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  • 1
    Electronic Resource
    Electronic Resource
    Absence of confinement in the absence of vortices (1999)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 40 (1999), S. 4677-4687 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: We consider the Wilson loop expectation in SU(2) lattice gauge theory in the presence of constraints. The constraints eliminate gauge field configurations, which, in physical terms, allow the presence of thick center vortices linking with the loop. We prove that, for dimension d≥3, the so-constrained Wilson loop follows perimeter law, i.e., nonconfining behavior, at weak coupling (low temperature). © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.532997
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  • 2
    Electronic Resource
    Electronic Resource
    pH-dependent activation of the alternative transcriptional factor σB in Bacillus subtilis (1998)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 165 (1998), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The expression of the sigB gene of Bacillus subtilis was analysed in response to a mild acid shock. This gene is subject to σB-dependent regulation. It has been found that the expression of sigB is induced as part of the acid-tolerant response. In that respect sigB is similar to the previously described gene gsiB which is also a member of the σB regulon. Through this induction, the σB regulon provides protection against acid shock. Besides its protective role against acid shock, no other general function could be directly associated with the σB regulon. An acidification of the cytoplasmic environment induces synthesis of general stress proteins in B. subtilis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1998.tb13164.x
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  • 3
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    The role of wind stress in the Arctic and North Atlantic freshwater covariability (2018)
    In:  EPIC3FAMOS Workshop, Bergen, Norway, 2018-10-23-2018-10-26
    Details
    Publication Date: 2018-11-01
    Description: Observations from recent decades show significant salinity anomalies in the Arctic and the subpolar North Atlantic oceans. The evolution of their freshwater budgets has been the focus of many studies, most of which suggest a link between them. However, the nature and the significance of this link is still disputed, as are the driving forces behind it. Our aim was to perform a series of numerical simulations of the freshwater system of the Arctic and the subpolar North Atlantic oceans and to assess the role of wind stress in shaping it. For this we used the Max Planck Institute Earth System Model and ran model experiments in a partially coupled configuration applying the so called Modini-method with prescribed wind forcing. We constructed idealized scenarios of wind stress forcing associated with large-scale patterns of observed atmospheric variability. We present our results from scenarios representing prolonged positive or negative states of the AO/NAO. We also analyze the response to a sudden change from one state to another with particular focus on the Arctic and the North Atlantic freshwater reservoirs and the fluxes between them. This enables us to simulate the high freshwater content observed in the Beaufort Gyre concurrent with an unusually persistent anticyclonic wind pattern in the Arctic in recent years, and to study the effect of large-scale circulation shifts on Arctic freshwater export and thus salinity anomalies in the subpolar North Atlantic Ocean.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 4
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    Arctic Ocean Response to Greenland Sea Wind Anomalies in a Suite of Model Simulations (2019)
    In:  EPIC3Journal of Geophysical Research: Oceans, 124(8), pp. 6286-6322
    Details
    Publication Date: 2020-05-18
    Description: Abstract Multimodel Arctic Ocean "climate response function" experiments are analyzed in order to explore the effects of anomalous wind forcing over the Greenland Sea (GS) on poleward ocean heat transport, Atlantic Water (AW) pathways, and the extent of Arctic sea ice. Particular emphasis is placed on the sensitivity of the AW circulation to anomalously strong or weak GS winds in relation to natural variability, the latter manifested as part of the North Atlantic Oscillation. We find that anomalously strong (weak) GS wind forcing, comparable in strength to a strong positive (negative) North Atlantic Oscillation index, results in an intensification (weakening) of the poleward AW flow, extending from south of the North Atlantic Subpolar Gyre, through the Nordic Seas, and all the way into the Canadian Basin. Reconstructions made utilizing the calculated climate response functions explain ~50% of the simulated AW flow variance; this is the proportion of variability that can be explained by GS wind forcing. In the Barents and Kara Seas, there is a clear relationship between the wind-driven anomalous AW inflow and the sea ice extent. Most of the anomalous AW heat is lost to the atmosphere, and loss of sea ice in the Barents Sea results in even more heat loss to the atmosphere, and thus effective ocean cooling. Release of passive tracers in a subset of the suite of models reveals differences in circulation patterns and shows that the flow of AW in the Arctic Ocean is highly dependent on the wind stress in the Nordic Seas.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    Wind Feedback Mediated by Sea Ice in the Nordic Seas (2020)
    In:  EPIC3Journal of Climate, 33(15), pp. 6621-6632
    Details
    Publication Date: 2020-07-08
    Description: Air-sea interactions play a critical role in the climate system. This study investigates wind-induced changes in the ocean surface temperature and sea ice cover feeding back onto the atmospheric circulation. This interaction was modeled in the Nordic seas, using a partial coupling method to constrain the ocean with prescribed wind forcing in an otherwise fully coupled Earth system model. This enabled the evaluation of not only the direct oceanic, but also the indirect atmospheric response to idealized forcing scenarios of perturbed winds over the Nordic seas. The results show that an anticyclonic wind anomaly forcing leads to significant surface cooling in the Greenland Sea mostly due to anomalous drift of sea ice. During winter, the cooling reduces the net surface heat flux to the atmosphere and increases sea level pressure. The pressure gradients result in anomalous geostrophic southerly winds, which locally are comparable both in direction and in velocity to the prescribed forcing anomalies, suggesting a positive feedback.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    RACE TP 2.1: Arctic Circulation as part of the North Atlantic current system (2016)
    In:  EPIC3RACE Abschlussseminar, Bremen, DE
    Details
    Publication Date: 2017-12-15
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
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    Drivers of freshwater distribution in the Arctic and Atlantic oceans (2016)
    In:  EPIC3FAMOS Workshop, Woods Hole, USA, 2016-11-01-2016-11-04
    Details
    Publication Date: 2018-07-23
    Description: Oceanic circulation plays an important role in setting the climate of the Arctic and the Northern Atlantic regions. Currents conveying large volumes of water masses at various depths transport heat and salt to great distances, forming a global circulation system. In the Atlantic, the Meridional Overturning Circulation (MOC) is driven by exchanges of heat, freshwater and momentum with the atmosphere. Previous modeling studies suggest that the stability of the MOC is sensitive to different climate scenarios due to the sensitivity of the deepwater formation, a crucial component of the circulation to perturbations of freshwater content. Global climate models predict significant temperature rise in the future with larger trends at higher latitudes, and an enhanced hydrological cycle. Both of these trends act against the MOC, decreasing its strength by reducing meridional air temperature differences and freshening of ocean waters in key high latitude areas. The observed increase of the strength of the North Atlantic Oscillation (NAO) in recent decades, a trend that is predicted by many climate models to persist in the future, however, acts as a driver of the MOC. This duel of the evolution of fresh water fluxes and the development of the NAO is most likely going to define the strength of the MOC in the future. We examine the effects of different NAO scenarios using the Modini-system, a partially coupled spin-up that allows prescription of wind stresses for the ocean in the otherwise fully coupled Earth System Model of the Max Planck Institute. In our work we describe the processes affecting the circulation in more detail. We present our first results by investigating the role different wind stress patterns play in shaping fresh water reservoirs and exchanges between different subregions of the Arctic and the Atlantic Ocean.
    Repository Name: EPIC Alfred Wegener Institut
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  • 8
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    Wind forcing of the Arctic and North Atlantic freshwater system (2017)
    In:  EPIC3YOUMARES 8, Kiel, Germany, 2017-09-13-2017-09-15
    Details
    Publication Date: 2018-07-23
    Description: Oceanic processes in the Arctic and in the North Atlantic that play a key role in the global ocean circulation are often sensitive to density stratification of water, which is greatly shaped by salinity, or in another measure, by freshwater content. The freshwater budgets of these oceans are connected by currents that convey large volumes of water of different characteristics between one another. However, these budgets show spatial and temporal variations, and the fluxes between them cannot be considered constant either. The freshwater system of the Arctic linked to the North Atlantic is dynamic with changes and anomalies on different time scales, and the changes of this joint system seem to be in correlation with the evolution of atmospheric forcing patterns. Previous studies suggest the importance of wind stress forcing over key regions such as the Beaufort Sea or the Greenland Sea in influencing the distribution of freshwater. In this study we examine the sensitivity of freshwater distribution and fluxes between the Arctic and the North Atlantic oceans to wind stress forcing through numerical experiments. The tool for this is the Modini-system, a partial coupling technique that allows flexible experiments with prescribed wind stress fields for the ocean in the otherwise fully coupled Earth System Model of the Max Planck Institute. In this work we present the first results in investigating the role of atmospheric forcing in shaping freshwater reservoirs and exchanges between different oceanic subregions by comparing our model results using external wind stress forcing with the Modini-system, and fully coupled runs.
    Repository Name: EPIC Alfred Wegener Institut
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  • 9
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    Wind stress forcing in the Arctic and North Atlantic oceans (2018)
    In:  EPIC3POLAR2018 Open Science Conference, Davos, Switzerland, 2018-06-19-2018-06-23
    Details
    Publication Date: 2018-07-23
    Description: One of the key processes responsible for driving the circulation of ocean waters is the wind stress. This important air-sea interaction stands for the imparting of atmospheric momentum to the ocean. The prevailing wind patterns largely influence the velocity in the top Ekman layer in the ocean, sustaining the observed system of surface currents. Given the internal variability of the wind climate, these surface currents are subject to anomalies in space and time that can have large scale effects on oceanic processes. This is particularly true in the Arctic and the subpolar North Atlantic oceans that play a key role in the global ocean circulation, and are influenced by variations of wind stress forcing associated with large scale atmospheric modes in these regions. In this study we examine the sensitivity of surface currents, ice cover, freshwater and heat content in these ocean basins to wind stress forcing through numerical experiments. The tool for this is the Modini-system, a partial coupling technique that allows flexible experiments with prescribed wind stress fields for the ocean in the otherwise fully coupled Earth System Model of the Max Planck Institute. In this work we present our results investigating the role of wind stress forcing in shaping the distribution and exchanges of state variables in and between the Arctic and North Atlantic oceans by comparing our model results using external wind stress forcing with the Modini-system, and fully coupled runs.
    Repository Name: EPIC Alfred Wegener Institut
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  • 10
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    Climate response functions of the joint freshwater budget of the Arctic and North Atlantic oceans to changes in external wind forcing in an otherwise fully coupled earth system model (2017)
    In:  EPIC3FAMOS Workshop, Woods Hole, USA, 2017-10-24-2017-10-27
    Details
    Publication Date: 2018-07-23
    Description: Ocean currents conveying large volumes of water can transport heat to great distances, through which they influence the climate. This is particularly true for the Arctic and the North Atlantic, the regions where water circulation has a significant impact on the atmosphere as well as on key oceanic processes. These processes are often sensitive to density stratification of ocean water, which is greatly shaped by salinity, or in another measure, by freshwater storage. Freshwater in the oceans is thus of particular importance. Being connected by a network of currents, the Arctic and North Atlantic oceans exchange a large volume of water of different characteristics. As a consequence, their freshwater budgets are also connected. However, these budgets show spatial and temporal variations, and the fluxes between them cannot be considered constant either. The freshwater system of the Arctic linked to the North Atlantic is dynamic with changes and anomalies on different time scales, and the changes of this joint system seem to follow the evolution of atmospheric forcing patterns. Previous modeling results suggest the importance of wind stress forcing over key regions such as the Beaufort Sea or the Greenland Sea in influencing the distribution of freshwater. In this study we examine the reaction of this linked freshwater system to changes in wind stress forcing through numerical experiments using the Modini-system, a partial coupling technique that allows flexible experiments with prescribed wind stress fields for the ocean in the otherwise fully coupled Earth System Model of the Max Planck Institute. The aim of this work is to investigate the role of atmospheric forcing in shaping freshwater reservoirs and exchanges between different subregions of the Arctic and North Atlantic oceans by calculating and analyzing climate response functions to changes in wind forcing over key regions.
    Repository Name: EPIC Alfred Wegener Institut
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