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排序方式: 共有116条查询结果,搜索用时 15 毫秒
61.
The Changing Incidence of Extremes in Worldwide and Central England Temperatures to the End of the Twentieth Century 总被引:2,自引:0,他引:2
Annual and seasonal gridded ocean surface temperature anomalies show an increase in warm extremes and a decrease in cold extremes since the late 19th century attributable entirely to the overall warming trend. Over land, however, a reduction in the total incidence of extremes may reflect improved instrumental exposures. Our estimates of extremes are made by deriving percentiles from fits of anomalies on 5° latitude ×5° longitude resolution to modified 2-parameter gamma distributions. A non-parametric method is used to check the validity of the results. Fields of percentiles created using this technique can be used to map the distribution of unusual temperature anomalies across the globe on any time scale from a month to about a decade, from 1870 onwards. We apply a similar technique to assess changes in the incidence of extreme daily Central England temperature anomalies. The incidence of these extremes, relative to individual monthly average temperatures, has declined. 相似文献
62.
The metal content of the eucrite parent body: constraints from the partitioning behavior of tungsten
The solid metal/silicate melt partition coefficient for W has been determined experimentally to have a value of 25 ± 5 at 1190°C and an oxygen fugacity of 10?13.4, the temperature and oxygen fugacity conditions at which eucritic basalts formed. Given this partition coefficient, scenarios for the metal content and evolution of the eucrite parent body (EPB) are constructed to explain the reduction by a factor of 30, relative to the chondrites, of the ratio in the eucrites.A possible model for the early geologic history of the EPB begins with accretion of a parent body, chondritic in composition with respect to nonvolatile siderophile and lithophile elements. The solid metal content was between 2% and 10%, which is within the range observed in the ordinary chondrites. Subsequent heating of the EPB caused the metal phase to separate and become isolated from the silicate phases before the degree of partial melting of the silicates reached 4% to 5%. Equilibrium partitioning of most of the W into the solid metal phase at low degrees of partial melting reduced the ratio in the remaining silicates. Continued partial melting of the silicates generated primary eucritic magmas which recorded the reduced ratio. 相似文献
63.
Glyn Williams-Jones Keith A. Horton Tamar Elias Harold Garbeil Peter J. Mouginis-Mark A. Jeff Sutton Andrew J. L. Harris 《Bulletin of Volcanology》2006,68(4):328-332
A fundamental problem with all ground-based remotely sensed measurements of volcanic gas flux is the difficulty in accurately
measuring the velocity of the gas plume. Since a representative wind speed and direction are used as proxies for the actual
plume velocity, there can be considerable uncertainty in reported gas flux values. Here we present a method that uses at least
two time-synchronized simultaneously recording UV spectrometers (FLYSPECs) placed a known distance apart. By analyzing the
time varying structure of SO2 concentration signals at each instrument, the plume velocity can accurately be determined. Experiments were conducted on
Kīlauea (USA) and Masaya (Nicaragua) volcanoes in March and August 2003 at plume velocities between 1 and 10 m s−1. Concurrent ground-based anemometer measurements differed from FLYSPEC-measured plume speeds by up to 320%. This multi-spectrometer
method allows for the accurate remote measurement of plume velocity and can therefore greatly improve the precision of volcanic
or industrial gas flux measurements.
Editorial responsibility: A. Woods 相似文献
64.
J. H. Carver B. H. Horton R. S. O'Brien G. G. O'Connor 《Earth, Moon, and Planets》1974,9(3-4):295-303
The ultraviolet flux from the entire lunar disk has been measured in a series of rocket flights from Woomera at several wavelength bands in the range 2400-2900 Å and also at the wavelength of the hydrogen Lα line (1216 Å). Comparison of these measurements with other observations shows that between the visible and middle ultraviolet part of the spectrum, the lunar albedo decreases sharply towards shorter wavelengths falling to (0.7 ± 0.1) percent at 2400 Å which is a factor of ten less than the visible albedo. The measured albedo at 1216 Å is (0.3 ± 0.1) percent indicating that the decline in reflectivity with decreasing wavelength is less rapid at far ultraviolet wavelengths than is the decline between visible and middle ultraviolet. 相似文献
65.
This research analyses the diatom asssemblages recorded from six UK coastal sites and relates these diatom assemblages to tidal levels. The relationship between diatom assemblages and tidal levels is examined statistically in order to develop a diatom‐based tidal‐level transfer function. The results suggest that there is highly significant correlation between the diatom assemblages and water levels from mean high water of neap tides to highest astronomical tide (p = 0.01, 99 random permutations). A weighted average (WA) transfer function is thus established, and the predictive ability of this transfer function is highly satisfactory. Finally, this transfer function is applied successfully to estimate palaeotidal‐levels from fossil diatom data recorded in late Holocene coastal sequences. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
66.
Generous statistical tests 总被引:1,自引:1,他引:0
T. V. Hromadka II R. J. Whitley S. B. Horton M. J. Smith J. M. Lindquist 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(1):9-12
A common statistical problem is deciding which of two possible sources, A and B, of a contaminant is most likely the actual
source. The situation considered here, based on an actual problem of polychlorinated biphenyl contamination discussed below,
is one in which the data strongly supports the hypothesis that source A is responsible. The problem approach here is twofold:
One, accurately estimating this extreme probability. Two, since the statistics involved will be used in a legal setting, estimating
the extreme probability in such a way as to be as generous as is possible toward the defendant’s claim that the other site
B could be responsible; thereby leaving little room for argument when this assertion is shown to be highly unlikely. The statistical
testing for this problem is modeled by random variables {X
i
} and the corresponding sample mean the problem considered is providing a bound ɛ for which for a given number a
0. Under the hypothesis that the random variables {X
i
} satisfy E(X
i
) ≤ μ, for some 0 < μ < 1, statistical tests are given, described as “generous”, because ɛ is maximized. The intent is to
be able to reject the hypothesis that a
0 is a value of the sample mean while eliminating any possible objections to the model distributions chosen for the {X
i
} by choosing those distributions which maximize the value of ɛ for the test used. 相似文献
67.
68.
Horton E. Newsom Nina L. Lanza Sandra M. Wiseman Giuseppe A. Marzo Chris H. Okubo Victoria E. Hamilton 《Icarus》2010,205(1):64-72
Morphological features on the western floor of Miyamoto crater in southwestern Meridiani Planum, Mars, are suggestive of past fluvial activity. Imagery from the High Resolution Imaging Science Experiment (HiRISE) gives a detailed view of raised curvilinear features that appear to represent inverted paleochannel deposits. The inverted terrain appears to be capped with a resistant, dark-toned deposit that is partially covered by unconsolidated surficial materials. Subsequent to deposition of the capping layer, erosion of the surrounding material has left the capping materials perched on pedestals of uneroded basal unit material. Neither the capping material nor the surrounding terrains show any unambiguous morphological evidence of volcanism or glaciation. The capping deposit may include unconsolidated or cemented stream deposits analogous to terrestrial inverted channels in the Cedar Mountain Formation near Green River, Utah. In addition to this morphological evidence for fluvial activity, phyllosilicates have been identified in the basal material on the floor of Miyamoto crater by orbital spectroscopy, providing mineralogical evidence of past aqueous activity. Based on both the morphological and mineralogical evidence, Miyamoto crater represents an excellent site for in situ examination and sampling of a potentially habitable environment. 相似文献
69.
The concentrations of 45 elements in ambient (not obviously disturbed) surface soils were determined for 57 sites distributed throughout the city of Chicago, Illinois in the upper Midwestern United States. These concentrations were compared to soils from 105 sites from a largely agricultural region within a 500-km radius surrounding the city and to soils collected from 90 sites across the state of Illinois. Although the bulk composition of the Chicago urban soils reflects largely natural sources, the soils are significantly enriched in many trace elements, apparently from anthropogenic sources. The median concentration of Pb in Chicago soils is 198 mg/kg, a 13-fold enrichment compared to regional concentrations. Zinc (median 235 mg/kg), Cu (59 mg/kg), and Ni (31 mg/kg) are also enriched from 2- to 4-fold in Chicago soils and all four elements show strong mutual correlations. These elevated concentrations are most likely related to vehicular and roadway sources and represent uneven distribution across the city as airborne material. Other airborne particulate material from a combination of fossil fuel combustion, waste incineration, and steel production may contribute to apparent elevated concentrations in Chicago soil of Fe (median 2.9%), Mo (5 mg/kg), V (82 mg/kg) and S (0.09%). Chicago soils are enriched from about 1.6- to 3-fold in these elements. Enrichments in P and Se may be caused by direct addition of phosphate fertilizer to parklands, lawns and gardens. The density of the sampling (1 site per 10 km2) is inadequate to define the distribution of the observed enrichments within the city or to predict soil compositions for most of the areas between sample sites, but does provide a statistically significant signature of the history of urban and industrial activity within the city in contrast to the surrounding agricultural lands. 相似文献
70.
Andrew C. Kemp Benjamin P. Horton Daria Nikitina Christopher H. Vane Marina Potapova Elizabeth Weber‐Bruya Stephen J. Culver Tatyana Repkina David F. Hill 《Boreas: An International Journal of Quaternary Research》2017,46(3):562-584
In support of efforts to reconstruct relative sea level (RSL), we investigated the utility of foraminifera, diatoms and bulk‐sediment geochemistry (δ13C, C:N and parameters measured by Rock‐Eval pyrolysis) as sea‐level indicators in Eurasian sub‐Arctic salt marshes. At three salt marshes (<15 km apart) in Dvina Bay (White Sea, Russia), we collected surface sediment samples along transects from subtidal to Taiga forest environments. Foraminifera at all sites formed bipartite assemblages, where elevations below mean high higher water (MHHW) were dominated by Miliammina spp. and elevations between MHHW and the highest occurrence of foraminifera were dominated by Jadammina macrescens and Balticammina pseudomacrescens. Five high‐diversity groups of diatoms were identified and they displayed pronounced variability amongst the study sites. Bulk‐sediment geochemistry recognized two groups (clastic‐dominated environments below MHHW and organic‐rich environments above MHHW). As one group included subtidal elevations and the other included supratidal elevations, we conclude that the measured geochemical parameters are not stand‐alone sea‐level indicators. Core JT2012 captured a regressive sediment succession of clastic, tidal‐flat sediment overlain by salt‐marsh organic silt and freshwater peat. The salt‐marsh sediment accumulated at 2804±52 years before present and preserved foraminifera (Jadammina macrescens and Balticammina pseudomacrescens) with good analogy to modern assemblages indicating that RSL was +2.60±0.47 m at this time. Diatoms confirm that marine influence decreased through time, but the lack of analogy between modern and core assemblages limited their utility as sea‐level indicators. Geochemical parameters also indicate a reduction in marine influence through time. We conclude that RSL reconstructions derived from salt‐marsh sediment preserved beneath Eurasian sub‐Arctic peatlands can provide valuable insight into the spatio‐temporal evolution of the Fennoscandian and Eurasian ice sheets. 相似文献