Dynamics of the Baltic Sea straits via numerical simulation of exchange flows

Stanev, Emil V.; Pein, Johannes; Grashorn, Sebastian; Zhang, Y.; Schrum, Corinna

doi:10.1016/j.ocemod.2018.08.009

Cited by 25 publications

(14 citation statements)

References 49 publications

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“…hydrodynamic conditions with very high resolution, on the horizontal, vertical and temporal dimensions. With respect to the above-cited requirement, unstructured models -as the one applied in this study -realise a seamless transition between different spatial scales for reproducing the coastal-sea interactions, adopting a variable resolution of the mesh elements (Ferrarin et al, 2018;Kärnä et al, 2018;Maicu et al, 2018;Stanev et al, 2018;Androsov et al, 2019). The applied numerical models need to be continuously evaluated and upgraded to maintain the highest accuracy.…”

Section: Discussionmentioning

confidence: 99%

Model-driven optimization of coastal sea observatories through data assimilation in a finite element hydrodynamic model (SHYFEM v.7_5_65)

Ferrarin¹,

Bajo²,

Umgiesser³

2020

Preprint

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Abstract. Monitoring networks aims at capturing the spatial and temporal variability of one or several environmental variables in a specific environment. The optimal placement of sensors in an ocean or coastal observatory should maximize the amount of collected information and minimize the development and operational costs for the whole monitoring network. In this study, the problem of the design and optimization of ocean monitoring networks is tackled throughout the implementation of data assimilation techniques in the Shallow water Hydrodynamic Finite Element Model (SHYFEM). Two data assimilation methods – Nudging and Ensemble Square Root Filter – have been applied and tested in the Lagoon of Venice (Italy), where an extensive water level monitoring network exists. A total of 29 tide gauge stations were available and the assimilation of the observations result in an improvement of the performance of the SHYFEM model that went from an initial root mean square error (RMSE) on the water level of 5.8 cm to a final value of about 2.1 and 3.2 cm for the two data assimilation methods, respectively. In the monitoring network optimization procedure, by excluding just one tide gauge at a time, and always the station that contributes less to the improvement of the RMSE, a minimum number of tide gauges can be found that still allow for a successful description of the water level variability. Both data assimilation methods allow identifying the number of stations and their distribution that correctly represent the state variable in the investigated system. However, the more advanced Ensemble Square Root Filter has the benefit of keeping a physically and mass conservative solution of the governing equations, which results in a better reproduction of the hydrodynamics over the whole system. In the case of the Lagoon of Venice, we found that, with the help of a process-based and observation-driven numerical model, two-thirds of the monitoring network can be dismissed. In this way, if some of the stations must be decommissioned due to a lack of funding, an a-priori choice can be made, and the importance of the single monitoring site can be evaluated. The developed procedure may also be applied to the continuous monitoring of other ocean variables, like sea temperature and salinity.

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Section: Discussionmentioning

confidence: 99%

Model-driven optimization of coastal sea observatories through data assimilation in a finite element hydrodynamic model (SHYFEM v.7_5_65)

Ferrarin¹,

Bajo²,

Umgiesser³

2020

Preprint

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“…In more recent studies on the two-layer exchange in the interconnection zone between the Baltic Sea and the North Sea (a system similar to the cascade described above), the authors of [14,44] studied the secondary circulation in the Danish Straits based on observations and numerical modelling using an unstructured-grid hydrodynamic model. They demonstrated that with a resolution of ∼ 100 m in the straits, new transport and mixing pathways appear, which are fundamental to the strait dynamics.…”

Section: The Narrow Ocean Straits 1 the Cascade From The Azov Sea Tomentioning

confidence: 99%

Numerical Eddy-Resolving Modeling of the Ocean: Mesoscale and Sub-Mesoscale Examples

Stanev

Ricker

Grayek

et al. 2020

PhO

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The study addresses rotational motion of geophysical fluids in the horizontal and vertical planes. It is aimed mainly at tracing the development of high-resolution numerical modeling of the ocean, as well as at demonstrating new physical processes due to more correct consideration both of the tides in the eddy-resolving numerical models and sub-mesoscale dynamics in the models of the sea straits. Methods and Results. The ocean eddies and their interaction with tides are studied using numerical simulations by four NEMO models for the European NorthWest shelf with the resolutions ranging from 7 to 1.5 km. The vertical characteristics of motion in the Bosporus Strait were studied using numerical simulations with SCHISM, the unstructured grid model with the ultra-fine model resolution (less than 100 m). The barotropic tidal forcing resulted in substantial flattening of the slopes of the spectral curves. The most important difference between the spectral features of four models occurs in the motion rotational component. In the model with the 1.5 km resolution, the magnitude of the vorticity power spectral density at the scales ~ 70 km is by an order of magnitude higher than in the other three models. Although most of the tidal flattening is associated with the internal tides, beyond a certain horizontal resolution, the eddy dynamics become affected by the barotropic tides. The shelf of the Biscay Bay and the shallows around the Faroe Islands are the most sensitive areas to adding of the barotropic tides to the model forcing. Due to the grid ultra-fine resolution, new elements of physical motion emerged in the Bosporus region. The lateral circulation is dominated by the systems of multiple circulation cells with the scales ~ 1 km. In some areas, the lateral flow magnitude exceeds 0.5 m/s, which is comparable with the magnitude of the axial flow. This reveals importance of the helical elements of the strait circulation for overturning of water masses in the Bosporus. Conclusions. Without proper resolution, the models of tidal oceanic dynamics simulate the ocean general circulation, but do not describe correctly the energy cascades at the eddy scales including interaction between the tides and the mesoscale eddies. Absence of this sub-mesoscale dynamics in the models can largely affect their capability to simulate the two-layer inter-basin exchange.

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“…В более поздних исследованиях двухслойного обмена в зоне соединения Балтийского и Северного морей (система, подобная каскаду, описанному выше) авторы работ [14,44] исследовали вторичную циркуляцию в датских проливах на основе наблюдений и численного моделирования с использованием гидродинамической модели с неструктурированной сеткой. Они продемонстрировали, что при разрешении ∼ 100 м в проливах появляются новые пути переноса и перемешивания, которые имеют фундаментальное значение для динамики пролива.…”

Section: узкие океанские проливы 1 каскад от азовского к средиземномunclassified

Numerical Eddy-Resolving Modeling of the Ocean: Mesoscale and Sub-Mesoscale Examples

Stanev¹,

Ricker²,

Grayek³

et al. 2020

MGZh

View full text Add to dashboard Cite

The study addresses rotational motion of geophysical fluids in the horizontal and vertical planes. It is aimed mainly at tracing the development of high-resolution numerical modeling of the ocean, as well as at demonstrating new physical processes due to more correct consideration both of the tides in the eddy-resolving numerical models and sub-mesoscale dynamics in the models of the sea straits. Methods and Results. The ocean eddies and their interaction with tides are studied using numerical simulations by four NEMO models for the European North-West shelf with the resolutions ranging from 7 to 1.5 km. The vertical characteristics of motion in the Bosporus Strait were studied using numerical simulations with SCHISM, the unstructured grid model with the ultra-fine model resolution (less than 100 m). The barotropic tidal forcing resulted in substantial flattening of the slopes of the spectral curves. The most important difference between the spectral featurws of four models occurs in the motion rotational component. In the model with the 1.5 km resolution, the magnitude of the vorticity power spectral density at the scales ~70 km is by an order of magnitude higher than in the other three models. Although most of the tidal flattening is associated with the internal tides, beyond a certain horizontal resolution, the eddy dynamics become affected by the barotropic tides. The shelf of the Biscay Bay and the shallows around the Faroe Islands are the most sensitive areas to adding of the barotropic tides to the model forcing. Due to the grid ultra-fine resolution, new elements of physical motion emerged in the Bosporus region. The lateral circulation is dominated by the systems of multiple circulation cells with the scales ~ 1 km. In some areas, the lateral flow magnitude exceeds 0.5 m/s, which is comparable with the magnitude of the axial flow. This reveals importance of the helical elements of the strait circulation for overturning of water masses in the Bosporus. Conclusions. Without proper resolution, the models of tidal oceanic dynamics simulate the ocean general circulation, but do not describe correctly the energy cascades at the eddy scales including interaction between the tides and the mesoscale eddies. Absence of this sub-mesoscale dynamics in the models can largely affect their capability to simulate the two-layer inter-basin exchange.

show abstract

Dynamics of the Baltic Sea straits via numerical simulation of exchange flows

Cited by 25 publications

References 49 publications

Model-driven optimization of coastal sea observatories through data assimilation in a finite element hydrodynamic model (SHYFEM v.7_5_65)

Model-driven optimization of coastal sea observatories through data assimilation in a finite element hydrodynamic model (SHYFEM v.7_5_65)

Numerical Eddy-Resolving Modeling of the Ocean: Mesoscale and Sub-Mesoscale Examples

Numerical Eddy-Resolving Modeling of the Ocean: Mesoscale and Sub-Mesoscale Examples

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