1,720,996 research outputs found
Observing and modeling changes in the Atlantic MOC
No full textThe Atlantic Meridional Overturning Circulation (MOC) is defined, and our present understanding of MOC driving mechanisms is summarized. Evidence for the changing MOC is reviewed, covering recent developments in observing and modeling the MOC, and the climatic consequences of MOC variability. On a timescale of the next 5-10 years, further developments in MOC monitoring, modeling and prediction are both anticipated and recommended. In the context of what is presently known about the MOC, the evidence for a recent slowing trend is considered
How wind-forcing and air-sea heat exchange determine the meridional temperature gradient and stratification for the Antarctic Circumpolar Current
Full text linkMesoscale oceanic eddies have a profound effect on the meridional circulation in the Antarctic Circumpolar region. Previous studies have shown that eddies transport heat poleward to balance the heat lost by the ocean to the atmosphere in the waters around Antarctica and also transport eastward momentum downward at a rate comparable to the amount of momentum put into the water column by the wind stress. Using the poleward eddy heat fluxes to relate air-sea heat loss and wind stress, we find that the meridional temperature gradient in the circumpolar region is determined by the ratio of the air-sea heat loss to the zonal wind stress. Including a widely used parameterisation where poleward eddy heat fluxes are proportional to the mean meridional temperature gradient, we find that the slope of isotherms (or isopycnals) across the circumpolar zone is determined by the wind stress. Further assuming no cross-isopycnal mixing in the interior ocean, we find that the stratification in the deep ocean is determined by the ratio of air-sea heat loss to zonal wind stress squared. The poleward eddy heat fluxes also represent a southward eddy mass transport in the upper water column in density coordinates. The vertical gradient of this eddy mass transport is the meridional component of the eddy Stokes drift which is equal to the difference between the Lagrangian and Eulerian mean velocities in the circumpolar region. Because there can be no zonally averaged geostrophic Eulerian meridional velocity across the circumpolar region above the topography, this southward eddy Stokes drift provides a mechanism by which circumpolar deep water can flow southward across the circumpolar zone. Eddy heat fluxes, which are central to the mass, momentum, heat and energy balances in the circumpolar region, provide a catalyst for relating the roles of wind and buoyancy forcing in setting the overall circulation for the Southern Ocean
Comments on “Decadal Changes in the North Atlantic and Pacific Meridional Overturning Circulation and Heat Flux”
No full textIt is demonstrated that current level models, both with and without assimilation, generate too shallow an overturning in the North Atlantic (just like their predecessors) because they do not reproduce the descent of plumes of cold water from the Greenland and Norwegian Seas. Consequently, the prediction of decadal change from one such model reported by C. Wunsch and P. Heimbach is queried.<br/
Large-scale forcing of the European Slope Current and associated inflows to the North Sea
No full textDrifters drogued at 50?m in the European Slope Current at the Hebridean shelf break follow a wide range of pathways, indicating highly variable Atlantic inflow to the North Sea. Slope Current pathways, timescales and transports over 1988–2007 are further quantified in an eddy-resolving ocean model hindcast. Particle trajectories calculated with model currents indicate that Slope Current water is largely ''recruited'' from the eastern subpolar North Atlantic. Observations of absolute dynamic topography and climatological density support theoretical expectations that Slope Current transport is to first order associated with meridional density gradients in the eastern subpolar gyre, which support a geostrophic inflow towards the slope. In the model hindcast, Slope Current transport variability is dominated by abrupt 25–50?% reductions of these density gradients over 1996–1998. Concurrent changes in wind forcing, expressed in terms of density gradients, act in the same sense to reduce Slope Current transport. This indicates that coordinated regional changes of buoyancy and wind forcing acted together to reduce Slope Current transport during the 1990s. Particle trajectories further show that 10–40?% of Slope Current water is destined for the northern North Sea within 6 months of passing to the west of Scotland, with a clear decline in this Atlantic inflow over 1988–2007. The influence of variable Slope Current transport on the northern North Sea is also expressed in salinity, which declines through the hindcast period, and there is evidence for a similar freshening trend in observational records. A proxy for Atlantic inflow may be found in sea level records. Variability of Slope Current transport is implicit in mean sea level differences between Lerwick (Shetland) and Torshavn (Faeroes), in both tide gauge records and a longer model hindcast spanning 1958–2013. Potential impacts of this variability on North Sea biogeochemistry and ecosystems, via associated changes in seasonal stratification and nutrient fluxes, are discussed
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
Seasonal cycles of oceanic transports in the eastern subpolar North Atlantic
No full textThe variability of the Atlantic Meridional Overturning Circulation (AMOC) may play a role in sea surface temperature predictions on seasonal to decadal time scales. Therefore, AMOC seasonal cycles are a potential baseline for interpreting predictions. Here, we present estimates for the seasonal cycle of transports of volume, temperature, and freshwater associated with the upper limb of the AMOC in the eastern subpolar North Atlantic on the Extended Ellett Line hydrographic section between Scotland and Iceland. Due to weather, ship-based observations are primarily in summer. Recent glider observations during other seasons present an opportunity to investigate the seasonal variability in the upper layer of the AMOC. First, we document a new method to quality control and merge ship, float, and glider hydrographic observations. This method accounts for the different spatial sampling rates of the three platforms. The merged observations are used to compute seasonal cycles of volume, temperature, and freshwater transports in the Rockall Trough. These estimates are similar to the seasonal cycles in two eddy-resolving ocean models. Volume transport appears to be the primary factor modulating other Rockall Trough transports. Finally, we show that the weakest transports occur in summer, consistent with seasonal changes in the regional-scale wind stress curl. Although the seasonal cycle is weak compared to other variability in this region, the amplitude of the seasonal cycle in the Rockall Trough, roughly 0.5 to 1 Sv about a mean of 3.4 Sv, may account for up to 7 to 14% of the heat flux between Scotland and Greenland
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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