3D dynamics of debris flows quantified at sub-second intervals from laser profiles     

Mylène Jacquemart  Lorenz Meier  Christoph Graf  Felix Morsdorf 《Natural Hazards》2017,89(2):785-800

We use pairs of parallel mounted laser profile scanners to measure main debris-flow variables in two debris-flow channels in central and southern Switzerland. The scanners measure the instantaneous cross-sectional geometry of debris flows at rates of 25–100 Hz, and we apply large-scale particle image velocimetery to estimate velocity. The scanners also provide direct measurements of flow depth. From these data, we were able to estimate debris-flow depth, velocity and discharge for 16 out of 17 events. These results are consistent with discharge estimated from a system of geophones and a radar gauge for two available datasets. We also investigated debris-flow geometry to quantify rheology-controlled cross-flow convexity and found that four events manifest strong surface convexity at their surge fronts where we expect the largest boulders and low pore-fluid pressures. The scanners provide a completely new view of debris-flow dynamics and channel morphology and present novel opportunities to measure discharge and investigate debris-flow geometries.  相似文献   

Effect of climate change on the thermal stratification of the baltic sea: a sensitivity experiment     

R. Hordoir  H. E. M. Meier 《Climate Dynamics》2012,38(9-10):1703-1713

The evolution in time of the thermal vertical stratification of the Baltic Sea in future climate is studied using a 3D ocean model. Comparing periods at the end of the twentieth and twenty first centuries we found a strong increase in stratification at the bottom of the mixed layer in the northern Baltic Sea. In order to understand the causes of this increase, a sensitivity analysis is performed. We found that the increased vertical stratification is explained by a major change in re-stratification during spring solely caused by the increase of the mean temperature. As in present climate winter temperatures in the Baltic are often below the temperature of maximum density, warming causes thermal convection. Re-stratification during the beginning of spring is then triggered by the spreading of freshwater. This process is believed to be important for the onset of the spring bloom. In future climate, temperatures are expected to be usually higher than the temperature of maximum density and thermally induced stratification will start without prior thermal convection. Thus, freshwater controlled re-stratification during spring is not an important process anymore. We employed a simple box model and used sensitivity experiments with the 3D ocean model to delineate the processes involved and to quantify the impact of changing freshwater supply on the thermal stratification in the Baltic Sea. It is suggested that these stratification changes may have an important impact on vertical nutrient fluxes and the intensity of the spring bloom in future climate of the Baltic Sea.  相似文献   

Regional review: the hydrology of the Okavango Delta, Botswana—processes, data and modelling     

Christian Milzow  Lesego Kgotlhang  Peter Bauer-Gottwein  Philipp Meier  Wolfgang Kinzelbach 《Hydrogeology Journal》2009,17(6):1297-1328

The wetlands of the Okavango Delta accommodate a multitude of ecosystems with a large diversity in fauna and flora. They not only provide the traditional livelihood of the local communities but are also the basis of a tourism industry that generates substantial revenue for the whole of Botswana. For the global community, the wetlands retain a tremendous pool of biodiversity. As the upstream states Angola and Namibia are developing, however, changes in the use of the water of the Okavango River and in the ecological status of the wetlands are to be expected. To predict these impacts, the hydrology of the Delta has to be understood. This article reviews scientific work done for that purpose, focussing on the hydrological modelling of surface water and groundwater. Research providing input data to hydrological models is also presented. It relies heavily on all types of remote sensing. The history of hydrologic models of the Delta is retraced from the early box models to state-of-the-art distributed hydrological models. The knowledge gained from hydrological models and its relevance for the management of the Delta are discussed.  相似文献   

Determination of atmospheric composition and temperature from the u.v. airglow     

R.R. Meier  D.E. Anderson 《Planetary and Space Science》1983,31(9):967-976

Recent spectroscopic observations of atmospheric emissions in the u.v. region of the spectrum have been analyzed using laboratory-measured excitation cross-sections, models and observations of energetic electron fluxes and models of atmospheric composition. In both the airglow and the aurora, self-consistent pictures of the excitation processes and atmospheric composition have been obtained. These analyses have shown that photoelectron fluxes measured from the Atmospheric Explorer satellite are in good agreement with the photoelectron-excited dayglow and that a large number of recent laboratory-measured excitation processes are able to reproduce the u.v. spectra in both the dayglow and aurora. In this paper we show that accurate quantitative determinations of thermospheric parameters can now be made from u.v. spectral observations. In particular, we show that the composition and temperature can be obtained from altitude profiles of the emissions alone, without reliance on the absolute photoelectron flux.  相似文献   

The Health of Glaciers: Recent Changes in Glacier Regime   总被引：2，自引：1，他引：2  

Mark F. Meier  Mark B. Dyurgerov  Gregory J. McCabe 《Climatic change》2003,59(1-2):123-135

Glacier wastage has been pervasive during the last century; small glaciers and those in marginal environments are disappearing, large mid-latitude glaciers are shrinking slightly, and arctic glaciers are warming. Net mass balances during the last 40 years are predominately negative and both winter and summer balances (accumulation and ablation) and mass turnover are increasing, especially after 1988. Two principal components of winter balance time-series explain about 50% of the variability in the data. Glacier winter balances in north and central Europe correlate with the Arctic Oscillation, and glaciers in western North America correlate with the Southern Oscillation and Northern Hemisphere air temperature. The degree of synchronization for distant glaciers relates to changes in time of atmospheric circulation patterns as well as differing dynamic responses.  相似文献   

Automated multimode inversion of surface and S waveforms     

Sergei Lebedev  Guust Nolet  Thomas Meier  Rob D. van der Hilst 《Geophysical Journal International》2005,162(3):951-964

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Automated Ion-pair extraction and Ion-pair chromatography — a versatile method in water analysis for the determination of highly polar micropollutants     

F. Th. Lange  U. Meier  M. Wenz  H.-J. Brauch 《洁净——土壤、空气、水》1995,23(1):6-12

An automated HPLC method is presented which combines on-line ion-pair extraction on small exchangeable RP-C18 precolumns (RP-IPE) with ion-pair chromatography (RP-IPC). Weakly acidic herbicides — carboxylic acids, phenols, and the N-H acidic bentazone — and strong acids, e.g. aromatic sulfonic acids, can be determined simultaneously. Performance data are given. The tetrabutylammonium ion pairs of all investigated compounds are readily transferred from the RP-C18 precolumn to the analytical column by a phosphate buffer/methanol gradient. This is also true for the chlorinated phenoxy acids which, in earlier off-line extraction experiments, could not be desorbed from the RP-C18 material by the lower polar acetone. The RP-IPC is carried out at neutral pH where weakly acidic compounds appear in their stronger UV absorbing dissociated form. Compared to conventional reversed phase chromatography using an acidified eluent, the sensitivity of UV detection is markedly enhanced, especially for the phenol herbicides and bentazone. In addition, phenols can be detected more selectively because they show a second intense absorption band in the wavelength range between 280 nm and 290 nm, where there are only little interferences with the matrix. Due to miniaturization and automation, the online combination IPE/IPC allows a large sample throughput at a lower consumption of solid phase material and organic solvents. Time consuming manual steps are totally missing. The IPE/IPC technique is well suited as a screening method for fate studies of polar micropollutants, e. g. for monitoring the efficiency of different water treatment technologies. An example for balancing an activated carbon filter is presented.  相似文献   

Ein einfaches Modell zur Simulation der Schwermetallmigration im Boden     

J. Pelzer  B.-M. Bhmer  U. Meier 《洁净——土壤、空气、水》1989,17(6):659-666

The heavy-metal ions are bonded in the soil in different ways. With increasing concentration in the soil the soluble share of heavy-metal ions which is transported by the percolation water into lower soil layers and finally into the ground-water grows. The decrease of the distribution quotients and sorption capacities in the lead > cadmium series can be explained by the form of bonding at the soils which is specific to heavy metals. The elements are fixed as monohydroxo complexes. The heavy-metal retention capacity decreases with increasing time of introduction. For the estimation of the migration of heavy metals in agriculturally used soils it is recommended to combine accumulation models with migration models.  相似文献   

Microseismic activity in the Hellenic Volcanic Arc, Greece, with emphasis on the seismotectonic setting of the Santorini–Amorgos zone     

Marco Bohnhoff  Martina Rische  Thomas Meier  Dirk Becker  George Stavrakakis  Hans-Peter Harjes 《Tectonophysics》2006,423(1-4):17

The volcanic arc of the Hellenic subduction zone with its four volcanic centers is of major relevance when evaluating the seismovolcanic hazard for the Aegean region. We present results from a 22-station temporary seismic network (CYCNET) in the central Hellenic Volcanic Arc (HVA). CYCNET recordings allow to analyze the level and spatio-temporal evolution of microseismic activity in this region for the first time. A total of 2175 events recorded between September 2002 and July 2004 are analyzed using statistical methods, cluster analysis and relative relocation techniques. We identify distinct regions with significantly varying spatio-temporal behavior of microseismicity. A large portion of the seismic activity within the upper crust is associated with the presence of islands representing horst structures that were generated during the major Oligocene extensional phase. In contrast, the central part of the Cyclades metamorphic core complex remains aseismic considering our magnitude threshold of 1.8 except one spot where events occur swarm-like and with highly similar waveforms.The highest activity in the study area was identified along the SW–NE striking Santorini–Amorgos zone. Within this zone the submarine Columbo volcano exhibits strong temporal variations of seismic activity on a high background level. This activity is interpreted to be directly linked to the magma reservoir and therein the migration of magma and fluids towards the surface. NE of Columbo where no volcanic activity has yet been reported we observe a similar seismicity pattern with small-scaled activity spots that might represent local pathways of upward migrating fluids or even developing volcanic activity within this zone of crustal weakness. In contrast, the Santorini and Milos volcanic complexes do not show significant temporal variations and low to moderate background activity, respectively. Relating our results to the distribution of historical earthquakes and the GPS-derived horizontal velocity field we conclude that the Santorini–Amorgos zone is presently in the state of right-lateral transtension reflecting a major structural boundary of the volcanic arc subdividing it into a seismically and volcanically quiet western and an active eastern part.  相似文献   

Modelling of Rayleigh-type seam waves in disturbed coal seams and around a coal mine roadway   总被引：3，自引：0，他引：3  

Katja Essen  Thomas Bohlen  Wolfgang Friederich  Thomas Meier 《Geophysical Journal International》2007,170(2):511-526

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