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991.
J. Heintze P. Lennert S. Polenz B. Schmidt J. Spitzer W. Brückner W. Hofmann B. Povh 《Experimental Astronomy》1989,1(1):21-34
According to a proposal of Lloyd-Evans (1985), the average charge of particles in the cosmic radiation near 1014eV can be determined by observing the effect of the solar magnetic field on the Sun's shadow in the angular distribution of energetic primary cosmic ray particles. This suggestion is shown to be realizable with a new type of EAS-array proposed for the purpose of high energy -ray astronomy. The same measurement provides information on the integrated strength of the solar magnetic field. As the array will be sensitive and provide good angular resolution down to a few times 1012eV, more detailed results on the primary composition near 1013eV can be obtained by investigating the shape of the shadow of the Moon as affected by the geomagnetic field. 相似文献
992.
Monsoon-induced upwelling off the Vietnamese coast 总被引:1,自引:0,他引:1
Joachim W. Dippner Kim Vinh Nguyen Hartmut Hein Thomas Ohde Natalie Loick 《Ocean Dynamics》2007,57(1):46-62
During the southwest monsoon from July 8 to 28, 2003, an interdisciplinary cruise took place in the central area of Vietnamese upwelling with “MV Nghien Cuu Bien” in the South China Sea. Physical observations in the upwelling area are analyzed with respect to local/regional wind forcing and far field forcing. Nutrients and phytoplankton measurements are discussed with respect to exchange processes between different water masses. The wind-induced coastal upwelling by local wind forcing is much weaker than in the previous years due to weaker-than-normal winds. This can be attributed to the far field forcing of the 2002/2003 El Niño event which modulates the upwelling intensity. The atmospheric conditions reflect the typical situation after an El Niño event which weakens the wind-induced coastal upwelling, reduces the latent heat flux, and results in higher-than-normal sea-surface temperatures. The general circulation pattern during SW monsoon is driven by the spatial asymmetry in the monsoon forcing. The flow pattern is characterized by an upwelling-induced northward undercurrent and a recently detected southward countercurrent. The resulting stretching deformation of this flow pattern forms an offshore jet between ~12°N and 12.5°N and causes a local enhancement of the upwelling intensity. The upwelling due to stretching deformation is a peculiarity, which makes the Vietnamese upwelling area different to other upwelling areas. A budget of the upwelling components is presented: the strongest contribution in 2003 to the Vietnamese upwelling is the dynamical upwelling due to the clockwise rotation of the northward undercurrent. The internal radius of deformation separates the upwelling area from the offshore area as well as different water masses. Mekong River and the Gulf of Thailand waters which are offshore show nutrient depletion. Therefore, high chlorophyll maxima cannot be explained by nutrient supply from river runoff. The dynamical upwelling brings in nutrient-rich Maximum Salinity Water into the euphotic zone. This causes a subsurface chlorophyll maximum between 20 and 40 m water depth along the northward undercurrent. Deflection from the Redfield ratio in the C:N ratio and negative excess nitrogen identifies the region as nitrogen-limited which may favor cyanobacteria blooms. The consequence is a unique feature in new production: in the upwelling area, new production is based on upwelled nitrate, whereas offshore in the nutrient-depleted Mekong and Gulf of Thailand water, new production is based in addition on nitrogen fixation. 相似文献
993.
J. Hansen M. Sato R. Ruedy P. Kharecha A. Lacis R. Miller L. Nazarenko K. Lo G. A. Schmidt G. Russell I. Aleinov S. Bauer E. Baum B. Cairns V. Canuto M. Chandler Y. Cheng A. Cohen A. Del Genio G. Faluvegi E. Fleming A. Friend T. Hall C. Jackman J. Jonas M. Kelley N. Y. Kiang D. Koch G. Labow J. Lerner S. Menon T. Novakov V. Oinas Ja. Perlwitz Ju. Perlwitz D. Rind A. Romanou R. Schmunk D. Shindell P. Stone S. Sun D. Streets N. Tausnev D. Thresher N. Unger M. Yao S. Zhang 《Climate Dynamics》2007,29(7-8):661-696
We carry out climate simulations for 1880–2003 with GISS modelE driven by ten measured or estimated climate forcings. An ensemble
of climate model runs is carried out for each forcing acting individually and for all forcing mechanisms acting together.
We compare side-by-side simulated climate change for each forcing, all forcings, observations, unforced variability among
model ensemble members, and, if available, observed variability. Discrepancies between observations and simulations with all
forcings are due to model deficiencies, inaccurate or incomplete forcings, and imperfect observations. Although there are
notable discrepancies between model and observations, the fidelity is sufficient to encourage use of the model for simulations
of future climate change. By using a fixed well-documented model and accurately defining the 1880–2003 forcings, we aim to
provide a benchmark against which the effect of improvements in the model, climate forcings, and observations can be tested.
Principal model deficiencies include unrealistically weak tropical El Nino-like variability and a poor distribution of sea
ice, with too much sea ice in the Northern Hemisphere and too little in the Southern Hemisphere. Greatest uncertainties in
the forcings are the temporal and spatial variations of anthropogenic aerosols and their indirect effects on clouds.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
994.
Statistical analysis of spatial point patterns on deep seismic reflection data: a preliminary test 总被引:1,自引:0,他引:1
K. Vasudevan S. Eckel F. Fleischer V. Schmidt F.A. Cook 《Geophysical Journal International》2007,171(2):823-840
Spatial point patterns generated from bitmaps of images of processed reflection seismic profiles are analysed to quantify the reflectivity patterns. The point process characteristics for two different regions of a deep seismic reflection profile in northwestern Canada demonstrate that in both cases the points are not randomly distributed and that the point pattern distribution is different between the regions. The cluster effects for small point pair distances are stronger for the region of data where there is strong sedimentary layering than for the region where the layering is less distinct. As a result, it appears that future developments in point pattern analysis may provide a new tool for analysing spatial variations in reflection data. 相似文献
995.
Impact of partial steps and momentum advection schemes in a global ocean circulation model at eddy-permitting resolution 总被引:4,自引:6,他引:4
Barnier Bernard Gurvan Madec Thierry Penduff Jean-Marc Molines Anne-Marie Treguier Julien Le Sommer Aike Beckmann Arne Biastoch Claus Böning Joachim Dengg Corine Derval Edmée Durand Sergei Gulev Elizabeth Remy Claude Talandier Sébastien Theetten Mathew Maltrud Julie McClean Beverly De Cuevas 《Ocean Dynamics》2006,56(5-6):543-567
Series of sensitivity tests were performed with a z-coordinate, global eddy-permitting (1/4°) ocean/sea-ice model (the ORCA-R025 model configuration developed for the DRAKKAR project) to carefully evaluate the impact of recent state-of-the-art numerical schemes on model solutions. The combination of an energy–enstrophy conserving (EEN) scheme for momentum advection with a partial step (PS) representation of the bottom topography yields significant improvements in the mean circulation. Well known biases in the representation of western boundary currents, such as in the Atlantic the detachment of the Gulf Stream, the path of the North Atlantic Current, the location of the Confluence, and the strength of the Zapiola Eddy in the south Atlantic, are partly corrected. Similar improvements are found in the Pacific, Indian, and Southern Oceans, and characteristics of the mean flow are generally much closer to observations. Comparisons with other state-of-the-art models show that the ORCA-R025 configuration generally performs better at similar resolution. In addition, the model solution is often comparable to solutions obtained at 1/6 or 1/10° resolution in some aspects concerning mean flow patterns and distribution of eddy kinetic energy. Although the reasons for these improvements are not analyzed in detail in this paper, evidence is shown that the combination of EEN with PS reduces numerical noise near the bottom, which is likely to affect current–topography interactions in a systematic way. We conclude that significant corrections of the mean biases presently seen in general circulation model solutions at eddy-permitting resolution can still be expected from the development of numerical methods, which represent an alternative to increasing resolution. 相似文献
996.
Guido L. B. Wiesenberg Jan Schwarzbauer Michael W. I. Schmidt Lorenz Schwark 《Organic Geochemistry》2004,35(11-12):1371
Agricultural soils are regarded as one potential sink for atmospheric CO2 via photosynthetic fixation in plant biomass and subsequent transformation into soil organic matter upon soil diagenesis. The difference in C-isotope signatures of C3- vs. C4-plants allows for a natural isotopic labelling of soil organic matter after changes from C3- to C4-cropping. In this study, we demonstrate that isotopic shifts are paralleled by molecular signatures of C3- vs. C4-crop alkyl lipids. Turnover times vary significantly, based on cropping techniques. For grain-maize cropped soils at steady state average turnover times of 40 years for bulk SOC, 35 years for n-alkanes and 21 years for n-carboxylic acids were determined. Turnover times for silage-maize cropped soil at steady state were on average 250 years for bulk SOC, 60 years for n-alkanes and 49 years for n-carboxylic acids. Turnover times reported here for silage-maize cropped soils may be taken as maximum values only, because they derive from a single trial, which was affected by addition of anthropogenic refractory carbon. Discrimination of input from various plant parts (roots, stems and leaves) based on bulk C-isotopes is not feasible but can easily be achieved using compositions of carboxylic acids, especially the ratio of n-C24 vs. n-C22+26 and their respective C-isotope values. This enables delineation of the influence of different cropping techniques, e.g., silage- or grain-maize, on carbon storage in soils. Admixture of external sources of organic matter to the soil organic carbon pool of an urban site in Halle, Germany was identified based on alkyl lipid distributions. Nearby lignite mining was identified as a source for non-crop-derived alkyl lipids, primarily based on the elevated n-C26-carboxylic acid content and heavier carbon isotopic signatures. 相似文献
997.
Diatom-based conductivity and water-level inference models from eastern Tibetan (Qinghai-Xizang) Plateau lakes 总被引:7,自引:0,他引:7
Xiangdong Yang Christian Kamenik Roland Schmidt Sumin Wang 《Journal of Paleolimnology》2003,30(1):1-19
Climate in central Asia is dominated by the Asian monsoon. The varying impact of the summer monsoon across the Tibetan (Qinghai-Xizang) Plateau provides a strong gradient in precipitation, resulting in lakes of different salinity. Diatoms have been shown to indicate changes in salinity. Thus, transfer functions for diatoms and salinity or related environmental variables represent an excellent tool for paleoclimatic reconstructions in the Tibetan Plateau. Forty freshwater to hypersaline lakes (salinity: 0.1 to 91.7 g l–1) were investigated in the eastern Tibetan Plateau. The relationship between 120 diatom taxa and conductivity, maximum water depth and major ions were analyzed using an indicator value approach, ordination and taxon response models. Canonical correspondence analysis indicated that conductivity was the most important variable, accounting for 10.8% of the variance in the diatom assemblages. In addition water depth and weathering were influential. Weighted Averaging (WA) and Weighted Averaging Partial Least Square (WA-PLS) regression and calibration models were used to establish diatom-conductivity and water depth transfer functions. An optimal two-component WA-PLS model provided a high jack-knifed coefficient of prediction for conductivity (r2
jack = 0.92), with a moderate root mean squared error of prediction (RMSEPjack = 0.22), a very low mean bias (0.0003), and a moderate maximum bias (0.26). A WA model with tolerance downweighting resulted in a slightly lower r2
jack (0.89) for water depth, with RMSEPjack= 0.26, mean bias = –0.0103 and maximum bias = 0.26. 相似文献
998.
999.
Scattering parameters of the lithosphere below the Massif Central, France, from teleseismic wavefield records 总被引:1,自引:0,他引:1
Joachim R. R. Ritter Sergei A. Shapiro & Barbara Schechinger 《Geophysical Journal International》1998,134(1):187-198
Teleseismic P -wave recordings are analysed in the frequency range 0.3–6 Hz to derive structural (statistical) parameters of the lithosphere underneath the French Massif Central. For this we analyse differences in frequency-dependent intensities of the mean wavefield and the fluctuation wavefield. It is possible to discriminate a weak fluctuation regime of the wavefield in the frequency range below 1 Hz and a strong fluctuation regime starting above 1 Hz and continuing to higher frequencies. The observed wavefield fluctuations in the frequency range 0.3–3 Hz can be explained by scattering of the teleseismic P wave front at elastic inhomogeneities in the lithosphere. A statistical distribution of the inhomogeneities is assumed and the concept of random media is applied. The lithospheric structure under the Massif Central can be described as a 70 km thick heterogeneous layer with velocity fluctuations of 3–7 per cent and correlation lengths of the heterogeneities of 1–16 km. 相似文献
1000.
A. P. Schmidt 《Journal of Geochemical Exploration》1998,62(1-3)
Over the last few years various lead precipitates have been found in natural gas production installations in north-western Europe during routine cleaning operations. We have studied the composition and morphology of these precipitates and will discuss the probable depositional processes. The lead precipitates can be divided into three categories based on morphology and composition. (1) Thin, crustal precipitates containing metallic lead, barite and galena. These precipitates originate from untreated gas–water mixtures, and are found in pipes throughout production installations. (2) Annular, homogeneous precipitates of metallic lead, formed from separated production water in pumps of production installations. (3) Suspended precipitates which are found either in the well tubing, or in pipes or valves downstream from the installations, originating from untreated gas–water mixtures. All lead precipitates contain 210Pb, whereas precipitates of both lead and barite contain 226Ra as well. These naturally occurring radionuclides are most likely derived from 238U-enriched organic sediments or 226Ra-enriched precipitates in or near the gas reservoirs. 相似文献