Atmospheric winter response to a projected future Antarctic sea-ice reduction: a dynamical analysis     

Jürgen Bader  Martin Flügge  Nils Gunnar Kvamstø  Michel D. S. Mesquita  Aiko Voigt 《Climate Dynamics》2013,40(11-12):2707-2718

Several studies have analysed the atmospheric response to sea-ice changes in the Arctic region, but only few have considered the Antarctic. Here, the atmospheric response to sea-ice variability in the Southern Hemisphere is investigated with the atmospheric general circulation model ECHAM5. The model is forced by the present and a projected future seasonal cycle of Antarctic sea ice. In September, the mean atmospheric response exhibits distinct similarities to the structure of the negative phase of the Southern Annular Mode, the leading mode of Southern Hemisphere variability. In the reduced Antarctic sea-ice integration, there is an equatorward shift of the Southern Hemisphere mid-latitude jet and the storm tracks. In contrast to a recent previous study, our findings indicate that a substantial impact of Southern Hemispheric future sea-ice reduction on the mid-latitude circulation cannot be ruled out.  相似文献   

CO2 equivalences for short-lived climate forcers     

Odette Deuber  Gunnar Luderer  Robert Sausen 《Climatic change》2014,122(4):651-664

With advancing climate change there is a growing need to include short-lived climate forcings in cost-efficient mitigation strategies to achieve international climate policy targets. Tools are required to compare the climate impact of perturbations with distinctively different atmospheric lifetimes and atmospheric properties. We present a generic approach for relating the climate effect of short-lived climate forcers (SLCF) to that of CO₂ emissions. We distinguish between three alternative types of metric-based factors that can be used to derive CO₂ equivalences for SLCF: based on forcing, activity and fossil fuel consumption. We derive numerical values for a wide range of parameter assumptions and apply the resulting generalised approach to the practical example of aviation-induced cloudiness. The evaluation of CO₂ equivalences for SLCF tends to be more sensitive to SLCF specific physical uncertainties and the normative choice of a discount rate than to the choice of a physical or economic metric approach. The ability of physical metrics to approximate economic-based metrics alters with changing atmospheric concentration levels and trends. Under reference conditions, physical CO₂ equivalences for SLCF provide sufficient proxies for economic ones. The latter, however, allow detailed insight into structural uncertainties. They provide CO₂ equivalences for SLCF in short term strategies in the face of failing climate policies, and a temporal evolution of CO₂ equivalences over time that is noticeably better in line with cost-efficient climate stabilisation.  相似文献   

Effects of virus infection on expression of cell cycle regulatory proteins in the unicellular marine algae Emiliania huxleyi     

LIU Jingwen  Gunnar Bratbak  ZHENG Tianling  Runar Thyrhaug 《海洋学报(英文版)》2011,30(4):89-95

The authors have investigated the biochemical events by which marine algal virus infection induces cell cycle arrest. The key G₂/M-phase regulatory proteins are analyzed by immunobloting in unicellular Emiliania huxleyi, suggesting that virus induced cell cycle arrest is related with virus''s effect on cyclins and cyclin dependent kinases. E. huxleyi virus (EhV) represses Cdc2/cyclinB complex activity by inhibiting the activity of Cdc2 kinase in a phosphorylation-related manner, blocking host cells G₂/M checkpoint. Dephosphorylated/inactive Cdc25C combined with up-regulation of Wee1 expression at early infect period appears to be important mechanisms by which EhV represses Cdc2/cyclinB complex activity that is required for entry into M phase. This study has allowed us to confirm that algal virus infection leads to selective activation or inhibition of certain cell-cycle factors, which may play a significant role in establishing a more efficient environment for viral gene expression and DNA replication.  相似文献   

Loads on Sprayed Waterproof Tunnel Linings in Jointed Hard Rock: A Study Based on Norwegian Cases     

Karl Gunnar Holter 《Rock Mechanics and Rock Engineering》2014,47(3):1003-1020

A composite tunnel lining system based on a sprayed waterproofing membrane combined with sprayed concrete is currently being considered for future Norwegian rail and road tunnels. Possible loading of the tunnel linings caused by water pressure is being investigated. This tunnel lining system consists of a waterproof membrane which, during application on the sprayed concrete lining, bonds mechanically to the sprayed concrete on either side. Hence, a continuous, sealing, and non-draining structure from the rock mass to the interior tunnel surface is formed in the walls and crown. Experiences from some successful recent projects with this lining system in Europe are reviewed. However, these experiences are not directly comparable to the Scandinavian hard rock tunnel lining approach, which utilizes a relatively thin sprayed and irregular concrete layer for permanent lining. When considering the sprayed membrane and sprayed concrete composite lining concept, introducing a partially sealing and undrained element in the lining, the experiences with the traditionally used lining systems in Norway need to be reconsidered and fully understood. A review of several hard rock tunnels with adverse conditions, in which the tunnel lining has been subject to load monitoring, shows that only very small loads in the tunnel linings occur. Recent investigations with in situ water pressure testing, including two sites with the composite sprayed membrane in a partially drained waterproof tunnel lining, are discussed. In a case with a cavern located in a hydraulically saturated rock mass subjected to approximately 8 bar hydrostatic pressure, a negative pressure gradient towards the tunnel lining has been measured. The investigation results from the Norwegian test sites indicate that no significant loading of the tunnel lining takes place in a hydraulically saturated rock when applying this composite waterproof tunnel lining in parts of the tunnel perimeter.  相似文献   

Non-ideal MHD Properties of Magnetic Flux Tubes in the Solar Photosphere     

Kleimann  Jens  Hornig  Gunnar 《Solar physics》2001,200(1-2):47-62

Magnetic flux tubes reaching from the solar convectivezone into the chromosphere have to pass through the relatively cool, and therefore non-ideal (i.e. resistive) photospheric region enclosed between the highly ideal sub-photospheric and chromospheric plasma. It is shown that stationary MHD equilibria of magnetic flux tubes which pass through this region require an inflow of photospheric material into the flux tube and a deviation from iso-rotation along the tube axis. This means that there is a difference in angular velocity of the plasma flow inside the tube below and above the non-ideal region. Both effects increase with decreasing cross section of the tube. Although for characteristic parameters of thick flux tubes the effect is negligible, a scaling law indicates its importance for small-scale structures. The relevance of this `inflow effect' for the expansion of flux tubes above the photosphere is discussed.  相似文献   

Human empowerment: Opportunities from ocean governance     

Gunnar Kullenberg 《Ocean & Coastal Management》2010,53(8):405-420

Stimulus to reach the millennium goals of poverty abatement and empowerment, including education and employment, for the large part of the population in the coastal zone can be found in the resources and services of oceans and coasts; the required financial means, given political will and right priorities, can be provided through implementation of the related international conventions, in particular UNCLOS with the EEZ, the Common Heritage of Mankind and other provisions, Agenda 21 [1] of UNCED and the WSSD 2002 Ocean Targets; the motivation is the necessity to address over-exploitation, depletion and destruction of resources, habitats and coastal ecosystem services, global changes, as well as economic transformations and social conditions of poverty, employment and unequity. Achieving adequate management and protection of natural assets as ecosystems and their services, habitats, biodiversity requires that the socio-economic and human security needs of the coastal populations are met. One way to reach the goal is to enable them, representing about 50% of the global population and increasing, to fight poverty and cope with uncertainties and changing conditions of employment, environment and sustainability through proper governance of the coastal and ocean assets. This includes provision of education and knowledge as regards these assets and their proper uses. They include energy, water, food, transportation and trade, communication, coastal developments, tourism, recreation and ecosystem services, as well as the need to properly manage them.The present economic system cannot fully harmonize with the required governance, partly since the ecosystem resources and services are not internalised in the market-oriented system. This calls for a revised education and training system, more comprehensive than the present, taking into account the social, cultural and environmental requirements, and stressing the sustainable development paradigm. In order to achieve ocean governance and comprehensive human security an understanding of the system is needed. This is substantiated through the Decade of Education for Sustainable Development as well as the Millennium Ecosystem Assessment.The aim here is to discuss some of the issues in context of implementation of related ocean conventions and commitments, which include achieving ocean governance, and to elucidate opportunities given by oceans and coasts, also in generating employment and providing for basic human needs.  相似文献   

The use of the Pareto distribution for fracture transmissivity assessment     

Gunnar Gustafson  Åsa Fransson 《Hydrogeology Journal》2006,14(1-2):15-20

For many applications data on the transmissivity distribution of individual fractures are necessary, i.e., discrete fracture network (DFN) modelling of groundwater flow and transport of solutes in fractured rock and design and performance of rock grouting. Using borehole data from the Äspö Hard Rock Laboratory, Sweden, it is shown that evaluated fracture transmissivities from three boreholes at Äspö can be well described by a Pareto or power-law distribution. Evaluated distribution parameters for the three boreholes are similar, which indicates that the Pareto distribution is a robust tool to assess three fracture transmissivity distributions. Using the evaluated distribution parameters random simulations of the original interval test data show that the approximate lognormal distributions of these are reproduced. This strengthens the credibility of the approach. It is shown how the distribution parameters can be assessed from incomplete data using the properties of the distribution. Finally, Pareto distribution transmissivities also imply Pareto distribution apertures of the fractures.

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Resumen Los datos sobre la distribución de la transmisividad en fracturas individuales, son necesarios para muchas aplicaciones, Ej. Modelación de redes de fracturamiento discreto (RFD) para flujo de agua subterránea y transporte de solutos en roca fracturada y para el diseño y ejecución de operaciones de cementación en roca. Mediante el uso del Laboratorio de Rocas Duras de Äspö en Suecia, se ha demostrado que las transmisividades por fractura evaluadas en tres perforaciones en Äspö pueden ser descritas bien por una distribución Pareto o Potencial. Los parámetros de distribución evaluados para las tres perforaciones son similares, lo cual indica que la distribución Pareto es una herramienta adecuada para evaluar tres distribuciones de transmisividad por fractura. Mediante el uso de simulaciones al azar, de los parámetros de distribución evaluados, a partir de los datos del intervalo de la prueba original, se muestra que las distribuciones lognormal así aproximadas de aquellos, pueden ser reproducidas. Esto refuerza la credibilidad del método. Se demuestra como los parámetros de distribución pueden ser evaluados a partir de datos incompletos, usando las propiedades de la distribución. Finalmente, las transmisividades con distribución Pareto, también implican aberturas de las fracturas con distribución Pareto.

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Résumé Pour beaucoup dapplications sont nécessaires des données sur la distribution des transmissivités des fractures individuelles; des exemples sont la modélisation de lécoulement et du transport dans les roches fracturés ainsi que lanalyse de performance de la cimentation des roches. Les données des forages analysées dans le Laboratoire des roches dures dÄsprö-Suède ont montré que la distribution des transmissivités des fractures estimée pour trois forages dÄsprö est en accord avec les lois de Pareto ou de puissance. paramètres pour trois forages ont des valeurs semblables ce quindique que la loi de Pareto peut bien évaluer la distribution des transmissivités des fractures. Les simulations aléatoires réalisés sur lintervalle original des données qui ont utilisé les paramètres estimés des distributions ont bien reproduit la distribution log-normale approximée. Ce résultat a consolidé la confiance dans lapproche faite. On a montré que les paramètres de la distribution peuvent être estimés à partir de données incomplètes si on utilise les propriétés de la distribution. Finalement, la distribution de Pareto pour les transmissivités implique la même loi pour la distribution de lépaisseur des fractures.

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On the regional distribution of mitigation costs in a global cap-and-trade regime     

Gunnar Luderer  Enrica DeCian  Jean-Charles Hourcade  Marian Leimbach  Henri Waisman  Ottmar Edenhofer 《Climatic change》2012,114(1):59-78

This paper analyzes the regional distribution of climate change mitigation costs in a global cap-and-trade regime. Four stylized burden-sharing rules are considered, ranging from GDP-based permit allocations to schemes that foresee a long-term convergence of per-capita emission permits. The comparison of results from three structurally different hybrid, integrated energy-economy models allows us to derive robust insights as well as identify sources of uncertainty with respect to the regional distribution of the costs of climate change mitigation. We find that regional costs of climate change mitigation may deviate substantially from the global mean. For all models, the mitigation cost average of the four scenarios is higher for China than for the other macro-regions considered. Furthermore, China suffers above-world-average mitigation costs for most burden-sharing rules in the long-term. A decomposition of mitigation costs into (a) primary (domestic) abatement costs and (b) permit trade effects, reveals that the large uncertainty about the future development of carbon prices results in substantial uncertainties about the financial transfers associated with carbon trade for a given allocation scheme. This variation also implies large uncertainty about the regional distribution of climate policy costs.  相似文献   

Helgoland Roads,North Sea: 45 Years of Change     

Karen Helen Wiltshire  Alexandra Kraberg  Inka Bartsch  Maarten Boersma  Heinz-Dieter Franke  Jan Freund  Christina Gebühr  Gunnar Gerdts  Karina Stockmann  Antje Wichels 《Estuaries and Coasts》2010,33(2):295-310

The Helgoland Roads time series is one of the richest temporal marine data sets available. Running since 1962, it documents changes for phytoplankton, salinity, Secchi disc depths and macronutrients. Uniquely, the data have been carefully quality controlled and linked to relevant meta-data, and the pelagic time series is further augmented by zooplankton, intertidal macroalgae, macro-zoobenthos and bacterioplankton data. Data analyses have shown changes in hydrography and biota around Helgoland. In the late 1970s, water inflows from the south-west to the German Bight increased with a corresponding increase in flushing rates. Salinity and annual mean temperature have also increased since 1962 and the latter by an average of 1.67°C. This has influenced seasonal phytoplankton growth causing significant shifts in diatom densities and the numbers of large diatoms (e. g. Coscinodiscus wailesii). Changes in zooplankton diversity have included the appearance of the ctenophore Mnemiopsis leidyi. The macroalgal community also showed an increase in green algal and a decrease in brown algal species after 1959. Over 30 benthic macrofaunal species have been newly recorded at Helgoland over the last 20 years, with a distinct shift towards southern species. These detailed data provide the basis for long-term analyses of changes on many trophic levels at Helgoland Roads.  相似文献   

Seismic imaging of the laterally varying D" region beneath the Cocos Plate   总被引：1，自引：0，他引：1  

Michael S. Thorne  Thorne Lay  Edward J. Garnero  Gunnar Jahnke †  Heiner Igel 《Geophysical Journal International》2007,170(2):635-648

We use an axisymmetric, spherical Earth finite difference algorithm to model SH -wave propagation through cross-sections of laterally varying lower mantle models beneath the Cocos Plate derived from recent data analyses. Synthetic seismograms with dominant periods as short as 4 s are computed for several models: (1) a D" reflector 264 km above the core–mantle boundary with laterally varying S -wave velocity increases of 0.9–2.6 per cent, based on localized structures from a 1-D double-array stacking method; (2) an undulating D" reflector with large topography and uniform velocity increase obtained using a 3-D migration method and (3) cross-sections through the 3-D mantle S -wave velocity tomography model TXBW. We apply double-array stacking to assess model predictions of data. Of the models explored, the S -wave tomography model TXBW displays the best overall agreement with data. The undulating reflector produces a double Scd arrival that may be useful in future studies for distinguishing between D" volumetric heterogeneity and D" discontinuity topography. Synthetics for the laterally varying models show waveform variability not observed in 1-D model predictions. It is challenging to predict 3-D structure based on localized 1-D models when lateral structural variations are on the order of a few wavelengths of the energy used, particularly for the grazing geometry of our data. Iterative approaches of computing synthetic seismograms and adjusting model characteristics by considering path integral effects are necessary to accurately model fine-scale D" structure.  相似文献