International audienceHigh-frequency (HF) coastal radars measure current velocity at the ocean surface with a 30-100 km range and 1-3 km resolution, every 0.25-1 h. HF radars are well suited to many applications, such as search and rescue (SaR), oil-spill mitigation and ecosystem management. Here we present a first organized core of 12 HF radars installed in five sites in four countries (Greece, Italy, France and Spain) within the European MED project, the Tracking Oil Spill and Coastal Awareness (TOSCA) network. Dedicated experiments tested radar capabilities to estimate transport driven by currents, which is the key feature for all the above applications. Experiments involved the deployment of drifters, i.e., floating buoys, acting as proxies for substances passively advected by currents. Using HF radars the search range is reduced by a factor of 1.6 to 5.3 after 24 h. The paper also underlines the importance of sharing common tools for HF radar data processing and the need to mitigate radio frequency interference. The effort can be regarded as an initial step toward the creation of a Mediterranean or European HF radar network, crucial for any European integrated ocean observing system (IOOS)
<p>The coastal marine ecosystem of Saronikos Gulf, a busy Eastern Mediterranean embayment directly impacted by the greater metropolitan area of Greece&#8217;s capital, Athens, is examined through a series of state-of-the-art numerical models that address the hydrodynamics (Delft3D-FLOW), the wave regime (SWAN), the biogeochemistry, and pollution related to species of heavy metals and polyaromatic hydrocarbons (Delft3D-WAQ).</p>
<p>The study so far has focused on calibrating model components and on reproducing the seasonal thermohaline conditions, known circulation patterns and the variability of biogeochemical constituents (chlorophyll-a, nutrients, dissolved and particulate matter) and pollutant concentrations, focusing on the vicinity of inner Saronikos.</p>
<p>The annual cycle &#8216;Nov 2009 - Oct 2010&#8217; is simulated, forced with atmospheric data from the ERA5 database. Three sets of open boundary conditions data are tested (Mediterranean Sea Physics Reanalysis dataset by Copernicus and two implementations of the ROMS model covering the Aegean and the Eastern Mediterranean respectively), constituting three classes of numerical experiments aiming to optimize model performance. Freshwater discharges from waste treatment facilities and rivers are considered, the latter drawn from the Swedish Meteorological and Hydrological Institute (platform &#8216;Hypeweb&#8217;).</p>
<p>Emphasis has been placed in compiling available information on point sources of pollution from the numerous human activities in the vicinity of the study area. These data are used as forcing in the modelling process.</p>
<p>A comprehensive dataset of field measurements collected monthly by the Hellenic Centre for Marine Research from a network of ten stations, as well as satellite derived SST data, are used for model validation.</p>
<p>This work is carried out within the context of the EMERGE Horizon 2020 project, that develops methodologies to evaluate, control and mitigate the environmental impacts of shipping emissions. For the scope of the project, next steps currently undertaken include the simulation of the Saronikos Gulf status for the year 2018 considering pollutant mass fluxes (a) from shipping emissions as calculated by the Ship Traffic Emission Assessment Model (STEAM) and (b) from atmospheric depositions as calculated from atmospheric modelling, both components from data provided by consortium partners.</p>
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The combined effects of weak compressibility and viscoelasticity in steady, isothermal, laminar axisymmetric Poiseuille flow are investigated. Viscoelasticity is taken into account by employing the Oldroyd-B constitutive model. The fluid is assumed to be weakly compressible with a density that varies linearly with pressure. The flow problem is solved using a regular perturbation scheme in terms of the dimensionless isothermal compressibility parameter. The sequence of partial differential equations resulting from the perturbation procedure is solved analytically up to second order. The two-dimensional solution reveals the effects of compressibility and the other dimensionless numbers and parameters in the flow. Expressions for the average pressure drop, the volumetric flow rate, the total axial stress, as well as for the skin friction factor are also derived and discussed. The validity of other techniques used to obtain approximate solutions of weakly compressible flows is also discussed in conjunction with the present results.
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