1,721,043 research outputs found
Reconciling the north–south density difference scaling for the Meridional Overturning Circulation strength with geostrophy
No full textSince the formulation of the Stommel two-box model for the meridional overturning circulation (MOC), various theoretical and conceptual models for the MOC emerged based on scaling the MOC strength with the north south density difference. At the same time the MOC should obey geostrophic balance with an east-west density difference. Scaling with the north south density gradient seems to violate the common assumption of geostrophic balance for the large-scale circulation, which implies that the pressure gradient is orthogonal to the flow. In this brief report, we report on the results of a series of numerical simulations in an idealized ocean basin (with a zonally periodic channel at its southern end). The simulations performed with different surface forcing conditions indicate that the meridional and zonal density gradients, important for the MOC strength, are in fact related to each other through the stratification located at the northern end of the periodic channel. The results suggest that the water properties at the northern end of the periodic channel play a crucial role in setting the MOC strength, possibly explaining the sensitivity of climate models to the conditions in this area
Sensitivity of basin-wide meridional overturning in an idealized Atlantic-Southern Ocean geometry
No full textAtlantic salinity budget in response to Northern and Southern Hemisphere ice sheet discharge
No full textThe impact of an idealised scenario of future mass release of major ice sheets on the Atlantic ocean is studied. A freshwater forcing is applied to the ocean surface in a coupled climate model forced in accordance with a high-end future climate projection for mass loss from the Greenland and Antarctic ice-sheet, together with the RCP8.5 emission scenario. The added freshwater dilutes the entire ocean by increasing total volume, but changes in freshwater budget are non-linear in time, especially in the Atlantic Ocean. In the Atlantic the initial dilution mainly comes from Greenland freshwater, but the increase in mass is counteracted by the mass flux across the boundaries of the Atlantic, with the outflow into the Southern Ocean becoming larger than the inflow through Bering Strait. Associated with this mass divergence, salt is exported to the Southern Ocean by the barotropic flow. Further freshening is associated with more freshwater import by the Atlantic Meridional Overturning Circulation across the southern boundary of the Atlantic. Also, the subtropical gyre exports salt and imports freshwater across the Atlantic’s southern boundary, especially when freshwater from the Antarctic Ice Sheet arrives at the boundary of the basin. It appears that the response to Northern Hemisphere (NH) sources (the Greenland Ice Sheet) and Southern Hemisphere (SH) sources (the Antarctic Ice Sheet) are opposite. In the case of NH-only freshwater forcing, sea surface height (SSH) increases in the Arctic, causing a reduction of the SSH gradient over the Bering Strait, and hence the barotropic throughflow across the Arctic–Atlantic basin reduces. In case of SH-only freshwater forcing, SSH increases in the Pacific, enhancing the barotropic throughflow in the Arctic–Atlantic. When both NH and SH freshwater forcings are present, the response in the Atlantic is dominated by NH forcing. Changes in overturning transport to either NH or SH forcing counteract the response to changes in barotropic transport. These changes are not due to volume transport but mainly due to salinity changes, in particular across the southern boundary of the Atlantic. Only when both SH and NH freshwater forcing are present changes in barotropic transport and overturning transport reinforce each other: the barotropic transport more strongly reacts to NH forcing, while the overturning transport reacts more strongly to SH forcing.</p
Sea level changes in the North Atlantic by solar forcing and internal variability
No full textSea level change due to variations in the thermohaline structure of the North Atlantic has been calculated using a coupled ocean–atmosphere model of intermediate complexity (ECBilt). Two 1000-year simulations are made, one using a constant solar forcing and one using an estimate of historic variations in solar activity. In the solar forced simulation sea level variations are a proxy for climate variations. Anomalies in sea surface temperature (SST) of the northern North Atlantic are generated by the solar radiation changes. These SST anomalies modulate the ocean thermohaline circulation (THC), affecting surface salinities in the northern North Atlantic which are subsequently advected to the deep ocean. The associated deep ocean geopotential thickness anomalies dominate sea level in the North Atlantic and are advected southwards with the overturning circulation. Sea level change in the solar forced simulation is primarily an indirect response to solar radiation changes, which modulate the THC. In the unforced run, changes in the THC affect sea level in a similar way. However, in this simulation THC variability is no longer generated by sea surface temperature variations but by sea surface salinity variations, resulting from internal climate dynamics. The present results will aid in analyses of reconstructed low-frequency sea-level variations based on proxy data
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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