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This paper investigates the mean spatial features of the winds in the Mediterranean and Black Seas using the wind fields observed by the SeaWinds scatterometer. Five years (2000–04) of data have been analyzed on annual and seasonal basis, with particular attention paid to the meso- and local scales. The fields show the existence of structured regional wind systems—in particular, the mistral in the western Mediterranean and the etesians in the Levantine Basin, which are characterized, respectively, by high wind variability and moderate steadiness and by low wind variability and high steadiness. Estimated seasonal mean wind stress τ fields show that the values falling in the top range 0.15 < τ < 0.20 N m-2 affect a large portion of the Mediterranean Basin in winter, in the belt extending from the Gulf of Lion up to the Levantine Basin and the northern Black Sea. In the other seasons, only few regions experience such high values of τ. The analysis of the wind vorticity shows and quantifies the main cyclonic and anticyclonic circulations, and the study of the joint features of wind stress and vorticity has identified the strongest and most persisting local-scale wind circulations produced by the interaction between the wind flow and the orography. They occur at the lee side of Sardinia–Corse and Crete–Rhodos Islands and persist in all seasons, with some seasonal variation in strength and extent. The areas affected by the orographic disturbances are characterized by high values of wind stress and by a structure of vorticity showing alternating areas of cyclonic and anticyclonic circulations, whose strength is comparable to those of the regional-scale cyclones. [ABSTRACT FROM AUTHOR]

Abstract: The Arctic Oscillation (AO) has been found in previous studies to be a major synoptic factor affecting the climate of many regions in the high and mid-latitudes. This paper demonstrates the physical process by which the AO affects the climate of the Eastern Mediterranean basin, with a focus on precipitation in Israel as a case study. It is shown that a trend of increasing AO is associated with a substantial decrease of winter precipitation from the Iberian Peninsula, though Italy, Greece, Turkey and Cyprus, as well as Lebanon, Syria and also the northern parts of Israel. Winter rain is slightly increased in the southern coast of the eastern half of the Mediterranean Sea. The immediate meteorological causes are shown to be a larger northerly component of the flow over the Mediterranean Sea, associated with a decreasing relative humidity and stability, except over the southern coast, where the air mass has the longest track over the relatively warm water. We suggest here that the observed changes in air flow that drives the precipitation trends can be explained by shifts in the AO that can be partially explained by increasing greenhouses gases. Results from the IPCC multi climate models show that the AO will continue to increase during the 21st century. This increase may lead to a continuation of the trends discussed here. The importance of the analysis provided here is in pointing out the possibility that processes that have been predicted by global warming and changes in global circulation have already started to affect precipitation and major water resources in the Mediterranean basin. [Copyright &y& Elsevier]

Seven years of combined maps of TOPEX/Poseidon (T/P) and ERS-1/2 altimeter data are used to describe the surface circulation variability in the Mediterranean Sea. As described in the past, the Mediterranean Sea level variability is a complex combination of a wide range of spatial and temporal scales. However, this paper gives an improved estimation of sea level statistics (rms, annual, semiannual cycle). Moreover, the longer period (1993–1999) and the merging of T/P and ERS-1/2 altimeter data allows us to observe with a good accuracy the major changes that occurred in the Mediterranean Sea and, in particular, at basin and sub-basin scales. First, important interannual signals were found in the Ionian basin where the cyclonic circulation has clearly intensified since 1997. In the Levantine basin, although the Ierapetra eddy exhibits a clear seasonal cycle, it is not always present during our period of observation.These interannual changes seem to be correlated with the variability of the Mid-Mediterranean Jet, which produces strong meanders. A new view of the circulation in the south of the basin is indeed suggested by considering that the eddies observed in the Mersa-Matruh and Shikmona areas represent meanders of the Mid-Mediterranean Jet rather than permanent structures as commonly described. Secondly, the seasonal cycle of the Alboran gyres is confirmed. Moreover, these gyres and the Ierapetra eddy constitute the most intense signals of the Mediterranean Sea variability. Finally, this descriptive study illustrates the need to continue monitoring the surface circulation in order to better understand the dynamics of the Mediterranean Sea. [Copyright &y& Elsevier]

There is growing evidence that the on-going ocean acidification of the Mediterranean Sea could be favoured by its active overturning circulation. The areas of dense water formation are, indeed, preferential sites for atmospheric carbon dioxide absorption and through them the ocean acidification process can quickly propagate into the deep layers. In this study we estimated the concentration of anthropogenic CO 2 (C ant ) in the dense water formation areas of the middle and southern Adriatic Sea. Using the composite tracer TrOCA (Tracer combining Oxygen, inorganic Carbon, and total Alkalinity) and carbonate chemistry data collected throughout March 2013, our results revealed that a massive amount of C ant has invaded all the identified water masses. High C ant concentration was detected at the bottom layer of the Pomo Pit (middle Adriatic, 96.8±9.7 µmol kg −1 ) and Southern Adriatic Pit (SAP, 85.2±9.4 µmol kg −1 ), associated respectively with the presence of North Adriatic Dense Water (NAdDW) and Adriatic Dense Water (AdDW). This anthropogenic contamination was clearly linked to the dense water formation events, which govern strong CO 2 flux from the atmosphere to the sea and the sinking of dense, CO 2 -rich surface waters to the deep sea. However, a very high C ant level (94.5±12.5 µmol kg −1 ) was also estimated at the intermediate layer, as a consequence of a recent vertical mixing that determined the physical and biogeochemical modification of the water of Levantine origin (i.e. Modified Levantine Intermediate Water, MLIW) and favoured the atmospheric CO 2 intrusion. The penetration of C ant in the Adriatic Sea determined a significant pH reduction since the pre-industrial era (– 0.139±0.019 pH units on average). This estimation was very similar to the global Mediterranean Sea acidification, but it was again more pronounced at the bottom of the Pomo Pit, within the layer occupied by NAdDW (– 0.157±0.018 pH units), and at the intermediate layer of the recently formed MLIW (– 0.143±0.020 pH units). Our results indicate that the Adriatic Sea could potentially be one of the Mediterranean regions most affected by the ocean acidification and also demonstrate its active role in sequestering and storing C ant . [ABSTRACT FROM AUTHOR]

The main objective of the LAgrangian Transport EXperiment (LATEX) project was to study the influence of coastal mesoscale and submesoscale physical processes on circulation dynamics, cross-shelf exchanges, and biogeochemistry in the western continental shelf of the Gulf of Lion, Northwestern Mediterranean Sea. LATEX was a five-year multidisciplinary project based on the combined analysis of numerical model simulations and multi-platform field experiments. The model component included a ten-year realistic 3D numerical simulation, with a 1 km horizontal resolution over the gulf, nested in a coarser 3 km resolution model. The in situ component involved four cruises, including a large-scale multidisciplinary campaign with two research vessels in 2010. This review concentrates on the physics results of LATEX, addressing three main subjects: (1) the investigation of the mesoscale to submesoscale processes. The eddies are elliptic, baroclinic, and anticyclonic; the strong thermal and saline front is density compensated. Their generation processes are studied; (2) the development of sampling strategies for their direct observations. LATEX has implemented an adaptive strategy Lagrangian tool, with a reference software available on the web, to perform offshore campaigns in a Lagrangian framework; (3) the quantification of horizontal mixing and cross-shelf exchanges. Lateral diffusivity coefficients, calculated in various ways including a novel technique, are in the range classically encountered for their associated scales. Cross-shelf fluxes have been calculated, after retrieving the near-inertial oscillation contribution. Further perspectives are discussed, especially for the ongoing challenge of studying submesoscale features remotely and from in situ data. [ABSTRACT FROM AUTHOR]

Changes in surface heat fluxes affect several climate processes controlling the Mediterranean climate. These include the winter formation of deep waters, which is the primary driver of the Mediterranean Sea overturning circulation. Previous studies that characterize the spatial and temporal variability of surface heat flux anomalies over the basin reveal the existence of two statistically dominant patterns of variability: a monopole of uniform sign and an east-west dipole of opposite signs. In this work, we use the 12 regional climate model ensemble from the EU-FP6 ENSEMBLES project to diagnose the large-scale atmospheric processes that control the variability of heat fluxes over the Mediterranean Sea from interannual to decadal timescales (here defined as timescales > 6 year). Our findings suggest that while the monopole structure captures variability in the winter-to-winter domain-average net heat flux, the dipole pattern tracks changes in the Mediterranean climate that are connected to the East Atlantic/Western Russia (EA/WR) atmospheric teleconnection pattern. Furthermore, while the monopole exhibits significant differences in the spatial structure across the multi-model ensemble, the dipole pattern is very robust and more clearly identifiable in the anomaly maps of individual years. A heat budget analysis of the dipole pattern reveals that changes in winds associated with the EA/WR pattern exert dominant control through both a direct effect on the latent heat flux (i.e., wind speed) and an indirect effect through specific humidity (e.g., wind advection). A simple reconstruction of the heat flux variability over the deep-water formation regions of the Gulf of Lion and the Aegean Sea reveals that the combination of the monopole and dipole time series explains over 90 % of the heat flux variance in these regions. Given the important role that surface heat flux anomalies play in deep-water formation and the regional climate, improving our knowledge on the dynamics controlling the leading modes of heat flux variability may enhance our predictability of the climate of the Mediterranean area. [ABSTRACT FROM AUTHOR]

The use of high resolution atmosphere-ocean coupled regional climate models to study possible future climate changes in the Mediterranean Sea requires an accurate simulation of the atmospheric component of the water budget (i.e., evaporation, precipitation and runoff). A specific configuration of the version 3.1 of the weather research and forecasting (WRF) regional climate model was shown to systematically overestimate the Mediterranean Sea water budget mainly due to an excess of evaporation (~1,450 mm yr) compared with observed estimations (~1,150 mm yr). In this article, a 70-member multi-physics ensemble is used to try to understand the relative importance of various sub-grid scale processes in the Mediterranean Sea water budget and to evaluate its representation by comparing simulated results with observed-based estimates. The physics ensemble was constructed by performing 70 1-year long simulations using version 3.3 of the WRF model by combining six cumulus, four surface/planetary boundary layer and three radiation schemes. Results show that evaporation variability across the multi-physics ensemble (∼10 % of the mean evaporation) is dominated by the choice of the surface layer scheme that explains more than ∼70 % of the total variance and that the overestimation of evaporation in WRF simulations is generally related with an overestimation of surface exchange coefficients due to too large values of the surface roughness parameter and/or the simulation of too unstable surface conditions. Although the influence of radiation schemes on evaporation variability is small (∼13 % of the total variance), radiation schemes strongly influence exchange coefficients and vertical humidity gradients near the surface due to modifications of temperature lapse rates. The precipitation variability across the physics ensemble (∼35 % of the mean precipitation) is dominated by the choice of both cumulus (∼55 % of the total variance) and planetary boundary layer (∼32 % of the total variance) schemes with a strong regional dependence. Most members of the ensemble underestimate total precipitation amounts with biases as large as 250 mm yr over the whole Mediterranean Sea compared with ERA Interim reanalysis mainly due to an underestimation of the number of wet days. The larger number of dry days in simulations is associated with a deficit in the activation of cumulus schemes. Both radiation and planetary boundary layer schemes influence precipitation through modifications on the available water vapor in the boundary layer generally tied with changes in evaporation. [ABSTRACT FROM AUTHOR]

The sensitivity of the dynamics of the Mediterranean Sea to atmospheric pressure and free surface elevation formulation using NEMO (Nucleus for European Modelling of the Ocean) was evaluated. Four different experiments were carried out in the Mediterranean Sea using filtered or explicit free surface numerical schemes and accounting for the effect of atmospheric pressure in addition to wind and buoyancy fluxes. Model results were evaluated by coherency and power spectrum analysis with tide gauge data. We found that atmospheric pressure plays an important role for periods shorter than 100 days. The free surface formulation is important to obtain the correct ocean response for periods shorter than 30 days. At frequencies higher than 15 days-1 the Mediterranean basin's response to atmospheric pressure was not coherent and the performance of the model strongly depended on the specific area considered. A large-amplitude seasonal oscillation observed in the experiments using a filtered free surface was not evident in the corresponding explicit free surface formulation case, which was due to a phase shift between mass fluxes in the Gibraltar Strait and at the surface. The configuration with time splitting and atmospheric pressure always performed best; the differences were enhanced at very high frequencies. [ABSTRACT FROM AUTHOR]

The first high-resolution time series of pre- and post-bomb radiocarbon measurements is reported for surface waters in the western Mediterranean Sea. The Δ14C record was obtained from the aragonite skeleton of Cladocora caespitosa using a 50-yr-old corallite collected in the Ligurian Sea in 1998. Laser-ablation ICP measurements of trace elements (Li/Mg and Sr/Ca) show a strong seasonal variability, enabling the chronology of the Δ14C record to be determined at annual timescales. The mean Δ14C of pre-bomb surface water is -56 ± 3‹, corresponding to a reservoir age of 262 ± 29 yr. The postbomb maximum occurs in 1972 with a Δ14C value of 90‹, significantly lower than the peak of 150‹ observed in the North Atlantic. The dilution of the peak-amplitude of Δ14C in western Mediterranean surface waters is attributed to mixing of North Atlantic Central Water inflow with relatively depleted underlying Intermediate Mediterranean and Levantine Intermediate waters. Intensification of this mixing is observed in 1963-1964, consistent with the change in atmospheric circulation from a positive to negative NAO phase (1960-1967). The post-peak Δ14C variability is relatively limited, reflecting mainly local vertical mixing forced by wind stress. [ABSTRACT FROM AUTHOR]

The European summer 2003 presents a rare opportunity to investigate dynamical interactions in the otherwise variable European climate. Not only did air temperature show a distinct signal, but the Mediterranean sea surface temperature (SST) was also exceptionally warm. The traditional view of the role of the Mediterranean Sea in the climate system highlights the influence of the atmospheric circulation on the Mediterranean Sea. The question of whether the Mediterranean Sea feeds back on the atmospheric dynamics is of central importance. The case of the extremely anomalous summer 2003 allows for investigating the issue under realistic boundary conditions. The present study takes advantage of a newly developed regional coupled atmosphere-ocean model for this purpose. Experiments with prescribed historical versus climatological SST suggest that the local atmospheric circulation is not strongly sensitive to the state of the Mediterranean Sea, but its influence on the moisture balance and its role in the regional hydrological cycle is substantial. Warmer Mediterranean SSTs lead to enhanced evaporation and moisture transport in the atmosphere. Results of regional coupled simulations with different ocean initial conditions imply that because of the strong stratification of the surface waters in summer, the response time of the upper layers of the Mediterranean Sea to atmospheric forcing is rather short. It can be concluded that the role of the Mediterranean Sea in the European summer climate is mostly passive. In winter, however, since the upper layers of the Mediterranean Sea are well mixed, the memory of the Mediterranean SSTs stretches over longer time scales, which implies a potential for actively governing regional climate characteristics to some extent. [ABSTRACT FROM AUTHOR]

Atmospheric circulation patterns that are conducive to extreme ocean heat loss are investigated at four sites of special interest in the Mediterranean Sea. The Gulf of Lions, the South Adriatic Sea, the Cretan Sea, and the Levantine Sea are areas where anomalously high winter heat loss may lead to deep- or intermediate-water formation. At each of the above sites, the atmospheric circulation during such events is derived by averaging the sea level pressure (SLP) fields during the lower decile of the wintertime series of the net heat exchange. A relatively simple SLP pattern dominated by an anticyclone over northwestern Europe with a weaker cyclone to the southeast is found to be associated with strong heat loss in the selected sites with minor variations in pattern structure depending on the site. The SLP composite pattern reflects the combined effect of different atmospheric modes of variability and the authors consider the impacts on heat loss of a number of these modes (North Atlantic Oscillation, east Atlantic pattern, east Atlantic-west Russia pattern, and Scandinavian pattern), together with the North Sea-Caspian pattern and the Mediterranean index. The extremes in heat loss are strongly connected with the intensity and the positions of the poles of these patterns that modulate, through the necessary SLP gradient and associated northerlies, the transfer of cold and dry air over the areas of dense-water formation. Analysis of air-sea temperature difference, specific humidity, and evaporation anomalies indicates that the extremes of the net heat fluxes are primarily due to the latent and sensible heat flux components. [ABSTRACT FROM AUTHOR]

A phenomenon characterized by a tongue of low pressure extending northward from the southern Red Sea [Red Sea Trough (RST)] toward the eastern Mediterranean Sea (EM) is analyzed. In general, the RST is associated with hot and dry weather, resulting from east-southeasterly flows in the lower troposphere. In some cases, the RST is found to be accompanied by an upper-tropospheric trough extending from the north over the EM. Such conditions are associated with unstable stratification, favoring the development of mesoscale convective systems. This kind of RST has been defined as an 'active' RST (ARST). The ARST phenomenon represents a serious threat to human society in the northeastern Africa-southeastern Mediterranean region, being in some cases associated with devastating floods. In this study, a conceptual model of the ARST phenomenon is discussed, and then an algorithm for the identification of ARST events is presented. The identification algorithm has been applied to a multiyear NCEP-NCAR reanalysis data archive for both RST and ARST events. From the results of a composite analysis of several different atmospheric flow parameters associated with ARST events, the key features associated with ARST events are identified. The results from the analysis of the composite patterns support the suggestion that high amounts of moisture transported from tropical Africa in the form of an atmospheric river to the Red Sea-EM play a key role in determining the intensity of the ARST events. [ABSTRACT FROM AUTHOR]

Mediterranean basins are known for their susceptibility to water stress conditions resulting from a reduction in winter-season precipitation. This region is also prone to the effects of the North Atlantic Oscillation (NAO), a large-scale climatic pattern associated with a displacement of air mass between the arctic and the subtropical Atlantic. Even though previous studies have demonstrated the impact of the NAO on winter climate conditions in Europe and Northern Africa, it is still unclear to what extent the NAO is related to hydroclimatic patterns in Mediterranean areas and whether it can explain its recent drought history. To this end, this study investigates the interdependence between the NAO and winter precipitation, river flow and temperature in two Mediterranean regions: Southern Italy and Nile Delta (Egypt). The outcomes show the presence of significant connections between the NAO, winter rainfall and river discharge. [ABSTRACT FROM AUTHOR]

We describe the implementation of an operational high resolution wind and wave forecasting system in the Mediterranean Sea, and then on a limited area centred on the south-east part of Italy, covering parts of the Adriatic and the Ionian seas. We analyse the performance at the two different resolutions during the first four months of operation, using the wind and wave data provided by the QuikSCAT scatterometer, and the Jason and Envisat altimeters. Useful accurate forecasts are found up to 72 h range, the maximum operational one. As expected, we find that the limited area models outperform both the wind and wave global or larger scale model results. However, we still find an appreciable underestimate by the models for surface wind speed and hence wave height, often concentrated on specific events. [ABSTRACT FROM AUTHOR]

The sensitivity of the atmospheric circulation to the warm Mediterranean sea surface temperature (SST) anomalies observed during the summer of 2003 (July and August) is studied using the European Centre for Medium-Range Weather Forecasts (ECMWF) model. A control integration imposes climatological Mediterranean SSTs as a lower boundary condition. The first sensitivity experiment uniformly increases these Mediterranean SSTs by 2 K, the approximate mean observed in the 2003 summer season. A second experiment then investigates the additional impact of the SST distribution by imposing the observed SST summer anomaly. The response of the atmospheric circulation in the European area shows some resemblance to the observed anomaly. The weakness of this response suggests, however, that the warm Mediterranean played a minor role, if any, in maintaining the anomalous atmospheric circulation as observed in the summer of 2003. Increasing SST in the Mediterranean locally leads to an increase in precipitation, particularly in the western Mediterranean. Furthermore, significantly increased Sahelian rainfall is simulated, deriving from enhanced evaporation in the Mediterranean Sea. In the ECMWF model the anomalously high moisture is advected by the climatological Harmattan and Etesian winds, where enhanced moisture flux convergence leads to more precipitation. The associated diabatic heating leads to a reduction of the African easterly jet strength. A similar Sahelian response has been previously documented using a different atmospheric model, increasing confidence in the robustness of the result. Finally, the results are discussed in the context of the seasonal predictability of European and African climate. [ABSTRACT FROM AUTHOR]

The effects of wave-current interactions on shelf ocean forecasts is investigated in the framework of the MFSTEP (Mediterranean Forecasting System Project Towards Enviromental Predictions) project. A one way sequential coupling approach is adopted to link the wave model (WAM) to the circulation model (SYMPHONIE). The coupling of waves and currents has been done considering four main processes: wave refraction due to currents, surface wind drag and bottom drag modifications due to waves, and the wave induced mass flux. The coupled modelling system is implemented in the southern Catalan shelf (NW Mediterranean), a region with characteristics similar to most of the Mediterranean shelves. The sensitivity experiments are run in a typical operational configuration. The wave refraction by currents seems to be not very relevant in a microtidal context such as the western Mediterranean. The main effect of waves on current forecasts is through the modification of the wind drag. The Stokes drift also plays a significant role due to its spatial and temporal characteristics. Finally, the enhanced bottom friction is just noticeable in the inner shelf. [ABSTRACT FROM AUTHOR]

Examines the inter-annual response of Mediterranean basin to low-frequency inter-annual variability in atmospheric circulation. Incorporation of a realistic scheme for air-sea interaction; Characteristics of heat flux winter anomalies; Processes associated with oceanic general circulation.