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601.
David P. Rowell 《Climate Dynamics》2005,25(7-8):837-849
A scenario of European climate change for the late twenty-first century is described, using a high-resolution state-of-the-art
model. A time-slice approach is used, whereby the atmospheric general circulation model, HadAM3P, was integrated for two periods,
1960–1990 and 2070–2100, using the SRES A2 scenario. For the first time an ensemble of such experiments was produced, along
with appropriate statistical tests for assessing significance. The focus is on changes to the statistics of seasonal means,
and includes analysis of both multi-year means and interannual variance. All four seasons are assessed, and anomalies are
mapped for surface air temperature, precipitation and snow mass. Mechanisms are proposed where these are dominated by straightforward
local processes. In winter, the largest warming occurs over eastern Europe, up to 7°C, mean snow mass is reduced by at least
80% except over Scandinavia, and precipitation increases over all but the southernmost parts of Europe. In summer, temperatures
rise by 6–9°C south of about 50°N, and mean rainfall is substantially reduced over the same area. In spring and autumn, anomalies
tend to be weaker, but often display patterns similar to the preceding season, reflecting the inertia of the land surface
component of the climate system. Changes in interannual variance are substantial in the solsticial seasons for many regions
(note that for precipitation, variance estimates are scaled by the square of the mean). In winter, interannual variability
of near-surface air temperature is considerably reduced over much of Europe, and the relative variability of precipitation
is reduced north of about 50°N. In summer, the (relative) interannual variance of both variables increases over much of the
continent. 相似文献
602.
W. David Rust Donald R. MacGorman Eric C. Bruning Stephanie A. Weiss Paul R. Krehbiel Ronald J. Thomas William Rison Timothy Hamlin Jeremiah Harlin 《Atmospheric Research》2005,76(1-4):247
Balloon-borne electric field soundings and lightning mapping data have been analyzed for three of the storms that occurred in the Severe Thunderstorm Electrification and Precipitation Study field program in 2000 to determine if the storms had inverted-polarity electrical structures. The polarities of all or some of the vertically stacked charge regions in such storms are opposite to the polarities observed at comparable heights in normal storms. Analyses compared the charge structures inferred from electric field soundings in the storms with charges inferred from three-dimensional lightning mapping data. Charge structures were inferred from electric field profiles by combining the one-dimensional approximation of Gauss's law with additional information from three-dimensional patterns in the electric field vectors. The three different ways of inferring the charge structure in the storms were found to complement each other and to be consistent overall. Charge deposition by lightning possibly occurred and increased the charge complexity of one of the storms.Many of the cloud flashes in each case were inverted-polarity flashes. Two storms produced ground flash activity comprised predominantly of positive ground flashes. One storm, which was an isolated thunderstorm, produced inverted-polarity cloud flashes, but no flashes to ground. The positive and negative thunderstorm charge regions were found at altitudes where, respectively, negative and positive charge would be found in normal-polarity storms. Thus, we conclude that these storms had anomalous and inverted-polarity electrical structures. Collectively, these three cases (along with the limited cases in the refereed literature) provide additional evidence that thunderstorms can have inverted-polarity electrical structures. 相似文献
603.
Seismic anisotropy beneath Dronning Maud Land, Antarctica, revealed by shear wave splitting 总被引:1,自引:0,他引:1
Bettina Bayer Christian Müller David W. Eaton Wilfried Jokat 《Geophysical Journal International》2007,171(1):339-351
Shear wave splitting analyses have been carried out using teleseismic data from broad-band seismograph stations deployed at temporary and permanent locations in Dronning Maud Land (DML), Antarctica. In most cases, the observed anisotropy can be related to major tectonic events that formed the present-day Antarctic continent. We rule out an anisotropic contribution from recent asthenospheric flow. At the Russian base Novolazarevskaya near the coast in central DML, waveform inversion suggests a two-layer model where the fast direction of the upper layer is oriented parallel to Archean fabrics in the lithosphere, whereas the anisotropy of the lower layer is interpreted to have been created during the Jurassic Gondwana break-up. Recordings at the South African base Sanae IV, however, show enigmatic results. For narrow backazimuthal segments, splitting parameters show strong variations together with a multitude of isotropic measurements, indicative of complex scattering that cannot be explained by simple one- or two-layer anisotropic models. In the interior of the continent, the data are consistent with single-layer anisotropy, but show significant spatial variations in splitting parameters. A set of temporary stations across the Heimefront shear zone in western DML yield splitting directions that we interpret as frozen anisotropy from Proterozoic assembly of the craton. An abrupt change in fast axis direction appears to mark a suture between the Grunehogna craton, a fragment of the Kalahari–Kaapvaal craton in southern Africa and the Mesoproterozoic Maudheim Province. 相似文献
604.
David Al-Attar 《Geophysical Journal International》2007,171(2):755-760
A formal solution to the elastodynamic equation in an anelastic earth model is presented. The derivation also incorporates the effects of aspherical structure, rotation, self-gravitation, and pre-stress. It is found that the solution can be expressed as a sum of the normal modes of the earth model along with additional terms accounting for anelastic relaxation processes. However, the derivation does not assume that such an eigenfunction expansion is possible, and so avoids difficulties previously encountered due to the non self-adjointness of the problem. 相似文献
605.
606.
Nature-triggered hazards and disasters have traditionally been treated only from the lens of geophysical and biophysical processes,
implying that the root cause of large-scale death and destruction lies in the natural domain rather than in a coupled human–environment
system. Conceptually, the physical domain has been seen as discrete and separate from human entities, and solutions were sought
in the technological intervention and control of the physical environment—solutions that often ended up being less effective
than hoped for and sometimes even counter productive. At all levels, institutions have directed and redirected most of their
financial and logistical resources into the search for scientific and engineering solutions without allocating due attention
and resources towards the assessment of effects and effectiveness of the applications of such technological outcomes. However,
over the last two decades, forceful criticisms of the ‘dominant’ technocratic approach to hazards analysis have appeared in
the literature and consequently there has not only been a shift in thinking of causation of disaster loss in terms of human
vulnerability, but also newer questions have arisen regarding distinguishing between the ‘physical exposure’ of people to
threats and societal vulnerability, and linking them with propensity to hazards loss.
Though the vulnerability/resilience paradigm has largely replaced the hazards paradigm within the social sciences and much
of the professional emergency and disaster management communities, this shift of thinking has not progressed to much of the
physical science community, decision-makers and the public, who have not yet accepted the idea that understanding and using
human and societal dimensions is equally or more important than trying to deal and control nature through the use of technology.
This special issue is intended to further the idea that the aspects of community and peoples’ power to mitigate, to improve
coping mechanisms, to respond effectively, and recover with vigor against the environmental extremes are of paramount conceptual
and policy importance. 相似文献
607.
There is an exceptionally rich aquatic fauna in the epikarst, the skin of karst. High species richness in the epikarst, coupled
with its special vulnerability as the first point of entry of nearly all toxic spills, makes its protection especially important.
The epikarst fauna may also be an useful tool in tracing the potential route of pollutants. Copepods in epikarst have extremely
local distributions, and their body size is such that they are largely at the mercy of directional flows. In a series of caves
in southwest Slovenia and West Virginia, a significant fraction of the copepod species occur in less than 100 m of linear
extent. This suggests a pattern of highly restricted lateral flow under normal conditions and the distribution of copepods
could potentially be used to trace water movement. Under high flow conditions as would often be the case with toxic spill,
mounding of water may increase the lateral radius of flow. Nevertheless, copepods may be useful tracers. 相似文献
608.
609.
The primary factors that control the concentration of total reduced (inorganic) sulfide in coastal sediments are believed
to be the availability of reactive iron, dissolved sulfate and metabolizable organic carbon. We selected nine sites in shallow
(<3 m), close to sub-tropical, estuaries and bays along the central Texas coast that represented a range in sediment grain
size (a proxy for reactive iron), salinity (a proxy for dissolved sulfate), and total organic carbon (a proxy for metabolizable
organic carbon). Based on these parameters a prediction was made of which factor was likely to control total reduced sulfide
at each site and what the relative total reduced sulfide concentration was likely to be. To test the prediction, the sediments
were analyzed for total reduced sulfide, acid volatile sulfide, and citrate dithionate-extractable, HCl-extractable and total
Fe in the solid phase. Using solid-state gold–mercury amalgam microelectrodes and voltammetry, we determined pore water depth
profiles of Fe(II) and ΣH2S and presence or absence of FeS(aq). At five of the nine sites the calculated degree of sufildization of citrate dithionite-reactive-iron was close to or greater
than 1 indicating that rapidly reactive iron was probably the limiting factor for iron sulfide mineral formation. At one site
(salinity = 0.9) dissolved Fe(II) was high, ΣH2S was undetectable and the total reduced sulfide concentration was low indicating sulfate limitation. At the last three sites
a low degree of sulfidization and modest total reduced (inorganic) sulfide concentrations appeared to be the result of a limited
supply of metabolizable organic carbon. Fe(II)–S(-II) clusters (FeS(aq)) were undetectable in 10 out of 12 bay sediment profiles where ΣH2S was close to or below detection limits, but was observed in all other porewater profiles. Acid volatile sulfide, but not
total reduced sulfide, was well correlated with total organic carbon and ranged from being undetectable in some cores to representing
a major portion of total reduced sulfide in other cores. Although predicted controls on total reduced sulfide were good for
very low salinity water or sandy sediments, they were only right about half the time for the other sediments. The likely reasons
for the wrong predictions are the poor correlation of total organic carbon with grain size and differing fractions of metabolizable
organic carbon in different sedimentary environments. Differences in sediment accumulation rates may also play a role, but
these are difficult to determine in this region where hurricanes often resuspend and move sediments. This study demonstrates
the need to examine more complex and often difficult to determine parameters in anoxic “normal marine” sediments if we are
to understand what controls the concentration and distribution of sulfides. 相似文献
610.