Empirical-statistical downscaling and error correction of regional climate models and its impact on the climate change signal   总被引：7，自引：3，他引：4  

Matthias Jakob Themeßl  Andreas Gobiet  Georg Heinrich 《Climatic change》2012,112(2):449-468

Realizing the error characteristics of regional climate models (RCMs) and the consequent limitations in their direct utilization in climate change impact research, this study analyzes a quantile-based empirical-statistical error correction method (quantile mapping, QM) for RCMs in the context of climate change. In particular the success of QM in mitigating systematic RCM errors, its ability to generate “new extremes” (values outside the calibration range), and its impact on the climate change signal (CCS) are investigated. In a cross-validation framework based on a RCM control simulation over Europe, QM reduces the bias of daily mean, minimum, and maximum temperature, precipitation amount, and derived indices of extremes by about one order of magnitude and strongly improves the shapes of the related frequency distributions. In addition, a simple extrapolation of the error correction function enables QM to reproduce “new extremes” without deterioration and mostly with improvement of the original RCM quality. QM only moderately modifies the CCS of the corrected parameters. The changes are related to trends in the scenarios and magnitude-dependent error characteristics. Additionally, QM has a large impact on CCSs of non-linearly derived indices of extremes, such as threshold indices.  相似文献   

Reconstruction of floodplain sedimentation rates: a combination of methods to optimize estimates     

Noortje Hobo  Bart Makaske  Hans Middelkoop  Jakob Wallinga 《地球表面变化过程与地形》2010,35(13):1499-1515

Reconstruction of overbank sedimentation rates over the past decades gives insight into floodplain dynamics, and thereby provides a basis for efficient and sustainable floodplain management. We compared the results of four independent reconstruction methods – optically stimulated luminescence (OSL) dating, caesium‐137 (¹³⁷Cs) dating, heavy metal analysis, and flood bed interpretation – applied at three embanked floodplain sites along lower Rhine River distributaries in the Netherlands. All methods indicate significant sedimentation rates on the floodplains, varying between 2–7 mm/a in the distal zones and 3–9 mm/a in the proximal zones. On a rapidly developing sand bar along a natural levee sedimentation rates of 9 to 25 mm/a were found. Except for some minor inconsistencies in ¹³⁷Cs dating results, all methods show decreasing sedimentation rates with increasing distance from the river channel. Intercomparison of the results of the different dating methods revealed the potential errors associated with each method, particularly where disagreement among the results were found. Uncertainties may arise due to (1) grain‐size dependent downward migration of ¹³⁷Cs, (2) smoothing of the vertical heavy metal and ¹³⁷Cs profiles, (3) delayed sediment‐associated input of ¹³⁷Cs in addition to direct atmospheric fall‐out, (4) overestimation of the burial age in OSL dating due to incomplete resetting of the OSL signal, or (5) non‐linear relationships between sediment deposition and flood magnitude in the count‐from‐the‐top correlation between sediment lamination and past observed flood records. Still, taking the uncertainties associated with each method into account, the results are generally in good agreement. Using the results we indicate the optimal spatial range of application of each method, depending on sediment texture and sedimentation rate. The optimal spatial and temporal ranges differ for each method, but show significant overlap. A combination of the methods will thus provide maximum information for accurate estimation of sedimentation rates on a decadal time scale. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

A debris-flow alarm system for the Alpine Illgraben catchment: design and performance   总被引：3，自引：2，他引：1  

Alexandre Badoux  Christoph Graf  Jakob Rhyner  Richard Kuntner  Brian W. McArdell 《Natural Hazards》2009,49(3):517-539

We describe the development, implementation, and first analyses of the performance of a debris-flow warning system for the Illgraben catchment and debris fan area. The Illgraben catchment (9.5 km²), located in the Canton of Valais, Switzerland, in the Rhone River valley, is characterized by frequent and voluminous sediment transport and debris-flow activity, and is one of the most active debris-flow catchments in the Alps. It is the site of an instrumented debris-flow observation station in operation since the year 2000. The residents in Susten (municipality Leuk), tourists, and other land users, are exposed to a significant hazard. The warning system consists of four modules: community organizational planning (hazard awareness and preparedness), event detection and alerting, geomorphic catchment observation, and applied research to facilitate the development of an early warning system based on weather forecasting. The system presently provides automated alert signals near the active channel prior to (5–15 min) the arrival of a debris flow or flash flood at the uppermost frequently used channel crossing. It is intended to provide data to support decision-making for warning and evacuation, especially when unusually large debris flows are expected to leave the channel near populated areas. First-year results of the detection and alert module in comparison with the data from the independent debris-flow observation station are generally favorable. Twenty automated alerts (alarms) were issued, which triggered flashing lights and sirens at all major footpaths crossing the channel bed, for three debris flows and 16 flood flows. Only one false alarm was issued. The major difficulty we encountered is related to the variability and complexity of the events (e.g., events consisting of multiple surges) and can be largely solved by increasing the duration of the alarm. All of the alarms for hazardous events were produced by storms with a rainfall duration and intensity larger than the threshold for debris-flow activity that was defined in an earlier study, supporting our intention to investigate the use of rainfall forecasts to increase the time available for warning and implementation of active countermeasures.  相似文献   

Use of particulate surrogates for assessing microbial mobility in subsurface ecosystems     

Michael Sinreich  Raymond Flynn  Jakob Zopfi 《Hydrogeology Journal》2009,17(1):49-59

Mass fluxes from the ground surface can play a vital role in influencing groundwater ecosystems. Rates of delivery may influence intact ecosystem composition, while fluxes of substances associated with anthropogenic activity may critically alter the functioning of associated microbial assemblages. Field-based tracing experiments offer a valuable means of understanding mass transport rates and mechanisms, particularly in complex heterogeneous epikarst systems overlying vulnerable fissured aquifers. A short-term tracer experiment monitoring solute and particle tracer concentrations after they passed through a 10-m-thick sequence of limestone, capped by a thin soil, revealed rapid travel times and variable attenuation rates for the substances employed. Results demonstrated that particle tracers have shorter average travel times and can reach the subsurface in higher concentrations and over shorter times than non-reactive solutes. High recovery rates for the bacterial tracer Ralstonia eutropha H16 contrasted strongly with those of similarly sized fluorescent polystyrene microspheres, highlighting the importance of physico-chemical surface characteristics of particle tracers. Complementary laboratory batch experiments examined the role played by organic and inorganic soil/rock surfaces on particle tracer attenuation. Findings suggest that biofilms may significantly promote transport of particulate material below ground, i.e., the delivery of allochthonous microorganisms to karst groundwater.  相似文献   

The Erbisberg drilling 2011: Implications for the structure and postimpact evolution of the inner ring of the Ries impact crater     

Gernot Arp  Andreas Reimer  Klaus Simon  Sebastian Sturm  Jakob Wilk  Corina Kruppa  Lutz Hecht  Bent T. Hansen  Jean Pohl  Wolf Uwe Reimold  Thomas Kenkmann  Dietmar Jung 《Meteoritics & planetary science》2019,54(10):2448-2482

The 26 km diameter Nördlinger Ries is a complex impact structure with a ring structure that resembles a peak ring. A first research drilling through this “inner crystalline ring” of the Ries was performed at the Erbisberg hill (SW Ries) to better understand the internal structure and lithology of this feature, and possibly reveal impact‐induced hydrothermal alteration. The drill core intersected the slope of a 22 m thick postimpact travertine mound, before entering 42 m of blocks and breccias of crystalline rocks excavated from the Variscan basement at >500 m depth. Weakly shocked gneiss blocks that show that shock pressure did not exceed 5 GPa occur above polymict lithic breccias of shock stage Ia (10–20 GPa), with planar fractures and planar deformation features (PDFs) in quartz. Only a narrow zone at 49.20–50.00 m core depth exhibits strong mosaicism in feldspar and {102} PDFs in quartz, which are indicative of shock stage Ib (20–35 GPa). Finally, 2 m of brecciated Keuper sediments at the base of the section point to an inverse layering of strata. While reverse grading of clast sizes in lithic breccias and gneiss blocks is consistent with lateral transport, the absence of diaplectic glass and melt products argues against dynamic overthrusting of material from a collapsing central peak, as seen in the much larger Chicxulub structure. Indeed, weakly shocked gneiss blocks are rather of local provenance (i.e., the transient crater wall), whereas moderately shocked polymict lithic breccias with geochemical composition and ⁸⁷Sr/⁸⁶Sr signature similar to Ries suevite were derived from a position closer to the impact center. Thus, the inner ring of the Ries is formed by moderately shocked polymict lithic breccias likely injected into the transient crater wall during the excavation stage and weakly shocked gneiss blocks of the collapsing transient crater wall that were emplaced during the modification stage. While the presence of an overturned flap is not evident from the Erbisberg drilling, a survey of all drillings at or near the inner ring point to inverted strata throughout its outer limb. Whether the central ring of the Ries represents remains of a collapsed central peak remains to be shown. Postimpact hydrothermal alteration along the Erbisberg section comprises chloritization, sulfide veinlets, and strong carbonatization. In addition, a narrow zone in the lower parts of the polymict lithic breccia sequence shows a positive Eu anomaly in its carbonate phase. The surface expression of this hydrothermal activity, i.e., the travertine mound, comprises subaerial as well as subaquatic growth phases. Intercalated lake sediments equivalent to the early parts of the evolution of the central crater basin succession confirm a persistent impact‐generated hydrothermal activity, although for less time than previously suggested.  相似文献   

Hebung — Spaltung — Vulkanismus V. Ein Scheitelgraben in einem Faltensattel des Siegerlandes     

Jakob Andres 《International Journal of Earth Sciences》1940,31(3-4):241-243

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Statistical and hydrodynamic models for the operational forecasting of floods in the Venice Lagoon     

Jos Vieira  Jakob Fns  Giovanni Cecconi 《Coastal Engineering》1993,21(4)

The risk of flooding in Venice has increased strongly since the beginning of the century. To reduce the damage to the city and the negative impact on the activities in the lagoon, an accurate flood warning system is necessary. This system will also be fundamental during the construction and for the efficient operation of storm surge barriers covering the three existing inlets of the lagoon. In this context new operational statistical and hydrodynamic models have been developed. Forecast winds and pressure fields which constitute basic information for the warning system have been obtained through an ad hoc Limited Area Meteorological model. It has been demonstrated that, provided that this information is available on an operational basis, the implementation of a flood warning system for Venice using the models developed is feasible. The statistical model, which is based on a multiple regression technique, extends the forecasting range of the model presently in operation at the Centro Previsioni e Segnalazioni Maree del Comune di Venezia, from 3 hrs up to 24 hrs, and presents good accuracy (estimated mean absolute errors smaller than 10 cm) for short-term forecasts up to 9 hrs. The hydrodynamic model includes all the physical processes important for the simulation of water levels and currents in coastal and marine environments. The model set-up adopted covers the entire Adriatic Sea, with a grid spacing of 6 km. Special attention has been given to the positioning of the open boundary and to the correct reproduction of the main free oscillation of the Adriatic, which is responsible for the possible recurrence of flooding after the main storm has passed. The inclusion of this model in a flood warning system is mainly intended for long-term forecasts (> 24 hrs), and can typically be used to forecast up to 3–4 days ahead, with an estimated mean absolute error smaller than 20 cm.  相似文献   

Seasonal feeding ecology of cod (Gadus morhua L.) on the Norwegian Skagerrak coast     

Hop  Haakon; Gjosaeter  Jakob; Danielssen  Didrik S. 《ICES Journal of Marine Science》1992,49(4):453-461

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Biogeochemistry of sulfur and iron in Thioploca-colonized surface sediments in the upwelling area off central chile     

Jakob Zopfi  Bo Barker Jørgensen 《Geochimica et cosmochimica acta》2008,72(3):827-843

The biogeochemistry of sedimentary sulfur was investigated on the continental shelf off central Chile at water depths between 24 and 88 m under partial influence of an oxygen minimum zone. Dissolved and solid iron and sulfur species, including the sulfur intermediates sulfite, thiosulfate, and elemental sulfur, were analyzed at high resolution in the top 20 cm. All stations were characterized by high rates of sulfate reduction, but only the sediments within the Bay of Concepción contained dissolved sulfide. Due to advection and/or in-situ reoxidation of sulfide, dissolved sulfate was close to bottom water values. Whereas the concentrations of sulfite and thiosulfate were mostly in the submicromolar range, elemental sulfur was by far the dominant sulfur intermediate. Although the large nitrate- and sulfur-storing bacteria Thioploca were abundant, the major part of S⁰ was located extracellularly. The distribution of sulfur species and dissolved iron suggests the reaction of sulfide with FeOOH as an important pathway for sulfide oxidation and sulfur intermediate formation. This is in agreement with the sulfur isotope composition of co-existing elemental sulfur and iron monosulfides. In the Bay of Concepción, sulfur isotope data suggest that pyrite formation proceeds via the reaction of FeS with polysulfides or H₂S. At the shelf stations, on the other hand, pyrite was significantly depleted in ³⁴S relative to its potential precursors FeS and S⁰. Isotope mass balance considerations suggest further that pyritization at depth includes light sulfide, potentially originating from bacterial sulfur disproportionation. The δ³⁴S-values of pyrite down to −38‰ vs. V-CDT are among the lightest found in organic-rich marine sediments. Seasonal variations in the sulfur isotope composition of dissolved sulfate indicated a dynamic non-steady-state sulfur cycle in the surface sediments. The ¹⁸O content of porewater sulfate increased with depth at all sites compared to the bottom water composition due to intracellular isotope exchange reactions during microbial sulfur transformations.  相似文献   

Astronomical-topographic levelling using high-precision astrogeodetic vertical deflections and digital terrain model data   总被引：2，自引：1，他引：1  

Christian Hirt  Jakob Flury 《Journal of Geodesy》2008,82(4-5):231-248

At the beginning of the twenty-first century, a technological change took place in geodetic astronomy by the development of Digital Zenith Camera Systems (DZCS). Such instruments provide vertical deflection data at an angular accuracy level of 0.̋1 and better. Recently, DZCS have been employed for the collection of dense sets of astrogeodetic vertical deflection data in several test areas in Germany with high-resolution digital terrain model (DTM) data (10–50 m resolution) available. These considerable advancements motivate a new analysis of the method of astronomical-topographic levelling, which uses DTM data for the interpolation between the astrogeodetic stations. We present and analyse a least-squares collocation technique that uses DTM data for the accurate interpolation of vertical deflection data. The combination of both data sets allows a precise determination of the gravity field along profiles, even in regions with a rugged topography. The accuracy of the method is studied with particular attention on the density of astrogeodetic stations. The error propagation rule of astronomical levelling is empirically derived. It accounts for the signal omission that increases with the station spacing. In a test area located in the German Alps, the method was successfully applied to the determination of a quasigeoid profile of 23 km length. For a station spacing from a few 100 m to about 2 km, the accuracy of the quasigeoid was found to be about 1–2 mm, which corresponds to a relative accuracy of about 0.05−0.1 ppm. Application examples are given, such as the local and regional validation of gravity field models computed from gravimetric data and the economic gravity field determination in geodetically less covered regions.  相似文献