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181.
Yaniv Y. Munwes Stefan Geyer David Katoshevski Danny Ionescu Tobias Licha Christian Lott Jonathan B. Laronne Christian Siebert 《水文研究》2020,34(2):455-472
The Dead Sea is a closed lake, the water level of which is lowering at an alarming rate of about 1 m/year. Factors difficult to determine in its water balance are evaporation and groundwater inflow, some of which emanate as submarine groundwater discharge. A vertical buoyant jet generated by the difference in densities between the groundwater and the Dead Sea brine forms at submarine spring outlets. To characterize this flow field and to determine its volumetric discharge, a system was developed to measure the velocity and density of the ascending submarine groundwater across the center of the stream along several horizontal sections and equidistant depths while divers sampled the spring. This was also undertaken on an artificial submarine spring with a known discharge to determine the quality of the measurements and the accuracy of the method. The underwater widening of the flow is linear and independent of the volumetric spring discharge. The temperature of the Dead Sea brine at lower layers primarily determines the temperature of the surface of the upwelling, produced above the jet flow, as the origin of the main mass of water in the submarine jet flow is Dead Sea brine. Based on the measurements, a model is presented to evaluate the distribution of velocity and solute density in the flow field of an emanating buoyant jet. This model allows the calculation of the volumetric submarine discharge, merely requiring either the maximum flow velocity or the minimal density at a given depth. 相似文献
182.
Jean-Pierre Lebreton Athena Coustenis Jonathan Lunine François Raulin Tobias Owen Darrell Strobel 《Astronomy and Astrophysics Review》2009,17(2):149-179
The Cassini–Huygens mission, comprising the NASA Saturn Orbiter and the ESA Huygens Probe, arrived at Saturn in late June
2004. The Huygens probe descended under parachute in Titan’s atmosphere on 14 January 2005, 3 weeks after separation from
the Orbiter. We discuss here the breakthroughs that the Huygens probe, in conjunction with the Cassini spacecraft, brought
to Titan science. We review the achievements ESA’s Huygens probe put forward and the context in which it operated. The findings
include new localized information on several aspects of Titan science: the atmospheric structure and chemical composition;
the aerosols distribution and content; the surface morphology and composition at the probe’s landing site; the winds, the
electrical properties, and the implications on the origin and evolution of the satellite. 相似文献
183.
J. Maarten de Moor Tobias P. Fischer Erik H. Hauri Viorel Atudorei 《Geochimica et cosmochimica acta》2010,74(18):5382-5397
Sulfur isotope compositions of pumice and adsorbed volatiles on ash from the first historical eruption of Anatahan volcano (Mariana arc) are presented in order to constrain the sources of sulfur erupted during the period 10-21 May, 2003. The isotopic composition of S extracted from erupted pumice has a narrow range, from δ34SV-CDT +2.6‰ to +3.2‰, while the composition of sulfur adsorbed onto ash has a larger range (+2.8‰ to +5.3‰). Fractionation modeling for closed and open system scenarios suggests that degassing of SO2 raised the δ34SV-CDT value of S dissolved in the melt from an initial composition of between +1.6‰ and +2.6‰ for closed-system degassing, or between −0.5‰ and +1.5‰ for open-system degassing, however closed-system degassing is the preferred model. The calculated values for the initial composition of the magma represent a MORB-like (δ34SV-CDT ∼ 0‰) mantle source with limited contamination by subducted seawater sulfate (δ34SV-CDT +21‰). Modeling also suggests that the δ34SV-CDT value of SO2 gas in closed-system equilibrium with the degassed magma was between +0.9‰ and +2.5‰. The δ34SV-CDT value of sulfate adsorbed onto ash in the eruption plume (+2.8‰ to +5.1‰) is consistent with sulfate formation by oxidation of magmatic SO2 in the eruption column. The sulfur isotope composition of sulfate adsorbed to ash changes from lower δ34S values for ash erupted early in the eruption to higher δ34S values for ash erupted later in the eruption. We interpret the temporal/stratigraphic change in sulfate isotopic composition to primarily reflect a change in the isotopic composition of magmatic SO2 released from the progressively degassing magma and is attributed to the expulsion of an accumulated gas phase at the beginning of the eruption. More efficient oxidation of magmatic SO2 gas to sulfate in the early water-rich eruption plume probably contributed to the change in S isotope compositions observed in the ash leachates. 相似文献
184.
185.
186.
Kamil Teke Johannes B?hm Tobias Nilsson Harald Schuh Peter Steigenberger Rolf Dach Robert Heinkelmann Pascal Willis R��diger Haas Susana Garc��a-Espada Thomas Hobiger Ryuichi Ichikawa Shingo Shimizu 《Journal of Geodesy》2011,85(7):395-413
CONT08 was a 15 days campaign of continuous Very Long Baseline Interferometry (VLBI) sessions during the second half of August 2008 carried out by the International VLBI Service for Geodesy and Astrometry (IVS). In this study, VLBI estimates of troposphere zenith total delays (ZTD) and gradients during CONT08 were compared with those derived from observations with the Global Positioning System (GPS), Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), and water vapor radiometers (WVR) co-located with the VLBI radio telescopes. Similar geophysical models were used for the analysis of the space geodetic data, whereas the parameterization for the least-squares adjustment of the space geodetic techniques was optimized for each technique. In addition to space geodetic techniques and WVR, ZTD and gradients from numerical weather models (NWM) were used from the European Centre for Medium-Range Weather Forecasts (ECMWF) (all sites), the Japan Meteorological Agency (JMA) and Cloud Resolving Storm Simulator (CReSS) (Tsukuba), and the High Resolution Limited Area Model (HIRLAM) (European sites). Biases, standard deviations, and correlation coefficients were computed between the troposphere estimates of the various techniques for all eleven CONT08 co-located sites. ZTD from space geodetic techniques generally agree at the sub-centimetre level during CONT08, and??as expected??the best agreement is found for intra-technique comparisons: between the Vienna VLBI Software and the combined IVS solutions as well as between the Center for Orbit Determination (CODE) solution and an IGS PPP time series; both intra-technique comparisons are with standard deviations of about 3?C6?mm. The best inter space geodetic technique agreement of ZTD during CONT08 is found between the combined IVS and the IGS solutions with a mean standard deviation of about 6?mm over all sites, whereas the agreement with numerical weather models is between 6 and 20?mm. The standard deviations are generally larger at low latitude sites because of higher humidity, and the latter is also the reason why the standard deviations are larger at northern hemisphere stations during CONT08 in comparison to CONT02 which was observed in October 2002. The assessment of the troposphere gradients from the different techniques is not as clear because of different time intervals, different estimation properties, or different observables. However, the best inter-technique agreement is found between the IVS combined gradients and the GPS solutions with standard deviations between 0.2 and 0.7?mm. 相似文献
187.
Regional frequency analysis of rainfall extremes in Southern Malawi using the index rainfall and L-moments approaches 总被引:3,自引:1,他引:2
Cosmo S. Ngongondo Chong-Yu Xu Lena M. Tallaksen Berhanu Alemaw Tobias Chirwa 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(7):939-955
Rainfall extremes often result in the occurrence of flood events with associated loss of life and infrastructure in Malawi.
However, an understanding of the frequency of occurrence of such extreme events either for design or disaster planning purposes
is often limited by data availability at the desired temporal and spatial scales. Regionalisation, which involves “trading
time for space” by pooling together observations for stations with similar behavior, is an alternative approach for more accurate
determination of extreme events even at ungauged areas or sites with short records. In this study, regional frequency analysis
of rainfall extremes in Southern Malawi, large parts of which are flood prone, was undertaken. Observed 1-, 3-, 5- and 7-day
annual maximum rainfall series for the period 1978–2007 at 23 selected rainfall stations in Southern Malawi were analysed.
Cluster analysis using scaled at-site characteristics was used to determine homogeneous rainfall regions. L-moments were applied
to derive regional index rainfall quantiles. The procedure also validated the three rainfall regions identified through homogeneity
and heterogeneity tests based on Monte Carlo simulations with regional average L-moment ratios fitted to the Kappa distribution.
Based on assessments of the accuracy of the derived index rainfall quantiles, it was concluded that the performance of this
regional approach was satisfactory when validated for sites not included in the sample data. The study provides an estimate
of the regional characteristics of rainfall extremes that can be useful in among others flood mitigation and engineering design. 相似文献
188.
Urban and rural limestone weathering; the contribution of dust to black crust formation 总被引:2,自引:2,他引:0
Ákos Török Tobias Licha Klaus Simon Siegfried Siegesmund 《Environmental Earth Sciences》2011,63(4):675-693
A novel approach of studying dust, black crust and host limestones by using various techniques is presented in this paper.
Samples were collected from limestone monuments located in rural, urban and industrial areas in Germany and Hungary. The paper
focuses on differences in the mineralogical composition, major and trace element distribution of materials and their total
polyaromatic hydrocarbons (PAH) concentration having different exposure to air pollutants. High concentration of gypsum was
found in laminar and dendritic black crusts and even in the dust of both urban and rural areas, despite the low concentration
of SO2 in rural atmospheric environments. The black crusts show a typical microfabric with distinct layers of various gypsum–calcite
mineral associations, silt-sized mineral fragments and black particle content. In dust, newly formed gypsum crystals were
found along with mineral fragments, and siliceous and, less frequently, carbonaceous fly ash particles. High concentration
of lead was found both in the samples of urban and rural areas of Germany and Hungary. Lead mostly accumulates in dust and
also in the black crust. Highest lead concentrations were found not on the surface of the black crust, but close to the crust/limestone
boundary according to LA-ICPMS analyses. It indicates that despite the ban of leaded petrol, lead is still present in the
dust and the in the soiled zones of the built environment. Similarly to lead, no significant difference in the total PAH content
of dust and crust samples were found in the two countries. Dusts are equally enriched in PAH in both countries, whereas black
crusts contain fewer amounts. Most of the aqueous extracts of the samples were saturated with respect to sulphate, which also
indicate the presence of gypsum, whilst in some German samples unsaturated conditions were detected. In summary, by using
a combination of these analytical techniques, it was possible to distinguish rural and urban samples and to outline the role
of dust in bringing pollutants to the stone surface. It is suggested that the analysed dust and stone samples indicate not
only present, but also the past, pollution fluxes and as a consequence stones similar to sediments or surface waters can be
used as environment indicators. 相似文献
189.
In this study the observed non-linearity in the spatial pattern and time evolution of El Niño Southern Oscillation (ENSO) events is analyzed. It is shown that ENSO skewness is not only a characteristic of the amplitude of events (El Niños being stronger than La Niñas) but also of the spatial pattern and time evolution. It is demonstrated that these non-linearities can be related to the non-linear response of the zonal winds to sea surface temperature (SST) anomalies. It is shown in observations as well as in coupled model simulations that significant differences in the spatial pattern between positive (El Niño) versus negative (La Niña) and strong versus weak events exist, which is mostly describing the difference between central and east Pacific events. Central Pacific events tend to be weak El Niño or strong La Niña events. In turn east Pacific events tend to be strong El Niño or weak La Niña events. A rotation of the two leading empirical orthogonal function modes illustrates that for both El Niño and La Niña extreme events are more likely than expected from a normal distribution. The Bjerknes feedbacks and time evolution of strong ENSO events in observations as well as in coupled model simulations also show strong asymmetries, with strong El Niños being forced more strongly by zonal wind than by thermocline depth anomalies and are followed by La Niña events. In turn strong La Niña events are preceded by El Niño events and are more strongly forced by thermocline depth anomalies than by wind anomalies. Further, the zonal wind response to sea surface temperature anomalies during strong El Niño events is stronger and shifted to the east relative to strong La Niña events, supporting the eastward shifted El Niño pattern and the asymmetric time evolution. Based on the simplified hybrid coupled RECHOZ model of ENSO it can be shown that the non-linear zonal wind response to SST anomalies causes the asymmetric forcings of ENSO events. This also implies that strong El Niños are mostly wind driven and less predictable and strong La Niñas are mostly thermocline depth driven and better predictable, which is demonstrated by a set of 100 perfect model forecast ensembles. 相似文献
190.
Tobias E. Bauer Pietari Skyttä Tobias Hermansson Rodney L. Allen Pär Weihed 《Mineralium Deposita》2014,49(5):555-573
The Skellefte district in northern Sweden is host to abundant volcanogenic massive sulphide (VMS) deposits comprising pyritic, massive, semi-massive and disseminated Zn–Cu–Au ± Pb ores surrounded by disseminated pyrite and with or without stockwork mineralisation. The VMS deposits are associated with Palaeoproterozoic upper crustal extension (D1) that resulted in the development of normal faults and related transfer faults. The VMS ores formed as sub-seafloor replacement in both felsic volcaniclastic and sedimentary rocks and partly as exhalative deposits within the uppermost part of the volcanic stratigraphy. Subsequently, the district was subjected to deformation (D2) during crustal shortening. Comparing the distribution of VMS deposits with the regional fault pattern reveals a close spatial relationship of VMS deposits to the faults that formed during crustal extension (D1) utilising the syn-extensional faults as fluid conduits. Analysing the shape and orientation of VMS ore bodies shows how their deformation pattern mimics those of the hosting structures and results from the overprinting D2 deformation. Furthermore, regional structural transitions are imitated in the deformation patterns of the ore bodies. Plotting the aspect ratios of VMS ore bodies and the comparison with undeformed equivalents in the Hokuroko district, Japan allow an estimation of apparent strain and show correlation with the D2 deformation intensity of the certain structural domains. A comparison of the size of VMS deposits with their location shows that the smallest deposits are not related to known high-strain zones and the largest deposits are associated with regional-scale high-strain zones. The comparison of distribution and size with the pattern of high-strain zones provides an important tool for regional-scale mineral exploration in the Skellefte district, whereas the analysis of ore body shape and orientation can aid near-mine exploration activities. 相似文献