EDI convection measurements at 5–6 RE in the post-midnight region     

J. M. Quinn  G. Paschmann  N. Sckopke  V. K. Jordanova  H. Vaith  O. H. Bauer  W. Baumjohann  W. Fillius  G. Haerendel  S. S. Kerr  C. A. Kletzing  K. Lynch  C. E. McIlwain  R. B. Torbert  E. C. Whipple 《Annales Geophysicae》1999,17(12):1503-1512

We present the first triangulation measurements of electric fields with the electron drift instrument (EDI) on Equator-S. We show results from five high-data-rate passes of the satellite through the near-midnight equatorial region, at geocentric distances of approximately 5–6 R_E, during geomagnetically quiet conditions. In a co-rotating frame of reference, the measured electric fields have magnitudes of a few tenths of mV/m, with the E × B drift generally directed sunward but with large variations. Temporal variations of the electric field on time scales of several seconds to minutes are large compared to the average magnitude. Comparisons of the “DC” baseline of the EDI-measured electric fields with the mapped Weimer ionospheric model and the Rowland and Wygant CRRES measurements yield reasonable agreement.  相似文献   

A flux transfer event observed at the magnetopause by the Equator-S spacecraft and in the ionosphere by the CUTLASS HF radar   总被引：2，自引：0，他引：2  

D. A. Neudegg  T. K. Yeoman  S. W. H. Cowley  G. Provan  G. Haerendel  W. Baumjohann  U. Auster  K.-H. Fornacon  E. Georgescu  C. J. Owen 《Annales Geophysicae》1999,17(6):707-711

Observations of a flux transfer event (FTE) have been made simultaneously by the Equator-S spacecraft near the dayside magnetopause whilst corresponding transient plasma flows were seen in the near-conjugate polar ionosphere by the CUTLASS Finland HF radar. Prior to the occurrence of the FTE, the magnetometer on the WIND spacecraft ≈226 R_E upstream of the Earth in the solar wind detected a southward turning of the interplanetary magnetic field (IMF) which is estimated to have reached the subsolar magnetopause ≈77 min later. Shortly afterwards the Equator-S magnetometer observed a typical bipolar FTE signature in the magnetic field component normal to the magnetopause, just inside the magnetosphere. Almost simultaneously the CUTLASS Finland radar observed a strong transient flow in the F region plasma between 78° and 83° magnetic latitude, near the ionospheric region predicted to map along geomagnetic field lines to the spacecraft. The flow signature (and the data set as a whole) is found to be fully consistent with the view that the FTE was formed by a burst of magnetopause reconnection.  相似文献   

Design considerations for using Distributed Acoustic Sensing for cross-well seismics: A case study for CO2 storage     

Andreas Wuestefeld  Wolfgang Weinzierl 《Geophysical Prospecting》2020,68(6):1893-1905

Downhole monitoring with fibre-optic Distributed Acoustic Sensing (DAS) systems offers unprecedented spatial resolution. At the same time, costs are reduced since repeated wireline surveys can be replaced by the permanent installation of comparatively cheap fibre cables. However, the single component nature of fibre data requires novel approaches when designing a monitoring project such as cross-well seismics. At the example of the shallow CO₂ injection test site in Svelvik, Norway, we model the evolution of velocity changes during CO₂ injection based on rock physics theory. Different cross-well seismic design scenarios are then considered to evaluate the best design and the limits of this method to detect containment breach. We present a series of evaluation tools to compare the effect of different well spacings for cross-well seismic tomography. In addition to travel-times, we also consider characteristic amplitude changes along the fibre unique to DAS strain measurements, which might add a constraint to the inversion. We also compare the effect of using helical fibres instead of classical straight fibres. We thus present a toolbox to evaluate and compare different monitoring design options for fibre optic downhole installations for cross-well monitoring.  相似文献   

洪水风险=灾害事件×暴露程度×脆弱程度   总被引：2，自引：0，他引：2  

Wolfgang KRON 《湖泊科学》2003,15(Z1):190-204

世界上,洪水可能是造成损失最大的自然灾害.世界上没有哪个地区不受到洪水的威助、由于洪灾风险是灾害事件、洪泛区财产遭遇风险的程度,以及它们的脆弱性的函数,所以灾害损失的增长与上述各个方面的变化都有关.防洪措施可以减少灾害事件的频率,恰当的预防措施也能显著降低财产风险.然而除了公共措施和私人措施外,在减少私人、企业、甚至整个社会的风险方面,保险发挥着关键作用.近年来,对洪水保险的需求日益增长,促使保险公司必须采取适当的解决方案.与此同时,至关重要的是,保险公司应当清楚在极端情况下他们自己可能承担的最大损失.  相似文献   

Physical laboratory analyses of intergravel flow through brown trout redds (Salmo trutta fario) in response to coarse sand infiltration          下载免费PDF全文

Wolfgang Obruca  Christoph Hauer 《地球表面变化过程与地形》2017,42(4):670-680

In the spawning environment of salmonids, the quality of the intergravel flow is an essential abiotic requirement for the survival success of incubated embryos. As one of the most frequently investigated anthropogenic environmental impacts, the enhanced mobilization of fine sediments (<1 mm) and their entry into riverine ecosystems is considered as a major cause for the degradation of a variety of biological processes and habitats, including the spawning habitats of salmonids. In catchments draining crystalline bedrock, however, like the Bohemian Massif in the northern part of Austria, the excessive loading of river channels with coarse sand and fine gravel sediments (D = 1–10 mm) and less cohesive than fines is common as a consequence of altered catchment land use. Here, far less understanding exists of the mechanism and the possible implications of coarse sand infiltration on the functioning of the intergravel flow in salmonid redds. To investigate the intergravel flow hydraulics in response to coarse sand infiltration (D₅₀ = 2 mm) in brown trout spawning redds (Salmo trutta fario ) under controlled conditions, a laboratory flume experiment with three infiltration scenarios was conducted: (1) no infiltration; (2) segmental infiltration; and (3) full section infiltration. A more than two times drop in the average intergravel flow velocity was documented from scenario 1 (5.85 cms^?1) to scenario 2 (2.53 cms^?1) and another clear reduction was seen from scenario 2 (2.53 cms^?1) to scenario 3 (1.61 cms^?1). Moreover, in scenario 3, a clear reduction of the intergravel flow distance traveled was observed. Based on the findings we conclude that future considerations regarding the sustainable catchment management of salmonid fisheries should include programs to reduce not only the excessive entry of fines, but, in the relevant catchments, also the entry of excessive coarse sand into the riverine ecosystem. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Distribution of throughfall and stemflow in multi‐strata agroforestry,perennial monoculture,fallow and primary forest in central Amazonia,Brazil     

Gtz Schroth  Luciana Ferreira Da Silva  Marc‐Andree Wolf  Wenceslau Geraldes Teixeira  Wolfgang Zech 《水文研究》1999,13(10):1423-1436

The partitioning of rain water into throughfall, stemflow and interception loss when passing through plant canopies depends on properties of the respective plant species, such as leaf area and branch angles. In heterogeneous vegetation, such as tropical forest or polycultural systems, the presence of different plant species may consequently result in a mosaic of situations with respect to quantity and quality of water inputs into the soil. As these processes influence not only the water availability for the plants, but also water infiltration and nutrient leaching, the understanding of plant effects on the repartitioning of rain water may help in the optimization of land use systems and management practices. We measured throughfall and stemflow in a perennial polyculture (multi‐strata agroforestry), monocultures of peach palm (Bactris gasipaes) for fruit and for palmito, a monoculture of cupuaçu (Theobroma grandiflorum), spontaneous fallow and primary forest during one year in central Amazonia, Brazil. The effect on rain water partitioning was measured separately for four useful tree species in the polyculture and for two tree species in the primary forest. Throughfall at two stem distances, and stemflow, differed significantly between tree species, resulting in pronounced spatial patterns of water input into the soil in the polyculture system. For two tree species, peach palm for fruit (Bactris gasipaes) and Brazil nut trees (Bertholletia excelsa), the water input into the soil near the stem was significantly higher than the open‐area rainfall. This could lead to increased nutrient leaching when fertilizer is applied close to the stem of these trees. In the primary forest, such spatial patterns could also be detected, with significantly higher water input near a palm (Oenocarpus bacaba) than near a dicotyledonous tree species (Eschweilera sp.). Interception losses were 6·4% in the polyculture, 13·9 and 12·3% in the peach palm monocultures for fruit and for palmito, respectively, 0·5% in the cupuaçu monoculture and 3·1% in the fallow. With more than 20% of the open‐area rainfall, the highest stemflow contributions to the water input into the soil were measured in the palm monocultures and in the fallow. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

V. Lakshmikantham,S. Leela,A. A. Martynyuk: Stability Analysis of Nonlinear Systems. Marcel Dekker Inc., ISBN: 0-8247-8067-1     

Wolfgang Jansen 《Astronomische Nachrichten》1995,316(1):67-67

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Scientific detector workshop 2022 on-sky performance verification of near-infrared e−APD technology for wavefront sensing and demonstration of e−APD pixel performance to improve the sensitivity of large science focal planes     

Gert Finger  Frank Eisenhauer  Reinhard Genzel  Christopher Mandla  Ian Baker  Domingo Alvarez  Antonio Amorim  Wolfgang Brandner  Christophe Dupuy  Casey Deen  Derek Ives  Leander Mehrgan  Manfred Meyer  Karin Perraut  Guy Perrin  Jörg Stegmeier  Christian Straubmeier  Harald J. Weller  Vincent Isgar 《Astronomische Nachrichten》2023,344(8-9):e20230069

Near-infrared adaptive optics as well as fringe tracking for coherent beam combination in optical interferometry require the development of high-speed sensors. Because of the high speed, a large analog bandwidth is required. The short exposure times result in small signal levels which require noiseless detection. Both requirements cannot be met by state-of-the-art conventional CMOS technology of near-infrared arrays as has been attempted previously. A total of five near-infrared SAPHIRA 320 × 256 pixel HgCdTe e⁻APD arrays have been deployed in the wavefront sensors and in the fringe tracker of the VLTI instrument GRAVITY. The current limiting magnitude for coherent exposures with GRAVITY is m_k = 19, which is made possible with ADP technology. New avalanche photo-diode array (APD) developments since GRAVITY include the extension of the spectral sensitivity to the wavelength range from 0.8 to 2.5 μm. After GRAVITY a larger format array with 512 × 512 pixels has been developed for both AO applications at the ELT and for long integration times. Since dark currents of <10⁻³ e⁻/s have been demonstrated with 1Kx1K e⁻APD arrays and 2Kx2K e⁻APD arrays have already been developed, the possibilities and adaptations of e⁻APD technology to provide noiseless large-format science-grade arrays for long integration times are also discussed.  相似文献