IMAGE: a multivariate multi-site stochastic weather generator for European weather and climate     

Nathan?J.?SparksEmail authorView author&#;s OrcID profile  Stephen?R.?Hardwick  Matthias?Schmid  Ralf?Toumi 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(3):771-784

Capturing the spatial and temporal correlation of multiple variables in a weather generator is challenging. A new massively multi-site, multivariate daily stochastic weather generator called IMAGE is presented here. It models temperature and precipitation variables as latent Gaussian variables with temporal behaviour governed by an auto-regressive model whose residuals and parameters are correlated through resampling of principle component time series of empirical orthogonal function modes. A case study using European climate data demonstrates the model’s ability to reproduce extreme events of temperature and precipitation. The ability to capture the spatial and temporal extent of extremes using a modified Climate Extremes Index is demonstrated. Importantly, the model generates events covering not observed temporal and spatial scales giving new insights for risk management purposes.  相似文献   

Shear-wave velocity estimation using a combination of ambient noise from small aperture array and small-scale active seismic measurements: a case study in the area of the natural gas fields of Northern Germany     

Moritz Fehr  Simon Kremers  Ralf Fritschen 《Journal of Seismology》2018,22(6):1359-1376

In recent years, numerous induced seismic events have occurred in the proximity of the natural gas field in Northern Germany. To monitor the seismicity and to asses the seismic hazard potential, a local monitoring network was installed in the area. Focusing on the seismicity hazard assessment, a major challenge is the characterisation of potential site effects due to local soil characteristics. This is quantitatively performed by estimating the shear-wave velocity (V _s) variation with subsurface layer thickness. Such local effects can only be covered with a coarse spatial resolution due to the limited number of monitoring stations. Profiles were determined at three test sites (Langwedel, Walle and Bomlitz) by using a combined approach of small aperture 2D array ambient noise and small-scale active 1D measurements. The high-resolution frequency-wavenumber (HRFK), spatial autocorrelation (SPAC) and multichannel analysis of surface waves (MASW) methods were applied to the recorded ambient noise and active seismic data using various array sizes supplemented by the active measurements. This jointly allowed obtaining phase velocity dispersion curves covering a wide frequency range from 2 up to 32 Hz. The inversion of the obtained dispersion curves results in average S-wave velocity profiles down to depths of 70 m, identifying thin near-surface layers of a few meters as well as thicker layers of tens of meters in greater depth. A comparison with available borehole data shows a good correlation with the layering. Additionally, to asses the impact of a seismic event at the test sites, PGV estimations for various seismic events were performed. The final results of the test surveys demonstrate that the combined approach represents a suitable tool for near-surface characterisation, which can be used to improve the seismic hazard assessment in the area of the natural gas fields in Northern Germany.  相似文献   

Communicating landscape hydrology — the water cycle in a box          下载免费PDF全文

Christian Lehr  Philipp Rauneker  Marcus Fahle  Tobias L. Hohenbrink  Steven Böttcher  Marco Natkhin  Björn Thomas  Ralf Dannowski  Bernd Schwien  Gunnar Lischeid 《水文研究》2017,31(3):750-752

Physical models are a well‐established tool in education to strengthen hydrological understanding. They facilitate the straightforward visualization of hydrological processes and allow the communication of hydrological concepts, research and questions of general interest to the public. In order to visualize the water cycle in a landscape of postglacial sediments, in particular the subsurface part, a physical model was constructed. In two videos, (1) a detailed construction manual and (2) visualization examples of hydrological concepts and processes are presented. With our contribution, we like to encourage professionals in the field of hydrology to share methods and tools of knowledge transfer and communication of hydrological concepts. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Role of climate changes for wind gap formation in a young,actively growing mountain range          下载免费PDF全文

Andrea Hampel  Ralf Hetzel 《地学学报》2016,28(6):441-448

Wind gaps in actively growing mountain ranges are unique geomorphological features testifying to the competition between tectonics and fluvial incision. Although it is clear that these landforms reflect the defeat of rivers during sustained rock uplift, the role of climate changes in their formation has never been explored. Here, we use a coupled tectonics–landscape evolution model to show that temporal changes in precipitation rate exert an important control on wind gap formation. In models with a constant precipitation rate, rivers flowing across a growing range are either defeated at an early stage or they abandon their valleys very late, if at all. If precipitation varies, wind gaps form mostly c. 100–200 ka after a transition to drier conditions because of sediment aggradation upstream of the range. Our results suggest that the Pliocene–Quaternary aridification of Central Asia contributed to wind gap formation in active mountain ranges in the foreland of northeastern Tibet.  相似文献   

The Epochs of Early-Type Galaxy Formation     

Daniel Thomas  Claudia Maraston  Ralf Bender 《Astrophysics and Space Science》2002,281(1-2):371-374

By means of population synthesis models with variable α/Fe ratios we derive average ages, metallicities, and [α/Fe] element enhancements for a sample of 126 field and cluster early-type galaxies. We find a clear positive relation between [α/Fe] and velocity dispersion. Zero-point, slope, and scatter of this correlation are the same for cluster and field galaxies. In particular, the [α/Fe] ratios and mean ages of cluster ellipticals are positively correlated. This strongly reinforces the view that the [α/Fe] element enhancement in ellipticals is produced by star formation timescales rather than by variations of the initial mass function. These results indicate that the more massive the galaxy, the shorter is its star formation timescale, and the higher is the redshift of the bulk of star formation. This finding is not compatible with the predictions from models of hierarchical galaxy formation. The lenticular and field galaxies of the investigated sample do not follow the correlation between age and [α/Fe], but contain a non-negligible fraction of galaxies with young average ages and high [α/Fe] ratios. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

The Decay of Supersonic and Super-Alfvénic Turbulence in Star-Forming Clouds     

Mordecai-Mark Mac Low  Michael D. Smith  Ralf S. Klessen  Andreas Burkert 《Astrophysics and Space Science》1998,261(1-4):195-196

Supersonic and super-Alfvénic turbulent motions generate an intricate pattern of shock waves through which the turbulence decays. We here illustrate the spatial structure during shock formation and decay. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Impact of Lateglacial cold events on the northern Aegean region reconstructed from marine and terrestrial proxy data     

Ulrich Kotthoff  Andreas Koutsodendris  Jörg Pross  Gerhard Schmiedl  André Bornemann  Christian Kaul  Gianluca Marino  Odile Peyron  Ralf Schiebel 《第四纪科学杂志》2011,26(1):86-96

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Catchment‐wide denudation rates at the margin of NE Tibet from in situ‐produced cosmogenic 10Be     

Luigi Palumbo  Ralf Hetzel  Mingxin Tao  Xiaobin Li 《地学学报》2011,23(1):42-48

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Computational modeling of flow‐induced anisotropy of polar ice for the EDML deep drilling site,Antarctica: The effect of rotation recrystallization and grain boundary migration     

Swantje Bargmann  Hakime Seddik  Ralf Greve 《国际地质力学数值与分析法杂志》2012,36(7):892-917

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Determination of the conduit structure in a karst aquifer based on tracer data—Lurbach system,Austria     

Christine Kübeck  Piotr Jan Maloszewski  Ralf Benischke 《水文研究》2013,27(2):225-235

A structure model was used to analyse solute‐transport parameter estimates based on tracer breakthrough curves. In the model system, groundwater flow is envisioned to be organised in a complex conduit network providing a variety of short circuits with relative small carrying capacities along different erosion levels. The discharge through the fully filled conduits is limited owing to void geometries and turbulent flow; thus, a hierarchic overflow system evolves where conduits are (re‐)activated or dried up depending on the flow condition. Exemplified on the Lurbach–Tanneben karst aquifer, the applicability of the model approach was tested. Information derived from multi‐tracer experiments performed at different volumetric flow rates enabled to develop a structural model of the karst network, under constraint of the geomorphological and hydrological evolution of the site. Depending on the flow rate, groundwater is divided into up to eight flow paths. The spatial hierarchy of flow paths controls the sequence of flow path activation. Conduits of the topmost level are strongly influenced by reversible alteration processes. Sedimentation or blocking causes an overflow of water to the next higher conduit. Flow path specific dissolutional denudation rates were estimated using the temporal development of the partial discharge. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献