can result in low oxygen conditions and creating sites of redox-sensitive biogeochemical processes, such as denitrification. In many of these systems, occasional intrusions of well-oxygenated bottom water may temporarily alter redox gradients and sediment-water biogeochemistry. Quantifying the magnitude and importance of these changes is a challenge due to the short timescales over which these events can occur. Here we present results from Bedford Basin, a 71 m deep coastal fjord in eastern Canada, where a 20-year, weekly timeseries of bottom water conditions indicates that autumn wind-driven intrusion events are a common, but infrequent, feature of its circulation. To examine the impact of these intrusions on biogeochemistry, we deployed a benthic instrument pod at 60 m depth to record high-resolution measurements of temperature, salinity, nitrate, oxygen, and fluorescence over a 4-month period during the fall of 2018.  During this time we captured two intrusion events, one in mid-Oct and another in mid-Nov. Both intrusion events occurred on a timescale of hours and resulted in sharp changes in temperature, salinity, oxygen, and nitrate.  We used these measurements to constrain a coupled sediment-water column reactive transport model to examine the immediate and annual impacts of these intrusion events on oxygen and nitrogen dynamics in the basin bottom waters and across the sediment-water interface.

How to cite: Rakshit, S., Cogswell, A., Haas, S., Devred, E., Davis, R., Patterson, K., Wallace, D., and Algar, C.: The influence of bottom water intrusion events on the biogeochemistry of a coastal fjord, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9525, https://doi.org/10.5194/egusphere-egu2020-9525, 2020.

D2770 |
Duy-Toan Dao, Hwa Chien, and Pierre Flament

A 16 Rx element linear array HF radar system (LERA III), working at 27.75 MHz and 300kHz in bandwidth, was installed at the north of Taichung harbor at the western coast of Taiwan in November 2018. This LERA system is low-cost, compact in size, easy to set-up, and maintain. The purpose of present studies is to implement algorithms for retrieving wave and wind fields and assess the system performance in terms of operational mode. For inter-comparison, the long-term in-situ wave data measured by an AWAC was adopted. Wind data were measured from a coastal wind gauge. The inter-comparisons between radar data and in-situ data were carried out on seasonal basis, including severe sea states during winter monsoon and passage of typhoon as well as calm seas during spring.

For the data processing, the Doppler-range spectrum for each azimuth direction was extracted by using the classical beam-forming technique and then provided as level 1 product for further analysis. Regarding the method for retrieving wave parameters, formulations directly derived from Barrick’s assumption was implemented. In those formulas, wave parameters are calculated based on the ratio of the 2nd order component multiplied by the coupling coefficient function to the 1st order component in the Doppler spectrum. It means that no empirical constants were included. Initially, Wyatt’s (1999, 2011) and Walsh & Howell’s (1993) methods were applied to determine the lower and higher bounds that separate the 1st and 2nd order component. For wind speed inversion, Dexter & Theodorides’s (1982) method was adopted. The Bragg wave direction was used as a proxy to the direction of the wind field.

It is found that when using Wyatt’s (1999, 2011) method, the wave height and period results often lead to bias estimations for severe sea-state, and with the presence of highly variable surface current. In order to improve the accuracy, adaptive methods for the identification of spectra component areas is crucial. In this study, an alternative method is proposed. This method is developed based on the concept proposed by Kirincich (2017), which includes the pretreatment of Doppler-rang spectrums, marker-controlled watershed segmentation, and an image processing technique. In this research, we will demonstrate the advantages of using the new method for wave and wind field retrieval. From comparative studies, the error indexes based on the sea truth data are discussed. It is found that the accuracy would be improved using the proposed method, especially for the cases of varying current fields, severe sea state, and noisy radio background.

Key words: high-frequency surface wave radar; phased array antennas; significant wave height, wave period, marker-controlled watershed segmentation (MCWS) techniques.

How to cite: Dao, D.-T., Chien, H., and Flament, P.: Improving the uncertainty of ocean surface wind and wave parameters estimated by a single HF radar system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12210, https://doi.org/10.5194/egusphere-egu2020-12210, 2020.

D2771 |
Daosheng Wang, Haidong Pan, and Lin Mu

The seasonal variability of the M2 tide exerts a major influence on the coastal ocean environment. In this study, a novel method, namely modified enhanced harmonic analysis (MEHA), is developed to synchronously extract the temporally varying amplitudes and phase lags of significant tides and the constant values of the other constituents. The seasonal variability of the M2 tide in the Bohai Bay, China, is investigated by analyzing one-year sea level observations at two stations with MEHA.

In ideal twin experiments, the artificial sea level observations were analyzed. Both the estimated temporally varying amplitude and phase lag of the M2 tide and constant values of the S2, K1 and O1 tides using MEHA were much closer to the prescribed values than those obtained using the other methods, indicating the capability and efficacy of MEHA. When the real sea level observations were analyzed using MEHA, the estimated M2 tidal amplitude has significant seasonal variability, with large values in summer and small values in winter, which is robust and not affected by experimental settings. The results of numerical experiments indicate that the seasonality of vertical eddy viscosity induces seasonal variations of the M2 tide in the Bohai Bay.

How to cite: Wang, D., Pan, H., and Mu, L.: Seasonal variability of the M2 tide in the Bohai Bay: development and application of modified enhanced harmonic analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12217, https://doi.org/10.5194/egusphere-egu2020-12217, 2020.

D2772 |
Anna Przyborska, Maciej Muzyka, Jan Andrzejewski, Jaromir Jakacki, and Daniel Rak

Offshore Wind Farms play a significant role in ensuring Europe's energy security. In Poland, a significant increase in the  number  of  newly-constructed  wind turbines  has  been  observed  in  recent  years. Wind power is "clean", but not completely free of environmental impacts. Their impact on the environment is difficult to assess. The impact of dredging works on suspended matter created during construction works will be presented  based on numerical model results. A model has been built based on MIKE, tools supplied by the Danish Hydraulic Institute (DHI) and the Weather Research and Forecasting model (WRF)- mesoscale numerical weather prediction system. Based on the numerical model created, analysis of the temporal and spatial variability of the spreading suspension generated from dredging works carried out during construction works aimed at positioning the wind turbines in appropriate places.

The advective-diffusive character of transported matter is the most natural clean, their direction, turbulent viscosity and sedimentation rate. Authors evaluated that during the construction phase, concentration of the suspended sediment will exceed 10 mg/l, which is denerous value for cod larvae, for short time (no longer than 48 hours) and will cover small area. The deposition will be irrelevant, the largest rate will occur in the immediate vicinity of the construction works and it will decrease with the distance. The range of the transferable suspension will not exceed 15 km. Cumulative factors significantly increase the concentration of the suspension (in a critical case they may even double it). They may occur when simultaneous actions are taken to prepare the foundation for more than one wind turbine at the same time, which is rather technical impossible because there is not a lot of special purpose sea vessel that are able to work on construction of basements of the offshore wind generators.


How to cite: Przyborska, A., Muzyka, M., Andrzejewski, J., Jakacki, J., and Rak, D.: The spreading of suspended matter formed during construction works of offshore wind farms, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13845, https://doi.org/10.5194/egusphere-egu2020-13845, 2020.

D2773 |
Jan Andrzejewski, Jaromir Jakacki, Maciej Muzyka, and Anna Przyborska

The Baltic Sea is inland, Shelf Sea in northern part of Europe. It is shallow with average depth of 52 meters and deepest point 459 meters located at Landsort Deep. Baltic Sea is connected with North Sea via the Danish Straits (comprising of Great Belt, Little Belt and Øresund). These systems ensure only limited exchange between oceanic waters and seawaters, which affect the low salinity in Baltic reservoir. Runoff from surrounding lands (approximately 200 rivers) and positive difference of precipitation minus evaporation additionally refreshes water and makes Baltic a brackish sea. The only charge of salt comes from the North Sea with so-called inflows or less frequent occurring Major Baltic Inflows (MBI). This exchange between Danish Straits is the key for properly working simulation. In this work the tool, well known as NEMO, was used to perform the numerical simulation for the Baltic Sea area. This presentation is focused on the first stage of validation of the model results for the Baltic Sea region where influence of open boundary conditions is noticeable as soon as possible. The main change in the model is the assimilation of sea surface height in Kattegat area. Also water outflow mass controlling from the Baltic Sea has been introduced. The properly working open boundary conditions affect the water exchange between Baltic Sea and North Sea, thus the MBI and minor salty inflows are well represented. This is very important part in modeling the Baltic
Sea, where narrow Danish Straits limits the water exchange which controls the salt budget, adding the salt with inflows and receiving brackish outflow out to the Ocean. This work presents comparison between model output with results measured in situ and from other validated model, the period which is compared is the Major Baltic Inflow in the beginning of 1993.

How to cite: Andrzejewski, J., Jakacki, J., Muzyka, M., and Przyborska, A.: Setting up the NEMO (Nucleus for European Modeling of the Ocean) for Baltic Sea region - open boundary conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15045, https://doi.org/10.5194/egusphere-egu2020-15045, 2020.

D2774 |
| Highlight
Irina Dinu, Vicente Gràcia, Manuel García-León, and Adrian Stanica

The Danube Delta coast is part of the Danube Delta Biosphere Reserve, thus being aimed to preserve its typical natural habitats. Over the last decades, human interventions along the Danube River, as well as coastal navigation and harbour protection works on the Romanian coast have determined the reduction of sediment supply along the Danube Delta coast, which is nowadays affected by erosion on its widest part.

Sustainable management plans for the Danube Delta coast include the use of working-with-nature solutions.

In this work, the effect of artificial reefs on the wave heights along the Danube Delta coast is studied. The results of a previous wave climate study and a wave model have been used for this purpose. Simulations have been performed for different setup of artificial reefs and for extreme storms with various return periods. The effect of sea level rise has also been taken into account.

Our results show that artificial reefs are significantly effective in reducing the wave heights along the Danube Delta coast. However, further detailed analysis concerning the impact of such a coastal protection solution is still needed.  

How to cite: Dinu, I., Gràcia, V., García-León, M., and Stanica, A.: Are artificial reefs an appropriate solution to protect the Danube Delta coast?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-246, https://doi.org/10.5194/egusphere-egu2020-246, 2020.

D2775 |
Sandra-Esther Brunnabend, Lars Axell, Maximo Garcia-Jove, and Lars Arneborg

The Orust fjord system, located on the west coast of Sweden, has openings on both ends and consists of several fjords that are connected by narrow and shallow channels. The fjord system includes the islands Orust and Tjörn as well as various smaller islands. The water exchange between the Kattegat and the different fjords is influenced by different factors, such as winds, tides, and density gradients. However, advection between the open sea and the complex fjord system are not yet well understood as lower resolution ocean models cannot resolve the small scale structures of the fjords and their connections. In addition, observations are rather sparse.

Therefore, the water exchange in the Orust fjord system is simulated using a high resolution (50 meter) NEMO3.6 ocean model setup, forced with the UERRA atmospheric reanalysis dataset. The lateral open boundary conditions for temperature, salinity, sea levels and velocities are provided by a low resolution (1.85 km) NEMO3.6 simulation, which spans the Baltic Sea and North Sea regions.

The model results are validated by comparison of modelled temperature, salinity, velocities and sea surface height with in-situ measurements. A detailed analysis of the different drivers of modelled water exchange between the Kattegat and the fjord system as well as between the different basins is presented. In general, the modelled water properties of the near surface layer in the fjord system are influenced by the Skagerrak surface water, which is controlled by the prevailing northward flowing Baltic Sea water. However, the residence times of water masses below the sill level are longer than the ones of the surface water masses as dense inflows of Skagerrak water in the basins create a strong stratification leading to weak vertical exchange.

How to cite: Brunnabend, S.-E., Axell, L., Garcia-Jove, M., and Arneborg, L.: Drivers of water exchange in the ORUST fjord system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2338, https://doi.org/10.5194/egusphere-egu2020-2338, 2020.

D2776 |
Yvan Gouzènes, Fabien Léger, Anny Cazenave, Florence Birol, Marcello Passaro, Fernando Nino, Christian Schwatke, Jean-François Legeais, and Jérome Benveniste

We present results of contemporary coastal sea level changes along the coasts of different
regions of Southeast Asia derived from a dedicated reprocessing of satellite altimetry data.
This work is performed in the context of the ESA ‘Climate Change Initiative’ sea level project
dedicated to provide altimetry-based sea level time series in the world coastal zones. Here is
focus on Southeast Asian Seas. High-frequency (20 Hz) sea level data from the Jason-1,
Jason-2 and Jason-3 missions are considered. The data are first retracked using the ALES
adaptive leading edge subwaveform retracker and further combined with the X-TRACK
processing system developed to optimize the accuracy of the sea level time series in coastal
oceans. Rates of sea level change are estimated over the period 2002-present along the Jasontracks,
from the open ocean to the coast. Different coastal sea level trend behaviors are
observed over the study period: constant trends from open ocean to the coast, sometimes
decreasing trends, or increasing trends within the last few km to the coast. We compare the
computed coastal trends in Southeast Asia with results we previously obtained in other
regions (Mediterranean Sea, Western Africa, Northeastern Europe). We further discuss the
various small-scale processes able to explain departure of the coastal sea level rate from the
offshore (open ocean) rate.

How to cite: Gouzènes, Y., Léger, F., Cazenave, A., Birol, F., Passaro, M., Nino, F., Schwatke, C., Legeais, J.-F., and Benveniste, J.: Observed coastal sea level changes in Southeast Asia from retracked altimetry over 2002-present, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3572, https://doi.org/10.5194/egusphere-egu2020-3572, 2020.

D2777 |
| Highlight
Ai-Jun Pan, Fang-fang Kuang, Kai Li, and Xu Dong

A field survey revealed a rare realization of upwelling event in the northwestern Hainan Island (UNWHI) on July 24, 2015. Model experiments suggest that the UNWHI is not locally generated, but can be treated as northward extension of the upwelling southwest off Hainan Island (USWHI) under favorable wind conditions. Therefore, presence of the USWHI is vital for the UNWHI occurrence. Tidal mixing is testified to be the primary driving force for the USWHI, whilst southerly winds plays an essential role in the induction of the UNWHI. Moreover, it is demonstrated that the UNWHI is not a stable, but intermittent coastal upwelling system. Shallow basin of the Beibu Gulf makes the interior circulation vulnerable to local monsoon changes. Given the favorable southerly winds, a cyclonic gyre northwest off Hainan Island will be induced and which, leads to northward coastal current and consequently, the UNWHI is to be formed due to the northward transport of the USWHI. Conversely, the UNWHI vanishes during northerly winds period, because the basin-scale anticyclonic gyre results in a southward current west off the Hainan Island and which, acts to push the upwelled water of the USWHI offshore and away from the northwestern Hainan Island. In addition, our diagnostics indicates that contributions from surface heat fluxes to the UNWHI occurrence is negligible. Besides, it also reminds us that application of a high-frequency, much closer to reality wind field is necessary for the coastal upwelling simulation. 

How to cite: Pan, A.-J., Kuang, F., Li, K., and Dong, X.: A Rarely Witnessed Summertime Upwelling Event northwest off the Hainan Island, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6287, https://doi.org/10.5194/egusphere-egu2020-6287, 2020.

D2778 |
Junpeng Zhang, Aijun Pan, Fangfang Kuang, Chunsheng Jing, Muh Hasanudin, Edi Kusmanto, and Deny Sutisna

A three-dimensional baroclinic nonlinear numerical model is employed to investigate the seasonal evolution features of water transport in the Lembeh Strait of north Sulawesi. In general, the direction of water flow in the strait is oriented northward with a maximum volume of about 4x10-3Sv in August. Interestingly, the volume transport will decrease to nearly zero from November to January. Water transport is mainly controlled by seasonally changed monsoon forcing. The large-scale ocean circulation nearby North Sulawesi is weaker during November-January and stronger from July to September. In addition, the source of water bypasses the Lembeh Strait in different seasons is diagnosed and testified by tracer-release experiments. It suggests that most of the water through the narrow channel is emanated from the southern off the Strait, not only the surface water, but also the deep water brought by the upwelling and the internal tides.

How to cite: Zhang, J., Pan, A., Kuang, F., Jing, C., Hasanudin, M., Kusmanto, E., and Sutisna, D.: Seasonal Evolution Features of Water Transport in the Lembeh strait of North Sulawesi, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6353, https://doi.org/10.5194/egusphere-egu2020-6353, 2020.

D2779 |
Huib E. de Swart and Inge van Tongeren

Many estuarine systems experience increased salt intrusion, which is harmful for ecology and agriculture and may cause problems for fresh water supply to cities. Some causes of salt intrusion are extraction of fresh water in the upper reaches of the estuary and climate change. Besides, anthropogenic measures, like deepening of channels, are known to have a strong impact on the salt balance.

This contribution focuses on salt intrusion in estuarine networks, which consist of multiple connected channels. The motivation of the study arose from observations in the Yangtze estuary that reveal frequent overspill of salt between its different channels. To understand the underlying physics of such behaviour, an exploratory, width- and tidally averaged model has been developed and analysed. This model describes the competition between export of salt by river flow and import of salt by density-driven flow and horizontal diffusion. Its key new aspect is that it generalises an earlier model MacCready (2004) from a single channel to estuarine networks. The new model calculates the distribution of salt in, and salt exchange between the channels, as well as the distribution of river water over the different channels.  

Here, results will be presented for a simplified estuarine network consisting of the South Channel, South Passage and North Passage of the Yangtze Estuary. It will be shown that, for the present-day situation, dry season and spring tide, salt intrusion is larger in the South Passage than in the North Passage. As will be explained, this is mainly due to the different geometry of the two channels. Furthermore, it will be shown that there is slightly more river water transport through the South Passage than through the North Passage, except during high river discharge and neap tide. These results agree with field data and results from numerical studies.

Other results that will be presented are the sensitivity of salinity intrusion length and distribution of river water over the different channels to changes in, respectively, upstream river discharge, tidal currents and human interventions. Specifically, the effects of the creation of a Deepwater Navigation Channel in the North Passage on salt dynamics will be shown and discussed.

MacCready, P. 2004. Toward a unified theory of tidally-averaged estuarine salinity structure. Estuaries 27, 561-570.

How to cite: de Swart, H. E. and van Tongeren, I.: Salt intrusion in an estuarine network, a study with an exploratory model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8535, https://doi.org/10.5194/egusphere-egu2020-8535, 2020.

D2780 |
Laura Tuomi, Aarno Kotilainen, Hedi Kanarik, Joonas Virtasalo, Olga Vähä-Piikkiö, and Heidi Pettersson

Sea floor erosion can be induced by waves, bottom currents and ice. Although the Gulf of Bothnia in the Baltic Sea is a relatively small basin, the record value of significant wave height is 8.1 m with highest individual wave of 15 m. In the present climate the seasonal ice cover limits the wave growth during winter time, but in the future climate it is estimated that ice extent will reduce which can lead to more severe wave climate. Thus, the effect of waves on the bottom sediment erosion is expected to increase. We used wave model WAVEWATCH III to do a 30-year high-resolution hindcast for the Gulf of Bothnia. The hindcast wave parameters were validated against wave buoy and altimeter wave measurements to ensure good quality of the wave hindcast. The hindcast near-bottom orbital velocities and amplitudes were used to estimate wave-induced bottom shear stress. These calculations are based on the wave spectra, taking into account the effect of different wave heights and wave lengths. The results were used to evaluate the extent of areas that experience significant wave-induced bottom stress under the present climate. Furthermore, the results show how often and for how long periods the wave-induced stress exceeds the critical values for sediment resuspension to take place. The estimates of the critical values for resuspension are calculated utilising the seabed sediment data available for the Gulf of Bothnia. The adequacy of the results is evaluated by comparing the known erosional seafloor areas to the ones estmated based on the hindcast values. This study is part of the SmartSea project of the Strategic Research Council of the Academy of Finland (grant no. 292 985).

How to cite: Tuomi, L., Kotilainen, A., Kanarik, H., Virtasalo, J., Vähä-Piikkiö, O., and Pettersson, H.: Estimating wave-induced bottom shear stresses in the Gulf of Bothnia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11158, https://doi.org/10.5194/egusphere-egu2020-11158, 2020.

D2781 |
Elina Miettunen, Laura Tuomi, and Kai Myrberg

The Archipelago Sea, situated in the northern Baltic Sea, consists of over 40 000 small islands and islets. It is a vulnerable area and suffers from continuous nutrient loading from the catchment and also from the background loading from the surrounding open sea areas. We studied water exchange in this complex coastal archipelago by simulating the water age and currents with a 3D hydrodynamic model COHERENS. The Archipelago Sea model setup has a horizontal resolution of c. 460 m and its boundary conditions are from a model setup that covers the whole Baltic Sea with a resolution of 3.7 km. The current fields produced with the hydrodynamic model were used to simulate the transport patterns of passive tracers through the archipelago with a Lagrangian particle model OpenDrift.

The mean water age was up to three months in the outer archipelago and up to seven months in the narrowest waterways in the inner archipelago. The effect of rivers on the water age was seen mostly only in the inner archipelago. The transport of passive tracer particles from the open sea areas, across the Archipelago Sea, mostly took place through the outer archipelago. The transport of particles from the outer archipelago towards the inner parts of the archipelago was very sensitive to the geometry and number of islands i.e. density of islands in the area. The prevailing wind direction in the area is from SW, this not being optimal for transport from the outer archipelago to the middle archipelago. For example, with the tracer particles from the southern open sea boundary, most transport to the middle archipelago was seen with SE winds. Transport further to the inner archipelago was limited only to few cases. The results show that the inner archipelago areas are relatively sheltered from transport from the open sea areas and the environmental problems there are in a high extent from local origin.

How to cite: Miettunen, E., Tuomi, L., and Myrberg, K.: Water exchange in a coastal archipelago in the northern Baltic Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18546, https://doi.org/10.5194/egusphere-egu2020-18546, 2020.

D2782 |
Erwan Garel, Luciano Júnior, Paulo Relvas, Irene Laiz, and Jesús Gómez-Enri

Satellite-derived sea level records are generally known to be unreliable in coastal zones. However, major progresses have been made during the last decade based on improved corrections and reprocessing of along-track altimeter data. In this study, altimeter-derived CryoSat-2 products are used to study the coastal circulation along the inner northern shelf of the Gulf of Cadiz, at the southern extremity of the western Iberian upwelling system. Coastal upwelling in this region results from coastal divergence due offshore Ekman transport under westerly favourable wind, and gives theoretically origin to a cross-shore pressure gradient. Upwelling activity is usually identified based on sea temperature cooling at the coast and the development of upwelling jets produced by geostrophic balance. These eastward alongshore flows alternate with westward flows (Coastal Counter Currents, CCCs) which main driver (e.g., local wind stress, geostrophic balance or alongshore pressure variations) is not definitively identified yet.

The present research proposes to get insights into the factors that drive the coastal circulation, based on the Absolute Dynamic Topography (ADT) obtained from CryoSat-2 along-track products (in SAR mode). The studied coastal stretch, about 200 km in length, is broadly oriented E-W, allowing the use of (the meridional) satellite tracks for the determination of cross-shore sea level variations. For validation, sea level oscillations from tidal gauges are compared with sea level anomalies from nearby tracks. In general, the satellite-derived sea level data reproduce adequately the temporal trends of water level variations at the coast. However, the CryoSat-2 data obtained at less than 3/5 km from the coast was discarded to reduce potential error in the magnitude of the variations.

The coastal circulation along the coast is diagnosed based on Sea Surface Temperature (SST) satellite images and in situ Acoustic Doppler Current Profilers (ADCP) observations on the inner shelf. Remarkably, the validated cross-shore sea level data show that the water level is systematically lower near the coast during periods of active coastal upwelling. The width of the sea level gradient varies between 10 and 25 km, and closely corresponds to the cold water area identified from SST images. The corresponding geostrophic flow is estimated about 0.5 m/s, similar to the observed upwelling jets near the surface. By contrast, periods with CCCs generally correspond to a flat cross-shore slope, discarding geostrophic balance as their main driver. On-going work analyses jointly CryoSat-2 tracks which are temporally closed for the determination of sea level and slope variations along the coast associated to the development of strong alongshore flows.

How to cite: Garel, E., Júnior, L., Relvas, P., Laiz, I., and Gómez-Enri, J.: Coastal circulation from along-track satellite altimetry along the northern inner shelf of the Gulf of Cadiz, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18926, https://doi.org/10.5194/egusphere-egu2020-18926, 2020.

D2783 |
Jaromir Jakacki, Maciej Muzyka, Marta Konik, Anna Przyborska, and Jan Andrzejewski

During the last decades remote sensing observations as well as modelling tools has been developed and become key elements of oceanographic research. One of the main advantages of both tools is a possibility of measuring large-scale areas.

The remote sensing measurements deliver only snapshots of the ice situation with no information about backgroundconditions. Moreover, providing picture of the whole area requires sometimes combining various datasets that increases uncertainties.  Modelling simulations provide full history of external conditions, but they also introduce errors that are the result of parameterizations. Also, an inaccuracy provided by forcing fields at the top and bottom boundaries are accumulated in the model.

In this work sea ice parameters such as sea ice concentration, thickness and volume obtained from both – satellite measurements and modelling has been compared. Numerical simulations were performed using standalone Community Ice Code (CICE) model (v. 6.0). It is a descendant of the basin scale dynamic-thermodynamic and thickness distribution sea ice model. The model is well known by scientific community and was widely used in a global as well as regional research, even operationally. The satellite derived ice thickness products were based on the C band HH-polarized SAR measurements originating from the satellites Sentinel-1 and RADARSAT-2. The sea ice concentration maps contain also visual and infrared information from MODIS and NOAA.

The ice extent, thickness and volume were compared in several regions within the Baltic Sea.  Seasonal changes were analyzed with a particular attention to ice formation and melting time. The sea ice extent datasets were compatible. Inconsistencies were observed for the sea ice thickness delivered by satellite measurements, especially during the ice melt. The work presents direction for ignoring satellite data with an error related to ice melting that allows for excluding erroneous satellite maps and obtain reliable intercalibration.


This work was partly funded by Polish National Science Centre, project number 2017/25/B/ST10/00159

How to cite: Jakacki, J., Muzyka, M., Konik, M., Przyborska, A., and Andrzejewski, J.: Comparison of the main sea ice parameters received from satellite measurements and based on numerical simulation for the Baltic Sea region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19573, https://doi.org/10.5194/egusphere-egu2020-19573, 2020.

D2784 |
| Highlight
Antonio Ricchi, Davide Bonaldo, Mario Marcello Miglietta, and Sandro Carniel

The Mediterranean basin is the formation site of a vast number and type of cyclones. Among these, we can occasionally identify intense vortices showing tropical characteristics, called Tropical-Like Cyclones (TLC) or MEDIcanes (Mediterranean Hurricane). Their development has been studied in several case studies, showing the influence of synoptic scale upper level forcings and mesoscale features, such as the sea surface temperature and the characteristics of the air masses on the formation area. The importance of Sea Surface Temperature (SST) consists in modulating the intense latent and sensible heat fluxes, which control the development of the TLC. For tropical cyclones, one of the most studied factors in recent years is the ocean heat content in the formation basin of these storms. We plan here to extend this analysis to TLC. Besides innovative studies with coupled atmosphere-waves-ocean numerical models, a simpler approach for investigating the sole effect of the ocean heat content consists of adopting a simplified ocean (1-Dimensional) description by varying the local characteristics of the Ocean Mixed Layer (OML). In this work we use the WRF (Weather Research and Forecasting system) model, in standalone (atmospheric) mode, with 3 km grid spacing, forced with GFS-GDAL (0.25°x0.25° horizontal resolution) and SST initialization provided by the MFS-CMEMs Copernicus dataset. Three case studies of TLC are examined here, namely ROLF (06-09/11/2011), ILONA (19-21/01/2014) and NUMA (11-20/11/2017). The ocean is simulated with an OML approach, with SST updated at each iteration as a function of the atmospheric heat fluxes and with an average mixed layer deph (MDL) provided by the MFS-CMEMS dataset. For each TLC studied, the MDL is modified by increasing and decreasing its depth by 50% and increasing and decreasing its lapse rate by 50%. The results show how the structure of the MDL influences not only the intensity of the cyclone but also the structure and precipitation both in terms of quantity and location. These outcomes suggest that, as for hurricanes, also for MEDICANES the heat content of the mass of seawater plays a fundamental role in their intensification, suggesting further studies also in a climate change perspective.

How to cite: Ricchi, A., Bonaldo, D., Miglietta, M. M., and Carniel, S.: On the Ocean Mixed Layer influence on the genesis of Mediterranean Tropical-Like cyclones, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22001, https://doi.org/10.5194/egusphere-egu2020-22001, 2020.