Stochastic Seismic Emission from Acoustic Glories and the Quiet Sun     

Donea  A.-C.  Lindsey  C.  Braun  D.C. 《Solar physics》2000,192(1-2):321-333

Helioseismic images of multipolar active regions show enhanced seismic emission in 5-mHz oscillations in a halo surrounding the active region called the `acoustic glory'. The acoustic glories contain elements that sustain an average seismic emission 50% greater than similar elements in the quiet Sun. The most intense seismic emitters tend to form strings in non-magnetic regions, sometimes marking the borders of weak magnetic regions and the separation between weak magnetic regions of opposite polarity. This study compares the temporal character of seismic emission from acoustic glories with that from the quiet Sun. The power distribution of quiet-Sun seismic emission far from solar activity is exponential, as for random Gaussian noise, and therefore not perceivably episodic. The distribution of seismic power emanating from the most intense elements that comprise the acoustic glories is exponential out to approximately 4 times the average power emitted by the quiet Sun. Above this threshold the latter distribution shows significant saturation, suggesting the operation of a hydromechanical non-linearity that sets limits on the acoustic power generated by the convection zone. This could give us considerable insight into the physical mechanism of seismic emission from the near subphotosphere.  相似文献   

Soil production and hillslope transport in mid‐latitudes during the last glacial–interglacial cycle: a combined data and modelling approach in northern Ardennes          下载免费PDF全文

Benoît Bovy  Jean Braun  Alain Demoulin 《地球表面变化过程与地形》2016,41(12):1758-1775

The relative efficiency of various hillslope processes through Quaternary glacial–interglacial cycles in the mid‐latitudes is not yet well constrained. Based on a unique set of topographic and soil thickness data in the Ardennes (Belgium), we combine the new CLICHE model of climate‐dependent hillslope evolution with an inversion algorithm in order to get deeper insight into the ways and timing of hillslope dynamics under one such climatic cycle. We simulate the evolution of a synthetic hill reproducing the slope, curvature, and contributing area distributions of the hillslopes of a ~ 2500 km² real area under a simple two‐stage 120‐kyr‐long climatic scenario with linear transitions between cold and warm stages. The inversion method samples a misfit function in the model parameter space, based on estimates of the fit of topographic derivative distributions in classes of soil thickness and of the relative frequencies of the predicted soil thickness classes. Though the inversion results show remarkable convergence patterns for most parameters, no unique solution emerges. We obtain five clusters of good fits, whose centroids are taken as acceptable model solutions. Based on the predicted time series of average denudation rate and soil thickness, plus snapshots of the soil distribution at characteristic times, we discuss these solutions and, comparing them with independent data not involved in the misfit function, we identify the most realistic scenario. Beyond providing first‐order estimates of several parameters that compare well with published data, our results show that denudation rates increase dramatically for a short time at both warm–cold and cold–warm transitions, when the mean annual temperature passes through the [0, ?5 °C] range. We also point to the overwhelming importance of solifluction in shaping hillslopes and transporting soil, and the role of depth‐dependent creep (including frost creep) throughout the climatic cycle, whereas the contributions of simple creep and overland flow are minor. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Comparison of Snow Data Assimilation System with GPS reflectometry snow depth in the Western United States          下载免费PDF全文

J. J. Braun  J. L. McCreight  F. G. Nievinski 《水文研究》2015,29(10):2425-2437

In this study, we compare gridded snow depth estimates from the Snow Data Assimilation System (SNODAS) with snow depth observations derived from GPS interferometric reflectometry (GPS‐IR) from roughly 100 Plate Boundary Observatory sites in the Western United States spanning four water‐years (2010–2013). Data from these sites are not assimilated by SNODAS; thus, GPS‐IR measurements provide an independent data set to evaluate SNODAS. Our results indicate that at 80% of the sites, SNODAS and GPS‐IR snow depth agree to better than 15‐cm root mean square error, with correlation coefficients greater than 0.6. Significant differences are found between GPS‐IR and SNODAS for sites that are distant from other point measurements, are located in complex terrain or are in areas with strong vegetation heterogeneities. GPS‐IR estimates of snow depth are shown to provide useful error characterization of SNODAS products across much of the Western United States and may have potential as an additional data assimilation source that could help improve SNODAS estimates. © 2014 The Authors. Hydrological Processes published by John Wiley & Sons Ltd.  相似文献   

The initiation of pull‐apart basins and transform continental margins: results from numerical experiments of kinematic partitioning in divergent settings          下载免费PDF全文

Christophe Basile  Jean Braun 《地学学报》2016,28(2):120-127

We present a set of numerical models to investigate how transform faults initiate in pull‐apart basins or transform continental margins. The model represents an elastic plate with three aligned weak spots. Applying strain on the edge of the model firstly propagates extensional cracks from the pre‐existing damaged spots. The subsequent evolution depends on the angle (obliquity) between the applied strain and the alignment of the damaged spots. For obliquity <50°, transform faults form to connect en‐échelon divergent cracks; for obliquity >60°, transtensional transfer zones connect the divergent cracks and no transform fault forms. These experiments suggest that pull‐apart basins do not form as previously assumed by connection of overlapping transform faults, but that transform faults form as connections of extensional areas.  相似文献   

Linking uplift,erosion, and sedimentation using landscape evolution models: Madagascar since the Late Cretaceous     

Ruohong Jiao  Jean Braun  Antoine Delaunay  Cécile Robin  François Guillocheau 《地球表面变化过程与地形》2023,48(1):215-229

We present a study to estimate the large-scale landscape history of a continental margin, by establishing a source-to-sink volume balance between the eroding onshore areas and the offshore basins. Assuming erosion as the primary process for sediment production, we strive to constrain a numerical model of landscape evolution that balances the volumes of eroded materials from the continent and that deposited in the corresponding basins, with a ratio imposed for loss of erosion products. We use this approach to investigate the landscape history of Madagascar since the Late Cretaceous. The uplift history prescribed in the model is inferred from elevations of planation surfaces formed at various ages. By fitting the volumes of terrigenous sediments in the Morondava Basin along the west coast and the current elevation of the island, the landscape evolution model is optimized by constraining the erosion law parameters and ratios of sediment loss. The results include a best-fit landscape evolution model, which features two major periods of uplift and erosion during the Late Cretaceous and the middle to late Cenozoic. The model supports suggestions from previous studies that most of the high topography of the island was constructed since the middle to late Miocene, and on the central plateau the erosion has not reached an equilibrium with the high uplift rates in the late Cenozoic. Our models also indicate that over the geological time scale a significant portion of materials eroded from Madagascar was not archived in the offshore basin, possibly consumed by chemical weathering, the intensity of which might have varied with climate.  相似文献   

Zielvorgaben für Pflanzenschutzmittelwirkstoffe und andere Schadstoffe in Oberflächengewässern     

Jutta Jahnel  Christian Zwiener  Thomas J. Gremm  Gudrun Abbt‐Braun  Fritz H. Frimmel  Carola Kussatz  Dieter Schudoma  Werner Rocker 《洁净——土壤、空气、水》2001,29(4):246-253

Quality Targets for Pesticides and Other Pollutants in Surface Waters Surface waters are not only adversely affected by industrial and municipal wastewaters but also by diffuse sources. For the control of the ecological water quality, so‐called quality targets are set. The quality targets are threshold concentrations for hazardous substances related to the protected goods like water ecosystems, drinking water supply, sediments, or fishing. In this paper, quality targets for the protection of aquatic life in surface waters were derived on the basis of a concept developed by the International Commission for the Protection of the Rhine (Internationale Kommission zum Schutze des Rheins – IKSR). The quality targets for the selected hazardous substances, which mainly belong to the chemical class of pesticides, were calculated using ecotoxicological results for species of bacteria, algae, fish, and small crustaceans, as the four trophic standards of the water ecosystem. In cooperation with the Federal Environmental Agency (Umweltbundesamt – UBA) the effect data were taken from ecotoxicological data bases. According to the concept of the IKSR, the lowest test result for the most sensitive species was multiplied by an assessment factor. This proceeding concerns the difficulty in describing the complex interactions in water ecosystems with toxicity data of single laboratory experiments for a few organisms. For seven pesticides quality targets below 0.1 μg/L were proposed. These results show that the ecotoxicologically based quality targets might be even lower than the limit values for pesticides in drinking water of 0.1 μg/L. But for most of the substances the determined values are significantly higher. The great concentration range of quality targets demonstrates distinctly that one standard concentration for all pesticides could not be given with regard to the different effects on aquatic organisms.  相似文献   

Bloom of the Yessotoxin producing dinoflagellate Protoceratium reticulatum (Dinophyceae) in Northern Chile     

Gonzalo Álvarez  Eduardo Uribe  Rosario Díaz  Mauricio Braun  Carmen Mariño  Juan Blanco 《Journal of Sea Research》2011,65(4):427-434

Potential spawning habitat is defined as the area where environmental conditions are suitable for spawning to occur. Spawning adult data from the first quarter (January–March) of the International Bottom Trawl Survey have been used to study the inter-annual variability of the potential spawning habitat of North Sea plaice from 1980 to 2007. Generalised additive models (GAM) were used to create a model that related five environmental variables (depth, bottom temperature and salinity, seabed stress and sediment type) to presence–absence and abundance of spawning adults. Then, the habitat model was applied each year from 1970 to 2007 to predict inter-annual variability of the potential spawning habitat. Predicted responses obtained by GAM for each year were mapped using kriging. A hierarchical classification associated with a correspondence analysis was performed to cluster spawning suitable areas and to determine how they evolved across years. The potential spawning habitat was consistent with historical spawning ground locations described in the literature from eggs surveys. It was also found that the potential spawning habitat varied across years. Suitable areas were located in the southern part of the North Sea and along the eastern coast of England and Scotland in the eighties; they expanded further north from the nineties. Annual survey distributions did not show such northward expansion and remained located in the southern North Sea. This suggests that this species' actual spatial distribution remains stable against changing environmental conditions, and that the potential spawning habitat is not fully occupied. Changes in environmental conditions appear to remain within plaice environmental ranges, meaning that other factors may control the spatial distribution of plaice spawning habitat.  相似文献   

Delineating spring recharge areas in a fractured sandstone aquifer (Luxembourg) based on pesticide mass balance     

J. Farlin  L. Drouet  T. Gallé  D. Pittois  M. Bayerle  C. Braun  P. Maloszewski  J. Vanderborght  M. Elsner  A. Kies 《Hydrogeology Journal》2013,21(4):799-812

A simple method to delineate the recharge areas of a series of springs draining a fractured aquifer is presented. Instead of solving the flow and transport equations, the delineation is reformulated as a mass balance problem assigning arable land in proportion to the pesticide mass discharged annually in a spring at minimum total transport cost. The approach was applied to the Luxembourg Sandstone, a fractured-rock aquifer supplying half of the drinking water for Luxembourg, using the herbicide atrazine. Predictions of the recharge areas were most robust in situations of strong competition by neighbouring springs while the catchment boundaries for isolated springs were extremely sensitive to the parameter controlling flow direction. Validation using a different pesticide showed the best agreement with the simplest model used, whereas using historical crop-rotation data and spatially distributed soil-leaching data did not improve predictions. The whole approach presents the advantage of integrating objectively information on land use and pesticide concentration in spring water into the delineation of groundwater recharge zones in a fractured-rock aquifer.  相似文献   

Erratum to: Nanoscale zero-valent iron flakes for groundwater treatment     

R. Köber  H. Hollert  G. Hornbruch  M. Jekel  A. Kamptner  N. Klaas  H. Maes  K.-M. Mangold  E. Martac  A. Matheis  H. Paar  A. Schäffer  H. Schell  A. Schiwy  K. R. Schmidt  T. J. Strutz  S. Thümmler  A. Tiehm  J. Braun 《Environmental Earth Sciences》2016,75(6):532

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The use of GPS for marine positioning in Germany—requirements,experience, and concepts     

Wolfgang Lechner  Gunther Braun  Harry Wirth 《Marine Geodesy》2013,36(3-4):233-241

Abstract

While beginning to establish a German Civil GPS Information and Observation Service in 1990, the actual and (near) future GPS market in Germany was analyzed. In addition, the feasibility of using GPS for water authority tasks has been studied during past years. Typical capabilities in this area are real‐time positioning for hydrographic surveying (kinematic application) and precise transfer of levels to tide gauges and verification at offshore positions.

The article describes the user interests, the requirements, some of the test campaigns, and the derived concepts for future applications.  相似文献