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121.
Michael Engel Simon Mischel Sabrina Quanz Sven Frei Dirk Radny Rike Voelpel Axel Schmidt 《水文研究》2024,38(5):e15118
Groundwater-surface water interactions (GSI) connect rivers and streams with riparian areas and the adjacent aquifer. Although these interactions exert a substantial control of quantity and quality of both groundwater and surface water, knowledge on GSI along rivers at the regional scale, particularly for inland waterways, is still limited. We investigated GSI along the river Moselle, an important federal inland waterway in Germany, by using radon and tritium to identify gaining (water flux from the aquifer to the surface water) and losing (water flux from the surface water to the aquifer) stream conditions, respectively. Gaining stream conditions were identified by continuously measuring radon along the river during boat surveys with a high spatial resolution (every 2 km) during intermediate (October 2020) and near low flow conditions (August/September 2021). The tritium concentrations in surface water and groundwater and the resulting tritium inventories were used to characterize losing stream conditions Monthly tritium inventories from 2017 to 2022 revealed a mean loss for the whole period of 20.3 % and a mean gain of 21.8%. Both were probably triggered by a combination of losing stream conditions and flood-induced mass transfer of water from the aquifer back into the river as well as discharge fluctuations. At the investigated site Lehmen there were direct indications of an influence of surface water due to elevated tritium concentrations in the groundwater (up to 13.3 Bq L−1). Using radon mass balance modelling, good agreements of simulated versus measured radon data with respect to two groundwater end-member scenarios were obtained during intermediate flow (Spearman's ρ: 0.97 and 0.99; MAE: 10.1 and 3.4 Bq L−1) and near low flow (Spearman's ρ: 0.97 and 0.99; MAE: 11 and 6.5 Bq L−1). Considerable groundwater inflow was limited to the meander of Detzem, where cumulated groundwater inflow of about 19 m3 s−1 (9.5% of total discharge) and 4.2 m3 s−1 (3.8% of total discharge) was simulated during intermediate and near low flow, respectively. However, the groundwater inflow was relatively low compared to alpine streams, for example. The study will help to better identify and quantify GSI at the regional scale and provide methodological guidance for future studies focusing on inland waterways. 相似文献
122.
Improved UT1 predictions through low-latency VLBI observations 总被引:2,自引:2,他引:0
The quality of predictions of Earth orientation parameters (EOPs) in general, and of Universal Time (UT1) in particular, depends strongly on the time delay between the last observation available and the first prediction. Since 30 September 2007 (MJD 54373), the latency of UT1 results from a subset of single baseline VLBI observations running once per week (Mondays) has been decreased from 2 to 3 days to about 8 h. This was achieved by transmitting the raw VLBI data of 1-h duration from the observing sites in Tsukuba (Japan), Wettzell (Germany) and Ny-Ålesund (Norway) to the correlator of the Max-Planck-Institute for Radio Astronomy and the German Federal Agency of Cartography and Geodesy at Bonn, Germany, by high-speed Internet connections (e-Transfer). The reduced latency of the observations has improved the accuracy of the combined International Earth Rotation and Reference Systems Service (IERS) Rapid Service/Prediction Center (RS/PC) UT1-UTC solution by roughly 50% on the days when the data are available. Because this combination is an input to the UT1-UTC prediction process, the improved latency is also responsible for a roughly 21% improvement in the accuracy of short-term IERS RS/PC UT1-UTC predictions on the days where the data are available. 相似文献
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125.
Climate change poses formidable challenge to the development of livestock sector in India. The anticipated rise in temperature
between 2.3 and 4.8°C over the entire country together with increased precipitation resulting from climate change is likely
to aggravate the heat stress in dairy animals, adversely affecting their productive and reproductive performance, and hence
reducing the total area where high yielding dairy cattle can be economically reared. Given the vulnerability of India to rise
in sea level, the impact of increased intensity of extreme events on the livestock sector would be large and devastating for
the low-income rural areas. The predicted negative impact of climate change on Indian agriculture would also adversely affect
livestock production by aggravating the feed and fodder shortages. The livestock sector which will be a sufferer of climate
change is itself a large source of methane emissions, an important greenhouse gas. In India, although the emission rate per
animal is much lower than the developed countries, due to vast livestock population the total annual methane emissions are
about 9–10 Tg from enteric fermentation and animal wastes. 相似文献
126.
Ulf Torkelsson Gordon I. Ogilvie Axel Brandenburg James E. Pringle Åke Nordlund Robert F. Stein 《Monthly notices of the Royal Astronomical Society》2000,318(1):47-57
We excite an epicyclic motion, the amplitude of which depends on the vertical position, z , in a simulation of a turbulent accretion disc. An epicyclic motion of this kind may be caused by a warping of the disc. By studying how the epicyclic motion decays, we can obtain information about the interaction between the warp and the disc turbulence. A high-amplitude epicyclic motion decays first by exciting inertial waves through a parametric instability, but its subsequent exponential damping may be reproduced by a turbulent viscosity. We estimate the effective viscosity parameter, α v , pertaining to such a vertical shear. We also gain new information on the properties of the disc turbulence in general, and measure the usual viscosity parameter, α h , pertaining to a horizontal (Keplerian) shear. We find that, as is often assumed in theoretical studies, α v is approximately equal to α h and both are much less than unity, for the field strengths achieved in our local box calculations of turbulence. In view of the smallness (∼0.01) of α v and α h we conclude that for β p gas p mag ∼10 the time-scale for diffusion or damping of a warp is much shorter than the usual viscous time-scale. Finally, we review the astrophysical implications. 相似文献
127.
128.
A multi‐system geochronology in the Ad‐3 borehole,Pannonian Basin (Hungary) with implications for dating volcanic rocks by low‐temperature thermochronology and for interpretation of (U–Th)/He data 下载免费PDF全文
Martin Danišík László Fodor István Dunkl Axel Gerdes János Csizmeg Mária Hámor‐Vidó Noreen J. Evans 《地学学报》2015,27(4):258-269
Independent geochronological and thermal modelling approaches are applied to a biostratigraphically exceptionally well‐controlled borehole, Alcsútdoboz‐3 (Ad‐3), in order to constrain the age of Cenozoic geodynamic events in the western Pannonian Basin and to test the efficacy of the methods for dating volcanic rocks. Apatite fission track and zircon U–Pb data show two volcanic phases of Middle Eocene (43.4–39.0 Ma) and Early Oligocene (32.72 ± 0.15 Ma) age respectively. Apatite (U–Th)/He ages (23.8–14.8 Ma) and independent thermal and subsidence history models reveal a brief period of heating to 55–70 °C at ~17 Ma caused by an increased heat‐flow related to crustal thinning and mantle upwelling. Our results demonstrate that, contrary to common perception, the apatite (U–Th)/He method is likely to record ‘apparent’ or ‘mixed’ ages resulting from subsequent thermal events rather than ‘cooling’ or ‘eruption’ ages directly related to distinct geological events. It follows that a direct conversion of ‘apparent’ or ‘mixed’ (U‐Th)/He ages into cooling, exhumation or erosion rates is incorrect. 相似文献
129.
Additional aspects regarding the optimum fixed and roving sampling techniques, to those already explored in a previous authors’ throughfall study, are further investigated here. The roving technique consists in the random repositioning, with a frequency fr, of N throughfall gauges among M positions (M > N), oppositely to the fixed or stationary arrangement where N = M. Both fixed and roving optimum sampling techniques of 100 monitored throughfall events sampled with 200 fixed gauges under a semideciduous tropical rain forest in Panama were investigated by means of Monte‐Carlo numerical experiments. Mean dispersion was shown to be always smaller in the roving versus the fixed gauge arrangement, independently of the relocation frequency studied (fr = 0.1, 0.2, 0.5, 1), such that all roving schemes with N ≥ 50 gauges lay within ±5% of the mean cumulative throughfall. Results indicated that a low variability, high precision, and accuracy are obtained with a modest relocation frequency fr = 0.2 (i.e. a relocation every five episodes of the original 100 measured events) and N = 30 roving gauges, with no significant improvement worth the extra field work beyond fr > 0.2 and N >30. Only by increasing the number of roving positions from M < < 200 to M = 200, the precision and accuracy of the mean estimate were improved without comprising additional labour. Hence, a roving sampling scheme which relocates gauges over completely new fresh sites each roving cycle is recommended for future throughfall studies. Finally, we designed an a priori sampling strategy which permitted us to conclude that using only the first 20 out of the total 100 measuring events, for the remaining 80 throughfall field measurements, N = 40 roving gauges (i.e. five time less than the originally 200 gauges displayed) would have been sufficient for ensuring ≤5% error, expressed as percentage of the mean cumulative throughfall. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
130.
An early detection of the presence of rupture directivity plays a major role in the correct estimation of ground motions and
risks associated to the earthquake occurrence. We present here a simple method for a fast detection of rupture directivity,
which may be additionally used to discriminate fault and auxiliary planes and have first estimations of important kinematic
source parameters, such as rupture length and rupture time. Our method is based on the inversion of amplitude spectra from
P-wave seismograms to derive the apparent duration at each station and on the successive modelling of its azimuthal behaviour.
Synthetic waveforms are built assuming a spatial point source approximation, and the finite apparent duration of the spatial
point source is interpreted in terms of rupture directivity. Since synthetic seismograms for a point source are calculated
very quickly, the presence of directivity may be detected within few seconds, once a focal mechanism has been derived. The
method is here first tested using synthetic datasets, both for linear and planar sources, and then successfully applied to
recent Mw 6.2–6.8 shallow earthquakes in Peloponnese, Greece. The method is suitable for automated application and may be
used to improve kinematic waveform modelling approaches. 相似文献