1,721,159 research outputs found
Sea level forcing in the Mediterranean Sea between 1960 and 2000
No full textSea level trends and inter-annual variability in the Mediterranean Sea for the period 1960–2000 is explored by comparing observations from tide gauges with sea level hindcasts from a barotropic 2D circulation model, and two full primitive equation 3D ocean circulation models, a regional one and the Mediterranean component of a global one,. In the 2D model, 50% of the sea level variance was found to result from the wind and atmospheric pressure forcing. In the 3D models, 20% of the sea level variance was explained by the steric effects. The sea level residuals at the tide gauges locations, calculated by subtraction of the 2D model output from the sea level observations are significantly correlated (r = 0.4) with the steric signals from the 3D models. After the removal of the atmospheric and the steric contributions the tide-gauge sea level records indicate a period where sea level was stable (1960–1975) and a period where sea level was rising (1975–2000) with rates in the range 1.1–1.8 mm/yr. A part of the residual trend can be explained by the contribution of local land movements (0.3 mm/yr) while its major part indicates a global signal, probably mass addition, appearing after 1975.<br/
Impacts of atmospheric modes of variability on Mediterranean Sea surface heat exchange
No full textThe impacts of variations in the state of the first four modes of atmospheric variability in the North Atlantic/Europe region on air-sea heat exchange in the Mediterranean Sea are considered. Observation-based indices of these modes from the NOAA Climate Prediction Centre are used together with two reanalysis (NCEP/NCAR and ARPERA) surface flux data sets for the period 1958–2006 to determine their relative influence on the mean heat budget of the full Mediterranean basin and the eastern and western subbasins. The modes considered are the North Atlantic Oscillation (NAO), East Atlantic pattern (EA), Scandinavian pattern (SCAN), and East Atlantic/West Russian pattern (EA/WR). Similar results are obtained with both NCEP/NCAR and ARPERA. In each case, winter anomalies dominate the annual mean heat budget and the leading mode, the NAO, has a surprisingly small impact on the full basin winter mean heat budget, <5 Wm?2. In contrast, the EA mode has a major effect, of order 25 Wm?2, with similar impacts on both the eastern and western Mediterranean. The SCAN mode has the weakest influence of those considered. The EA/WR mode plays a significant role but, in contrast to the EA mode, it generates a dipole in the heat exchange with an approximately equal and opposite signal of about 15 Wm?2 on the eastern and western subbasins. A particularly strong impact in the Aegean Sea is observed for the EA/WR mode and this is discussed in the context of episodic deep water formation in this region
Mechanisms controlling the thermohaline circulation pattern variability in the Aegean–Levantine region. A hindcast simulation (1960–2000) with an eddy resolving model
No full textA hindcast simulation in the Aegean–Levantine basins for the years 1960–2000 is performed, using an eddy resolving ocean model (1°/30). The model incorporates a 6-h atmospheric forcing provided by the ARPERA and captures the observed variability of the 40-years. The Eastern Mediterranean Transient (EMT) is the most prominent climatic event of the period. We investigate the impact of the atmospheric versus lateral forcing on the buoyancy content of the Aegean–Levantine basins. During the pre-EMT period, the basins’ buoyancy content is lowered by surface fluxes by about 1.5×10?8 m2 s?3 in the Aegean Sea, mostly related to surface heat loss, and lateral fluxes by about 0.9×10?8 m2 s?3, mostly related to salt flux, with the Levantine changes leading those of the Aegean. Furthermore, while long-term trends of surface and lateral inputs are preconditioning the changes in the Aegean stratification, it is the extreme heat loss pulses, related to the variability of the wind field that is controlling the formation processes by abruptly lowering the buoyancy content. Those events are possibly linked to an eastern Mediterranean bimodal atmospheric oscillation, with the anomalous surface heat fluxes shifting from the Levantine in the 1960s to the Aegean in the 1990s. The central Aegean due to its topography and thermohaline properties trigger events of excessive formation and producing the Aegean’s densest waters. During the EMT winters the central Aegean lower layers contain very dense waters, with ?? larger than 29.3 kg m?3. These waters form the core of the water mass outflowing in the Eastern Mediterranean, after being mixed with ambient waters along their southward flow. The outflowing layer is characterized by density of 29.21 kg m?3. The deepest parts of the NW Levantine is initially filled with the new water mass, which later spreads to the SE parts of the basin, flowing over the Eastern Mediterranean Ridge
Sea level variability in the Mediterranean Sea during the 1990s on the basis to two 2d and one 3d model
No full textThe sea level rise in the 1990s at the Mediterranean Sea as evidenced by satellite altimetry is studied with the aid of ocean models. Two barotropic two dimensional (2d) models and one three dimensional (3d) model are used. Both 2d models indicate that the contribution of direct atmospheric forcing causes localised trends of up to 2 mm/yr. The 3d model successfully describes the evolution in temperature of the upper and intermediate waters. However the salinity changes are not well described. The steric contribution of sea level rise during this period is in places in excess of 10 mm/yr. Notably oceanic circulation is also found to contribute to sea level trends by up to ? 3 mm/yr. Thus the observed sea level changes in the 1990s are better understood. The exceptional nature of the sea level behaviour in 1990s, especially in the eastern basin, when compared with previous decades is confirmed on the basis of both the 2d and the 3d models
Large-Scale Atmospheric Circulation Favoring Deep- and Intermediate-Water Formation in the Mediterranean Sea
No full textAtmospheric 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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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