Acoustic Doppler Current Profiler (ADCP) and Expendable Bathy Thermograph (XBT) data were collected during the Latex08 cruise (September 1–5, 2008) throughout the western part of the Gulf of Lion. ...These data, combined with Sea Surface Temperature (SST) satellite images and Lagrangian drifter trajectories, show the presence of an intense anticyclonic eddy in the western part of the Gulf of Lion. The eddy is elliptic in shape and the estimated radius is 21.5 (15.5) km for its major (minor) axis. The vertical extent of the eddy reached about 35
m depth and was limited by the bottom of the seasonal mixed layer. The eddy interacts with the Northern Current at the end of the cruise, maybe leading to its deformation. Moreover complementary drifter data suggest that this anticyclonic eddy was already present at the beginning of August 2008. Hence the eddy lasted around 50
days in the same region. In light of previous numerical study, some hypotheses about the formation and behavior of the eddy are also discussed.
► We study an observed eddy structure in the western part of the Gulf of Lion during the Latex08 cruise. ► We use ADCP, XBT, SST data and Lagrangian drifters to investigate the observed eddy. ► This coastal mesoscale anticyclonic eddy is elliptic in shape, and baroclinic, limited vertically to the thermocline. ► The coastal eddy can interact with the large scale circulation. ► We propose some mechanisms of eddy generation.
We investigate the dynamics of a coastal anticyclonic eddy in the western part of the Gulf of Lion (GoL) in the northwestern Mediterranean Sea during the Latex campaign in the summer 2009 (Latex09). ...The sampling strategy combines sea surface temperature satellite imagery, hull‐mounted acoustic Doppler current profiler data, conductivity‐temperature‐depth casts, and drifter trajectories. Our measurements reveal an anticyclonic eddy (Latex09 eddy) with a diameter of ~23 km and maximum depth of 31 m, centered at 3°34′E, 42°33′N. We use a high resolution, three‐dimensional, primitive equation numerical model to investigate its generation process and evolution. The model is able to reproduce the observed eddy, in particular its size and position. The model results suggest that the Latex09 eddy is induced by a large anticyclonic circulation in the northwestern part of the GoL, pushed and squeezed toward the coast by a meander of the Northern Current. This represents a new generation mechanism that has not been reported before. The post generation dynamics of the eddy is also captured by the model. The collision of the Latex09 eddy with Cape Creus results in a transient structure, which is depicted by the trajectories of two Lagrangian drifters during Latex09. The transient structure and its advection lead to a transfer of mass and vorticity from the GoL to the Catalan shelf, indicating the importance of mesoscale structures in modulating such exchanges in the region.
Key Points
Coastal eddies
In situ measurements
Numerical modeling
A realistic numerical model is used to investigate the generation process of anticyclonic eddies located in the western part of the Gulf of Lion. During 8 years of simulations from 2001 to 2008, 8 ...anticyclonic coastal eddies with a life duration longer than 15 days have been observed in the study area between July and early October. The formation process of eddies is linked to the wind stress curl in the area. Nonetheless a simpler criteria can be used examining the changes in the wind amplitude at a key coastal station. The influences of this factor and of the stratification conditions over the study area are investigated, alone or combined, regarding the eddy's formation process. Our results show that these eddies need two conditions to be generated: a persistent and strong northwest wind and a strong stratification. The Ekman transport associated to such a wind and the coastline shape characterized by the presence of capes can create a pressure gradient generating an anticyclonic circulation. At the same time, a strong stratification condition allows a better transfer of wind‐induced potential energy to eddy kinetic energy. Persistent wind bursts are also required to sustain the eddy in size and intensity. The present work contributes to a better understanding of the hydrodynamics of the Gulf of Lion.
Key Points
Study of coastal eddies in the GoL based on long term numerical simulation
Coastal eddy fomation process
Investigate combined effect of wind and stratification condition
The diet of shortfin makos (Isurus oxyrinchus) and blue sharks (Prionace glauca) were studied by analyzing stomach contents of specimens captured by longliners near the Azores Archipelago and between ...the Azores and the Iberian Peninsula. The diet of the shortfin mako is strongly dominated by teleosts (mainly Scomberesox saurus), while that of the blue shark is strongly dominated by cephalopods (mainly Histioteuthis sp.). In mass of non-reconstituted prey, sea mammals play an important role, especially for the blue shark. Downloads/671-04_Biton_Porsmoguer.pdf.
The eastern Mediterranean (Levantine Basin) hydrography and circulation are investigated by comparing the results of a high-resolution primitive equation model with observations. After a 10-year ...integration, the model is able to reproduce the major water masses and the circulation patterns of the eastern Mediterranean. Comparisons with the POEM hydrographical observations show good agreement. The vertical distribution of the water masses matches that of the observations quite well in terms of monthly mean. The model surface circulation is in agreement with circulation schemes derived from recent observations. Some well-known mesoscale features of the upper thermocline circulation are also realistically reproduced. In agreement with satellite observations, the model shows that high-energy mesoscale eddies dominate the upper thermocline circulation in the southern and the central parts of the Levantine Basin. Most of the Atlantic Water follows the north African coast and forms a strong coastal jet near the Libyan coast rather than forming the Mid-Mediterranean Jet described by several authors. The sub-basin circulation shows a strong seasonal signal. A strong and stable current flows along the isobaths in winter, becoming weaker and with more meanders in summer. The mesoscale eddies throughout the whole basin are more energetic in summer than in winter.
We present realistic simulations of mesoscale anticyclonic eddies, present in the western side of the Gulf of Lion and generally observed in satellite imagery during July and August. A nested model ...of 1-km resolution covering the Gulf of Lion is implemented from a coarse model of 3-km resolution. The models use an upwind-type advection–diffusion scheme, in which the numerical diffusion term is adjusted by an attenuation coefficient. Sensitivity tests have been carried out, varying the model spatial resolution and the attenuation coefficient to reproduce the (sub)mesoscale structures. A wavelet technique is applied to analyze the modelled horizontal relative vorticity in order to define the area, position and tracking duration of the eddy structures. Comparisons between the modelled eddies and those observed by satellite have allowed us to choose the best model setup. With this setup, the studied anticyclonic eddy lasted for 60
days.
Tidal propagation in Ria de Aveiro Lagoon, Portugal Dias, J.M.; Lopes, J.F.; Dekeyser, I.
Physics and chemistry of the earth. Part B, Hydrology, oceans and atmosphere,
1/2000, Letnik:
25, Številka:
4
Journal Article
Recenzirano
Ria de Aveiro is a shallow vertically homogeneous lagoon, located in the Northwest of Portugal, connected to the Atlantic through a very narrow artificial channel, and supplied with freshwater by two ...major rivers, Antua and Vouga. The present study describes the application of a two-dimensional depth integrated mathematical model, to predict tide-induced water level and depth mean current for the entire lagoon. The model computes time series of those variables as well as their instantaneous distribution at different times of the tidal cycle. Properties of tides and tidal currents in Ria de Aveiro are characterized and discussed. Special emphasis is given to the study of the hydrodynamic behaviour of the lagoon in extreme conditions of astronomical tide forcing, considering spring and neap tide conditions. Tides propagate from the mouth of Ria de Aveiro and are present in the entire lagoon. The tidal amplitude decreases with the distance from the mouth while the phase lag in the high and low water (which is different) increases. The tidal range increases for the spring tide at the far end of the channels correspond to a local increase of the high tide level, which result in a fortnightly variation of the mean levels at those places.
A plankton functional types model forced by a hydrodynamic model is used in the present work to study the impacts of a coastal eddy on the distribution of nutrients and plankton in the western part ...of Gulf of Lion (NW Mediterranean Sea). This study, based on a realistic simulation of the year 2001, focuses on a long-life anticyclonic eddy detected during summer. The studied anticyclonic eddy has some biogeochemical characteristics of those observed in the open ocean as for example the low productivity at their core and rising-up of nutricline on their edges. However the functioning and consequences of such coastal eddy on nutrients and plankton distributions are complicated by potential interactions with topography, wind-induced upwelling along the Languedoc Coast and nearby Northern Current (NC). Especially the proximity of the southern edge of the eddy with the NC makes possible the exchanges of organic matter (e.g. plankton) at times during the eddy’s life. The coastal eddy thus transports organic matter from the coastal zone to the offshore domain. The coupled model also suggests the importance of offshore-to-coastal transport by NC through a seeding process of the eddy in plankton at the beginning of its life. A detailed biogeochemical functioning of the studied eddy all along its lifetime is proposed from the model results. At the beginning the eddy mainly acts as a transporter of the plankton wind-induced bloom occurring along the Languedoc Coast several days before the eddy set up. At the same time the eddy shows upwards vertical velocities on its edges creating upwelling of nutrient-enriched waters. The process of eddy-induced upwelling is notably enhanced on the eddy western side along the Roussillon Coast due to the shelf topography. The around-eddy advection and relative lower temperatures prevent the large development of phytoplankton along the Roussillon Coast and the eddy-induced bloom is predicted to occur near the northwestern side of the eddy. The eddy-induced and wind-induced blooms of phytoplankton then merge on the eastern side by advection and this process of aggregation may explain the persistent occurrence of a filament of high chlorophyll observed on the offshore edge of the eddy throughout the study period. The changes in plankton composition due to a combination of top-down and bottom-up processes during the coast-to-offshore transport may explain the disappearance of the filament south of 43°N at the surface.
A search for high-energy neutrinos coming from the direction of the Galactic Centre is performed using the data recorded by the ANTARES neutrino telescope from 2007 to 2012. The event selection ...criteria are chosen to maximise the sensitivity to possible signals produced by the self-annihilation of weakly interacting massive particles accumulated around the centre of the Milky Way with respect to the atmospheric background. After data unblinding, the number of neutrinos observed in the line of sight of the Galactic Centre is found to be compatible with background expectations. The 90% C.L. upper limits in terms of the neutrino+anti-neutrino flux, $\rm \Phi_{\nu_{\mu}+\bar{\nu}_\mu}$, and the velocity averaged annihilation cross-section, $\rm <\sigma_{A}v>$, are derived for the WIMP self-annihilation channels into $\rm b\bar{b},W^{+}W^{-},\tau^{+}\tau^{-},\mu^{+}\mu^{-},\nu\bar{\nu}$. The ANTARES limits for $\rm <\sigma_{A}v>$ are shown to be the most stringent for a neutrino telescope over the WIMP masses $\rm 25\,GeV < M_{WIMP} < 10\,TeV$.
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