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RESEARCH PROJECTS CORIOLIS PLATFORM

The projects detailed below are considered as the access to the Coriolis Platform, that are complementary to my research and belong to collaborations born on the base of the interest of external researcher to access the Platform.

21CYPROSS - BAROTROPIC ROSSBY WAVES IN A HOMOGENEOUS AND A NEARLY STRATIFIED ROTATING FLOW : THE CASE OF THE CYPRUS EDDY IN THE EASTERN MEDITERRANEAN


The laboratory experiment at the Coriolis Platform is motivated by previous oceanographic studies in the Levantine Basin. Field campaigns, in-situ measurements and numerical simulations revealed the presence of an anticyclonic eddy called Cyprus eddy which forms south of the island of Cyprus and could have a life also of two years. Its center varies between 32° - 42.5°E and the radius is approximately 50 km. Gliders observations conducted in 2017 by the National Institute of Oceanography and Applied Geophysics (OGS) group (Mauri et al., 2019) along with other previous studies (Zodiatis et al., 2005 ; Bosse et al., 2016) have shown that the Cyprus eddy extends from the surface up to 800 m of depth and locates above the Eratosthenes seamount whose summit depth is 700 m over a water depth of 2500 m. On the right side of the Cyprus eddy, a smaller cyclonic eddy (named South Shikmona Eddy - SSE) and an anticyclonic eddy (named North Shikmona Eddy -NSE) also appears. 

According to the analytical solution of McCartney 1975, on a beta plane, when an eastward flow impinges over an isolated bump, an anticyclonic Taylor column will form over it and lee waves behind. If the height of the obstacle is tall enough, additional cyclonic end anticyclonic eddies will from in wake downstream. For highly stratified flow, the solution gives bottom trapped waves (no wave-solution is given at the surface) while, for moderate stratified fluid the disturbances weaken towards the surface.


The aim of the laboratory experiment is to prove that the Cyprus eddy observed in the Levantine Basin is a Taylor column trapped over the Eratosthenes seamount and it is generated by the eastward flow. Additionally, the SSE and NSE are associated to the wake that forms behind the Cyprus eddy.

Project Leader : Annunziata PIRRO, PhD, INOGS, Trieste, Italy

Members : 
 Elena MAURI, PhD, INOGS, Trieste, Italy 
 Pierre Marie POULAIN, OGS, CMRE, Italy 
 Eletta NEGRETTI, LEGI, Grenoble  
 Samuel VIBOUD, LEGI, Grenoble  
 Thomas VALRAN, LEGI, Grenoble 

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20LEMAN : FLOW AND MIXING PROCESSES IN THE PLUNGING OF A DENSE RIVERINE INFLOW IN A WATER BODY

A hyperpycnal river plunging into a lake generates complicated 3D flow patterns and various intermediate scale coherent structures. These coherent structures have their unique 3D shapes and make significant contribution on the mixing, entrainment and detrainment processes, which is important for sediment transport, contaminant spreading and near-shore ecology.



Members :

  • Haoran Shi (PhD)

  • Andrew Barry and Ulrich Lemmin (EPFL, Switzerland),

  • Koen Blanckaert (TU Wien)

  • Eletta NEGRETTI - LEGI, France

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2019-GAPWEBS : LABORATORY MODELING OF GAP-LEAPING AND INTRUDING WESTERN BOUNDARY CURRENTS UNDER DIFFERENT CLIMATE CHANGE SCENARIOS

Western boundary currents (WBCs) are very intense currents that flow along the western boundaries of the oceans and owe their peculiar structure to the sphericity of the earth, which generates the so-called planetary beta effect. The Kuroshio and Gulf Stream (GS) are notable examples of WBCs belonging to the subtropical gyres of the North Pacific and Atlantic Oceans, respectively. The effect of WBCs and of their respective extensions on climate is well known, and is due to their huge heat transport, the corresponding air-sea interactions and the role they play in sustaining the global conveyor belt (e.g., Qiu 2000, 2003 ; Ganopolski and Rahmstorf 2002 ; Kelly et al. 2010).


One of the most interesting and intriguing WBC phenomena of climate relevance is the interaction of the jet with a gap located along the western coast. Only few studies in much smaller tanks (Kuehl and Sheremet 2009, 1m tank diameter) have been undertaken so far, but the dynamics of these currents is largely dominated by non linear effects that can be reproduced at the large Coriolis platform. Also the set-up allows for a long experimental duration that enables to study the variability of such currents.



A pumping system located in channel C produces a current of speed up that, following the lateral boundaries, generates a virtually unsheared flow at the entrance of the slope, which in turn provides the topographic beta-effect necessary for the intensification (this imposes the use of homogeneous water). The interaction of the WBC with a gap is studied by introducing the gap along the "western" boundary that can also include smaller gaps to represent islands.

Measurements techniques are based on ADV to give the initial velocity conditions (up) at the channel outlet and PIV measurements to obtain the velocity field at the western boundary and through the gap.


Project Leader :

Stefano PIERINI : University of Naples (Italy)

Member :

  • Henk A. DIJKSTRA : Utrecht University (The Netherlands)

  • Paola de RUGGIERO : Parthenope University of Naples (Italy)

  • Ilana SCHILLER WEISS : Utrecht University (The Netherlands)

  • Julia WEIFFENBACH : Utrecht University (The Netherlands)

  • Eletta NEGRETTI : LEGI (France)

  • Joël SOMMERIA : LEGI (France)

  • Samuel VIBOUD : LEGI (France)

  • Thomas VALRAN : LEGI (France)

European project Hydralab+

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18CROPEX : THE ADRIATIC-IONIAN BIMODAL OSCILLATING SYSTEM: THE CORIOLIS ROTATING PLATFORM EXPERIMENT (CROPEX)

The sense of rotation of the sub-basin-wide upper circulation in the Northern Ionian Sea (Northern Ionian Gyre) is a possible driver for deviating fresh surface Atlantic waters on their way toward the Cretan Passage to the east and toward the Adriatic Sea to the north. The reversals of this circulation on a decadal time scale (named BiOS mechanism) influence therefore the salt content of the adjacent basins, the Adriatic Sea, and Levantine basin. The salt content in turn, influences the density of the intermediate and deep waters.


The BiOS mechanism acts out-of-phase in the Adriatic and in the Levantine basin : when the Northern Ionian Gyre is anticyclonic, the flow of the Atlantic Waters towards the Levantine is deviated northward, and mixes with adjacent waters. So, it dilutes more the upper Adriatic Waters, and less the Levantine basin. When the Northern Ionian Gyre is cyclonic, the Atlantic Waters flow directly eastward toward the Cretan Passage and dilutes more the Levantine basin and less the Adriatic basin. At the same time, the Levantine and Cretan Intermediate Waters flow westward in the intermediate layer.



The physical modeling of the inversions of the Northern Ionian Gyre circulation in an idealized Adriatic-Ionian/Eastern Mediterranean circulation system at the Coriolis Rotating Platform is aimed at verifying the assumption that internal processes are crucial in driving the mechanism for the inversion of circulation of the Northern Ionian Sea, rather than the wind. In addition, the role of the turbulent eddy field in possible enforcement of the mean flow (Mid Mediterranean Jet) will be addressed and tested for the negative viscosity effect.

The experiments include measurements of the the initial dynamics of the gravity current (e.g. the Adriatic and Aegean sources of deep and intermediate waters, respectively) using Acoustic Doppler Velocimetry profilers and Conductivity probes along with measurements of the entire tank at several horizontal sections using a PIV measurement technique for the velocities and conductivity probes for the density evolution to capture the BiOS mechanism at larger time scales (>60 rotation periods).


Project Leader :

Miroslav GACIC - Istituto Nazionale di Oceanografia e di Geofisica Sperimentale - OGS, Trieste Italia

Member :

European project Hydralab+

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18JEVERB : JETS INTERACTING WITH VEGETATION IN ROTATING BASIN (JEVERB)

Contaminants, nutrients and sediment particles flow into our inland and coastal water bodies often forming turbulent jets. Some examples are outflows from rivers, sources and discharges entering the ocean through natural obstructions. Mixing processes are rather well understood for unobstructed jets, and they are mainly controlled by the initial jet characteristics, the boundary conditions and the hydrodynamic features of the ambient current. Jets obstructed by vegetation have been investigated only recently and have shown to play an important role. For example, while in the absence of vegetation the entrainment in the jet is a dominant process, the vegetation canopy has been found to induce detrainment. In the case of a uniform flow, previous research has demontrated that vegetation canopy strongly perturbs advection and dispersion depending on its density and geometry.


In realistic contexts, the effect of rotation on the turbulence induced by an obstructed pattern is felt indirectly through the modification of the mean flow, and so the subsequent transport and spreading of turbulent kinetic energy and scalars (tracers). Furtherly, rotation may induce the development of Ekman boundary layers, which effectively increases bottom friction and could alter the turbulence characteristics within the jet.


Laboratory studies investigating the effect of the earth’s rotation of a jet propagating through vegetation do not exist to date and are the goal of the present experiments. Variation parameters are the vegetation disposition and the different background rotation speeds, for a given output flow rate of the jet. Velocity fields are captured at different horizontal 2D cross sections using a PIV measurement technique, ADV point measurements and dye visualizations and will enable to obtain detailed information about the mean and turbulent flow characteristics.


Project Leader :

Francesca De Serio - Polytechnic University of Bari, Italy

Member :

European project Hydralab+

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18ADDUCE : THE DYNAMICS OF BI-DIRECTIONAL EXCHANGE FLOWS : IMPLICATION FOR MORPHODYNAMIC CHANGE WITHIN ESTUARIES AND SEA STRAITS

Environmental and geophysical flows, including dense bottom gravity currents in the ocean and buoyancy-driven exchange flows in marginal seas, are strongly controlled by topographic features. These are known to exert significant influence on both internal mixing and secondary circulations generated by these flows. In such cases, uni-directional or bi-directional exchange flows develop when horizontal density differences and/or pressure gradients are present between adjacent water bodies connected by a submerged channel. The flow dynamics of the dense lower layer depend primarily on the volumetric flux and channel cross-sectional shape, while the stratified interfacial flow mixing characteristics, leading to fluid entrainment/detrainment, are also dependent on the buoyancy flux and motion within the upper (lower density) water mass.

For submerged channels that are relatively wide compared to the internal Rossby radius of deformation, Earth rotation effects introduce geostrophic adjustment of these internal fluid motions, which can suppress turbulent mixing generated at the interface and result in the development of Ekman layers that induce secondary, cross-channel circulations, even within straight channels.

Moreover, recent studies of dense, gravity currents generated in rotating and non-rotating systems, respectively, indicated that the V-shaped channel topography had a strong influence on both flow distribution and associated interfacial mixing characteristics along the channel. However, such topographic controls on the interfacial mixing and secondary circulations generated by bi-directional exchange flows are not yet fully understood and remain to be investigated thoroughly in the laboratory.


Also the effect of mobile bed for bi-directional exchange flows generated in deformable channels along with the physical interactions between the lower dense water flow and the erodible bed sediments will have a strong influence in (re-)shaping the overall channel bed topography (i.e. bed morphodynamics). Consequently, the resulting temporal changes in cross-sectional channel bathymetry (i.e. through erosion and deposition processes) would also be expected to have associated feedbacks on transverse asymmetries in the bi-directional exchange flow structure, as well as on the internal flow stability.


Project Leader :

Claudia ADDUCE : Department of Engineering, University Roma Tre Italy

Members :

  • Alan CUTHBERSON : Heriot-Watt University, Great Britain

  • Janek LAANEARU : Tallinn University of Technology, Estonia

  • Daniela MALCANGIO : Technical University of Bari, Italy

  • Eletta NEGRETTI : LEGI, France

  • Maria-Chiara DE-FALCO : Department of Engineering, University Roma Tre Italy

European project Hydralab+

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Research Coriolis Platform: Recherche
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