1,721,178 research outputs found
Modelling study of transformations of the exchange flows along the Strait of Gibraltar
No full textVertical transfers of heat, salt and mass between the inflowing and outflowing layers at the Strait of Gibraltar are explored basing on the outputs of a three-dimensional fully nonlinear numerical model. The model covers the entire Mediterranean basin and has a very high spatial resolution around the strait (1/200ĝ). Another distinctive feature of the model is that it includes a realistic barotropic tidal forcing (diurnal and semi-diurnal), in addition to atmospheric pressure and heat and water surface fluxes. The results show a significant transformation of the properties of the inflowing and outflowing water masses along their path through the strait. This transformation is mainly induced by the recirculation of water, and therefore of heat and salt, between the inflowing and outflowing layers. The underlying process seems to be the hydraulic control acting at the Espartel section, Camarinal Sill and Tarifa Narrows, which limits the amount of water that can cross the sections and forces a vertical recirculation. This results in a complex spatio-Temporal pattern of vertical transfers, with the sign of the net vertical transfer being opposite in each side of the Camarinal Sill. Conversely, the mixing seems to have little influence on the heat and salt exchanged between layers (ĝ1/42 %-10 % of advected heat and salt). Therefore, the main point of our work is that most of the transformation of water properties along the strait is induced by the vertical advection of heat and salt and not by vertical mixing. A simple relationship between the net flux and the vertical transfers of water, heat and salt is also proposed. This relationship could be used for the fine-Tuning of coarse-resolution model parameterizations in the strait. © 2018 Author(s)
Investigation of model capability in capturing vertical hydrodynamic coastal processes: A case study in the north Adriatic Sea
No full textIn this work we consider a numerical study of hydrodynamics in the coastal zone using two different models, SHYFEM (shallow water hydrodynamic finite element model) and MITgcm (Massachusetts Institute of Technology general circulation model), to assess their capability to capture the main processes. We focus on the north Adriatic Sea during a strong dense water event that occurred at the beginning of 2012. This serves as an interesting test case to examine both the models strengths and weaknesses, while giving an opportunity to understand how these events affect coastal processes, like upwelling and downwelling, and how they interact with estuarine dynamics. Using the models we examine the impact of setup, surface and lateral boundary treatment, resolution and mixing schemes, as well as assessing the importance of nonhydrostatic dynamics in coastal processes. Both models are able to capture the dense water event, though each displays biases in different regions. The models show large differences in the reproduction of surface patterns, identifying the choice of suitable bulk formulas as a central point for the correct simulation of the thermohaline structure of the coastal zone. Moreover, the different approaches in treating lateral freshwater sources affect the vertical coastal stratification. The results indicate the importance of having high horizontal resolution in the coastal zone, specifically in close proximity to river inputs, in order to reproduce the effect of the complex coastal morphology on the hydrodynamics. A lower resolution offshore is acceptable for the reproduction of the dense water event, even if specific vortical structures are missed. Finally, it is found that nonhydrostatic processes are of little importance for the reproduction of dense water formation in the shelf of the north Adriatic Sea. © 2016 Author(s)
How much do tides affect the circulation of the Mediterranean Sea? From local processes in the Strait of Gibraltar to basin-scale effects
No full textThe effects of tidal forcing on the exchange flow through the Strait of Gibraltar and the circulation in the near-field region are revisited with a regional numerical model. Also a basin-scale model run is conducted in a first attempt to assess the impact of these local processes on the Western Mediterranean thermohaline circulation. In the Strait of Gibraltar, tides are found to (1) increase the exchange flow volume transport, (2) modify the hydrological properties of Atlantic inflowing waters through the enhancement of mixing, and (3) facilitate the drainage of Mediterranean deep water. In the far-field, the model reveals that these local processes can favor deep convection in the Gulf of Lion. Some thoughts are provided offering possible explanations
The interface mixing layer and the tidal dynamics at the eastern part of the Strait of Gibraltar
No full textA non-hydrostatic numerical model forced by tides has been adapted to the Strait of Gibraltar area to investigate the dynamics of the interface layer in the eastern part of the strait, namely the area that extends from the main sill of Camarinal to the eastern exit of the strait. The model reproduces the tidal oscillations of the interface thickness and the mean depth, showing that the westward barotropic tide raises the interface and reduces its thickness, thus being the physical mechanism that re-stratifies the water column. Several processes are involved in the thickening and sinking tidal phase of the interface: (1) the eastward horizontal advection from Tangier basin, located west of Camarinal sill, where the huge dissipation associated with hydraulic transitions generates a remarkable mixing layer, (2) entrainment as the interface waters progress towards the Mediterranean Sea and (3) internal friction associated with the large amplitude internal waves radiated into the Mediterranean. Some biologically-related implications of the interface dynamics are also examined. © 2013 Elsevier B.V
Exchange flow through the strait of gibraltar as simulated by a s-coordinate hydrostatic model and a z-coordinate nonhydrostatic model
No full text[No abstract available
The Mediterranean Sea heat and mass budgets: Estimates, uncertainties and perspectives
No full textThis paper presents a review of the state-of-the-art in understanding and quantification of the Mediterranean heat and mass (i.e. salt and water) budgets. The budgets are decomposed into a basin averaged surface component, lateral boundary components (through the Gibraltar and the Dardanelles Straits), a river input component and a content change component. An assessment of the different methods and observational products that have been used to quantify each of these components is presented. The values for the long term average of each component are also updated based on existing literature and a first estimate of heat fluxes associated with the riverine input has been produced. Special emphasis is put on the characterization of associated uncertainties and proposals for advancing current knowledge are presented for each budget component. With the present knowledge of the different components, the Mediterranean budgets can be closed within the range of uncertainty. However, the uncertainty range remains relatively high for several terms, particularly the basin averaged surface heat fluxes. Consequently, the basin averaged heat budget remains more strongly constrained by the Strait of Gibraltar heat transport than by the surface heat flux. It is worth remarking that if a short (∼few years) averaging period is used, then the heat content change must also be considered to constrain the heat budget. Concerning the water and salt fluxes, the highest uncertainties are found in the direct estimates of the Strait of Gibraltar water and salt transport. Therefore, the indirect estimate of those transports using the budget closure leads to smaller uncertainties than the estimates based on direct observations. Finally, estimates of Mediterranean heat and salt content trends are also reviewed. However, these cannot be improved through the indirect estimates due to the large temporal uncertainties associated to the surface fluxes and the fluxes through Gibraltar. The consequences of these results for estimates of the Mediterranean temperature and salinity trends obtained from numerical modelling are also considered. © 2017 Elsevier Lt
Unexpected Covariant Behavior of the Aegean and Ionian Seas in the Period 1987–2008 by Means of a Nondimensional Sea Surface Height Index
No full textIn this work, we use a set of recent multiyear simulations to develop a simplified sea surface height index (SSH). The index characterizes the dynamics of Ionian upper layer circulation and its links with sea surface height and salinity in the Southern Adriatic and Aegean Seas during the period 1987–2008. The analysis highlights a covariant behavior between Ionian Sea and Aegean Sea associated with a mutual zonal exchange of water masses with different salinity characteristics. Our analysis confirms that the variability observed in the period 1987–2008 in the upper layer circulation of the Ionian was driven by the salinity variability in the Southern Adriatic and Aegean Sea. This study supports and reinforces the hypothesis that two observed BiOS-like reversals reflect the existence of multiple equilibrium states in the Mediterranean Thermohaline circulation in the Eastern Mediterranean and that a complete characterization of observed variability needs to take into account a fully coupled Adriatic-Ionian-Aegean System. © 2017. American Geophysical Union. All Rights Reserved
Exchange Flow through the Strait of Gibraltar as Simulated by a σ-Coordinate Hydrostatic Model and a z-Coordinate Nonhydrostatic Model
No full textThe Mediterranean Sea is a semi-enclosed basin displaying an active thermohaline circulation that is sustained by the atmospheric forcing and controlled by the narrow and shallow Strait of Gibraltar (SoG). The main goal of this chapter is the investigation of the effects produced by certain specific factors on the simulated hydraulic behavior of the SoG by the nonhydrostatic assumption, the resolution adopted, and the parameterization used for mixing on the simulated hydraulic regime. The chapter is organized as follows. After an introductory section, two models (Princeton Ocean Model (POM) and Massachusetts Institute of Technology general circulation model (MITgcm)) are described and validated in the second and third sections. The comparison of the models in terms of the simulated internal wave field, three-layer properties, and hydraulics is shown in the fourth section. Conclusions are discussed in the last section. © 2014 American Geophysical Union
Wave climate analysis for the design of wave energy harvesters in the Mediterranean Sea
No full textThe objective of this paper is to provide a synthetic tool for determining expeditiously the wave climate conditions in several areas of the Mediterranean Sea. In the open literature, several authors have already conducted this specific analysis also for the area under examination in this paper. However, the need of discussing aspects strictly related to the design of wave energy harvesters is still relevant. Therefore, considering the variety of devices and the amount of information needed for conducting both an energy-wise optimization and a structural reliability assessment, a holistic view on the topic is provided. Specifically, the paper elucidates the theoretical aspects involved in the estimation of wave energy statistics and in the calculation of relevant return values. Next, it provides synthetic data representing the mean wave power and the return value of extreme events in several coastal areas of the Mediterranean Sea. In this regard, the paper complements information available in the open literature by discussing the influence of the directional pattern of the sea states in the determination of sea state statistics as well as in the design of a wave energy harvester. © 2014 Elsevier Ltd
Present climate wave energy potential along the Western Sardinia coast (Italy)
No full textA wave energy atlas for the west coast of Sardinia is presented. Energy has been computed from a 10 year simulation performed using a third generation wave model at the spatial resolution of 1/120°. A detailed analysis of energy results has been performed in three points at different distances from the coast. © 2013 IEEE
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