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31.
Jeffery R. Scott Andrei P. Sokolov Peter H. Stone Mort D. Webster 《Climate Dynamics》2008,30(5):441-454
The response of the ocean’s meridional overturning circulation (MOC) to increased greenhouse gas forcing is examined using
a coupled model of intermediate complexity, including a dynamic 3-D ocean subcomponent. Parameters are the increase in CO2 forcing (with stabilization after a specified time interval) and the model’s climate sensitivity. In this model, the cessation
of deep sinking in the north “Atlantic” (hereinafter, a “collapse”), as indicated by changes in the MOC, behaves like a simple
bifurcation. The final surface air temperature (SAT) change, which is closely predicted by the product of the radiative forcing
and the climate sensitivity, determines whether a collapse occurs. The initial transient response in SAT is largely a function
of the forcing increase, with higher sensitivity runs exhibiting delayed behavior; accordingly, high CO2-low sensitivity scenarios can be assessed as a recovering or collapsing circulation shortly after stabilization, whereas
low CO2-high sensitivity scenarios require several hundred additional years to make such a determination. We also systemically examine
how the rate of forcing, for a given CO2 stabilization, affects the ocean response. In contrast with previous studies based on results using simpler ocean models,
we find that except for a narrow range of marginally stable to marginally unstable scenarios, the forcing rate has little
impact on whether the run collapses or recovers. In this narrow range, however, forcing increases on a time scale of slow
ocean advective processes results in weaker declines in overturning strength and can permit a run to recover that would otherwise
collapse. 相似文献
32.
Natalia Rudaya Pavel Tarasov Nadezhda Dorofeyuk Nadia Solovieva Ivan Kalugin Andrei Andreev Andrei Daryin Bernhard Diekmann Frank Riedel Narantsetseg Tserendash Mayke Wagner 《Quaternary Science Reviews》2009,28(5-6):540-554
This study presents the results of the palynological and diatom analyses of the sediment core recovered in Hoton-Nur Lake (48°37′18″N, 88°20′45″E, 2083 m) in 2004. Quantitative reconstruction of the Holocene vegetation and climate dynamics in the semiarid Mongolian Altai suggests that boreal woodland replaced the primarily open landscape of northwestern Mongolia at about 10 kyr BP (1 kyr = 1000 cal yr) in response to a noticeable increase in precipitation from 200–250 mm/yr to 450–550 mm/yr. A decline of the forest vegetation and a return to a predominance of open vegetation types occurred after 5 kyr BP when precipitation sums decreased to 250–300 mm/yr. Prior to 11.5 kyr BP diatom concentrations are relatively low and the lake is dominated by planktonic Cyclotella and small Fragilariaceae, suggesting the existence of a relatively deep and oligotrophic/mesotrophic lake. The great abundance of Staurosirella pinnata from the beginning of the record until 10.7 kyr BP might imply intensified erosion processes in the catchment and this is fully consistent with the presence of scarce and dry vegetation and the generally arid climate during this period. From about 10.7 kyr BP, more planktonic diatom taxa appeared and increased in abundance, indicating that the lake became more productive as diatom concentration increased. This change correlates well with the development of boreal woodland in the catchment. Decrease in precipitation and changes in the vegetation towards steppe are reflected by the rapid increase in Aulacoseira distans from about 5 kyr BP. The Holocene pollen and diatom records do not indicate soil and vegetation cover disturbances by the anthropogenic activities, implying that the main transformations of the regional vegetation occurred as a result of the natural climate change. Our reconstruction is in agreement with the paleomonsoon records from China, demonstrating an abrupt strengthening of the summer monsoon at 12 kyr BP and an associated increase in precipitation and in lake levels between 11 and 8 kyr BP, followed by the stepwise attenuation of the monsoon circulation and climate aridization towards the modern level. The records from the neighboring areas of Kazakhstan and Russia, situated west and north of Hoton-Nur, demonstrate spatially and temporally different Holocene vegetation and climate histories, indicating that the Altai Mountains as a climate boundary are of pivotal importance for the Holocene environmental and, possibly, habitation history of Central Asia. 相似文献
33.
Aurelian Andrei Radu Tatiana Angelescu Valentin Curtef Florin Delia Daniel Felea Ioana Goia Dumitru Ha?egan Bogdan Lucaschi Ancuta Manea Vlad Popa Ioan Rali?? Radu V?c?reanu 《Experimental Astronomy》2012,34(1):31-42
Around the world, several scientific projects share the interest of a global network of small Cherenkov telescopes for monitoring observations of the brightest blazars??the DWARF network. A small, ground based, imaging atmospheric Cherenkov telescope of last generation is intended to be installed and operated in Romania as a component of the DWARF network. To prepare the construction of the observatory, two support projects have been initiated. Within the framework of these projects, we have assessed a number of possible sites where to settle the observatory. In this paper we submit a brief report on the general characteristics of the best four sites selected after the local infrastructure, the nearby facilities and the social impact criteria have been applied. 相似文献
34.
An avenue to integrate theoretical, experimental and field research methods to forecast water quality in water bodies for different scenarios of water management is proposed. Exploration of the laws of organization, stability and controllability of laboratory "ideal" water microbial communities (model ecosystems) is the basis to build the following biophysical research chain:to formalize with primary field information a conceptual block-diagram of a water ecosystem →to real chemical and other density-dependent and population-growth-controlling factors → to find our limiting factors for natural ecosystems → to conduct experiments with isolated chemical factors and hydrobionts to derive kinetic dependencies and quantitative parameters→ to transfer regularities of operation and kinetic dependencies to the natural ecosystem→ retrospective verification of the model on the base of available field and derived theoretical-experimental data →prognostic calculations for the scenario. Efficiency of the approach is demonstrated in microalgal "blooming" models for Krasnoyarsk and Kantat reservoirs and in prognostication of radioecological state of great Yenisei river:1) radionuclide distribution in the Yenisei''s bottom sediment is nonuniform-"spotty"; 2) it is theoretically shown, that due to biological interactions and tro-phical radioniclide migration there is "spotive" type of space radionuclide distribution. The research is to make use of the novel methods of ecological biophysics:Monitoring:spectral analysis of surface waters (algal pigments), fluorescent techniques to evaluate productivity and condition of algae; rapid bioassays for water toxicity (bioluminescence, chemotaxis techniques). Kinetic experiments:microcosms on evaluating self-purification rates; special cultivators to evaluate the rates of growth of hydrobionts and radioactive engulfing, nutrition spectra; methods of finding growth limiting factors. Models:application of Bellman Principle to optimizing the river water use; theory and peculiarities of microbiological decomposition of pollutants in the river ecosystem. The composition of Prognostication Simulation Model is the next:1) hydrodynamical unit to calculate 2-dimensional space-time rate of stream on any depth; 2) hydrophysical unit to calculate:water temperature and level of solar radiation inside the water body; 3) ecosystem unit to calculate dynamic of concentration of phytoplankton, zooplankton, bacteria, major chemical matters and pollutants in water, content pollutants inside of hydrobionfs cells and dynamic of bentos; 4) radioe-cological unit to forecast the dynamic of radionuclides in the water body and bottom, their hydro-bont''s concentration; 5) database. Reservoirs and river models are provided by monitoring and kinetic experiments data. 相似文献
35.
Larry V. Benson Joseph P. Smoot Michaele Kashgarian Andrei Sarna-Wojcicki James W. Burdett 《Quaternary Research》1997,47(3):251-260
Uncalibrated radiocarbon data from core PLC92B taken from Wizards Cove in the Pyramid Lake subbasin indicate that the Trego Hot Springs and Wono tephra layers were deposited 23,200 ± 300 and 27,300 ± 30014C yr B.P. (uncorrected for reservoir effect). Sedimentological data from sites in the Pyramid Lake and Smoke Creek–Black Rock Desert subbasins indicate that the Trego Hot Springs tephra layer was deposited during a relatively dry period when Pyramid Lake was at or below its spill point (1177 m) to the Winnemucca Lake subbasin. The Wono tephra layer was deposited when lake depth was controlled by spill across Emerson Pass sill (1207 m) to the Smoke Creek–Black Rock Desert subbasin.18O data from core PLC92B also support the concept that the Trego Hot Springs tephra fell into a relatively shallow Pyramid Lake and that the Wono tephra fell into a deeper spilling lake. 相似文献
36.
Anastasiia Kurgaeva Sergey Sedov Sol Moreno-Roso Hermenegildo Barceinas Cruz Beatriz Ortega Guerrero Elizabeth Solleiro-Rebolledo Andrei Sinitsyn 《Geoarchaeology》2024,39(2):143-167
In geoarchaeological studies, there is an issue with distinguishing between natural and anthropogenic signals in pedological paleoarchives. With the pedostratigraphy of the Upper Paleolithic site of Kostenki 14, this issue is reflected by problems with the determination of features of pedogenic and pyrogenic processes. This issue was addressed by means of a thorough analysis of the magnetic properties of paleosols accompanied by micromorphological observations. Most of the humic samples were shown to be a result of pedogenesis, but two samples (a Paleolithic hearth sample and a sample from paleosol IIc) had features of intensely burnt material. The difference in the typical intensity of large-scale (natural or human-induced) and local-scale anthropogenic fire allowed for suggesting that the magnetic properties of the burnt sample were the result of an anthropogenically controlled fire event, that is, a hearth. This study shows that the magnetic properties of paleosols can be used to differentiate anthropogenic activity, in particular—burning, from pedogenic processes. This indicator is especially helpful in finding disturbed combustion features when the hearth structure is lost. This methodology used to demonstrate the local human-induced pyrogenic effect at the Upper Paleolithic site can contribute to the discussion of the niche construction effect of human activities in the Pleistocene. 相似文献
37.
Numerical simulations of a highway bridge structure employing passive negative stiffness device for seismic protection 下载免费PDF全文
Navid Attary Michael Symans Satish Nagarajaiah Andrei M. Reinhorn Michael C. Constantinou Apostolos A. Sarlis Dharma T. R. Pasala Douglas Taylor 《地震工程与结构动力学》2015,44(6):973-995
A new passive seismic response control device has been developed, fabricated, and tested by the authors and shown to be capable of producing negative stiffness via a purely mechanical mechanism, thus representing a new generation of seismic protection devices. Although the concept of negative stiffness may appear to be a reversal on the desired relationship between the force and displacement in structures (the desired relationship being that the product of restoring force and displacement is nonnegative), when implemented in parallel with a structure having positive stiffness, the combined system appears to have substantially reduced stiffness while remaining stable. Thus, there is an ‘apparent weakening and softening’ of the structure that results in reduced forces and increased displacements (where the weakening and softening is of a non‐damaging nature in that it occurs in a seismic protection device rather than within the structural framing system). Any excessive displacement response can then be limited by incorporating a damping device in parallel with the negative stiffness device. The combination of negative stiffness and passive damping provides a large degree of control over the expected performance of the structure. In this paper, a numerical study is presented on the performance of a seismically isolated highway bridge model that is subjected to various strong earthquake ground motions. The Negative Stiffness Devices (NSDs) are described along with their hysteretic behavior as obtained from a series of cyclic tests wherein the tests were conducted using a modified design of the NSDs (modified for testing within the bridge model). Using the results from the cyclic tests, numerical simulations of the seismic response of the isolated bridge model were conducted for various configurations (with/without negative stiffness devices and/or viscous dampers). The results demonstrate that the addition of negative stiffness devices reduces the base shear substantially, while the deck displacement is limited to acceptable values. This assessment was conducted as part of a NEES (Network for Earthquake Engineering Simulation) project which included shaking table tests of a quarter‐scale highway bridge model. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
38.
Nadezhda Priyatkina William J. Collins Andrei Khudoley Dmitry Zastrozhnov Victoria Ershova Kevin Chamberlain 《International Geology Review》2017,59(13):1632-1656
Identifying the cratonic affinity of Neoproterozoic crust that surrounds the northern margin of the Siberian Craton (SC) is critical for determining its tectonic evolution and placing the Craton in Neoproterozoic supercontinental reconstructions. Integration of new U–Pb–Hf detrital zircon data with regional geological constraints indicates that distinct Neoproterozoic arc-related magmatic belts can be identified within the Taimyr orogen. Sedimentary rocks derived from 970 to 800 Ma arc-related suites reveal abundant Archean and Paleoproterozoic detritus, characteristic of the SC. The 720–600 Ma arc-related zircon population from the younger Cambrian sedimentary rocks is also complemented by an exotic juvenile Mesoproterozoic zircon population and erosional products of older arc-related suites. Nonetheless, numerous evidences imply that both arcs broadly reworked Siberian basement components. We suggest that the early Neoproterozoic (ca. 970–800 Ma) arc system of the Taimyr orogen evolved on the active margin of the SC and probably extended along the periphery of Rodinia into Valhalla orogen of NE Laurentia. We also suggest the late Neoproterozoic (750–550 Ma) arc system could have been part of the Timanian orogen, which linked Siberia and Baltica at the Precambrian/Phanerozoic transition. 相似文献
39.
The marine controlled source electromagnetic response of a steel borehole casing: applications for the NEPTUNE Canada gas hydrate observatory 总被引:1,自引:0,他引:1
Gas hydrates are a potential energy resource, a possible factor in climate change and an exploration geohazard. The University of Toronto has deployed a permanent seafloor time‐domain controlled source electromagnetic (CSEM) system offshore Vancouver Island, within the framework of the NEPTUNE Canada underwater cabled observatory. Hydrates are known to be present in the area and due to their electrically resistive nature can be monitored by 5 permanent electric field receivers. However, two cased boreholes may be drilled near the CSEM site in the near future. To understand any potential distortions of the electric fields due to the metal, we model the marine electromagnetic response of a conductive steel borehole casing. First, we consider the commonly used canonical model consisting of a 100 Ωm, 100 m thick resistive hydrocarbon layer embedded at a depth of 1000 m in a 1 Ωm conductive host medium, with the addition of a typical steel production casing extending from the seafloor to the resistive zone. Results show that in both the frequency and time domains the distortion produced by the casing occurs at smaller transmitter‐receiver offsets than the offsets required to detect the resistive layer. Second, we consider the experimentally determined model of the offshore Vancouver Island hydrate zone, consisting of a 5.5 Ωm, 36 m thick hydrate layer overlying a 0.7 Ωm sedimentary half‐space, with the addition of two borehole casings extending 300 m into the seafloor. In this case, results show that the distortion produced by casings located within a 100 m safety zone of the CSEM system will be measured at 4 of the 5 receivers. We conclude that the boreholes must be positioned at least 200 m away from the CSEM array so as to minimize the effects of the casings. 相似文献
40.
Vertical and Horizontal Transport of Energy and Matter by Coherent Motions in a Tall Spruce Canopy 总被引:2,自引:2,他引:0
In the framework of the EGER (ExchanGE processes in mountainous Regions) project, the contribution of coherent structures
to vertical and horizontal transports in a tall spruce canopy is investigated. The combination of measurements done in both
the vertical and horizontal directions allows us to investigate coherent structures, their temporal scales, their role in
flux transport, vertical coupling between the sub-canopy, canopy and air above the canopy, and horizontal coupling in the
sub-canopy layer. The temporal scales of coherent structures detected with the horizontally distributed systems in the sub-canopy
layer are larger than the temporal scales of coherent structures detected with the vertically distributed systems. The flux
contribution of coherent structures to the momentum and sensible heat transport is found to be dominant in the canopy layer.
Carbon dioxide and latent heat transport by coherent structures increase with height and reach a maximum at the canopy height.
The flux contribution of the ejection decreases with increasing height and becomes dominant above the canopy level. The flux
fraction transported during the sweep increases with height and becomes the dominant exchange process at the upper canopy
level. The determined exchange regimes indicate consistent decoupling between the sub-canopy, canopy and air above the canopy
during evening, nighttime and morning hours, whereas the coupled states and coupled by sweep states between layers are observed
mostly during the daytime. Furthermore, the horizontal transport of sensible heat by coherent structures is investigated,
and the heterogeneity of the contribution of coherent events to the flux transport is demonstrated. A scheme to determine
the horizontal coupling by coherent structures in the sub-canopy layer is proposed, and it is shown that the sub-canopy layer
is horizontally coupled mainly in the wind direction. The vertical coupling in most cases is observed together with streamwise
horizontal coupling, whereas the cross-stream direction is decoupled. 相似文献