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91.
Hugues Lantuit Pier Paul Overduin Nicole Couture Sebastian Wetterich Felix Aré David Atkinson Jerry Brown Georgy Cherkashov Dmitry Drozdov Donald Lawrence Forbes Allison Graves-Gaylord Mikhail Grigoriev Hans-Wolfgang Hubberten James Jordan Torre Jorgenson Rune Strand ?deg?rd Stanislav Ogorodov Wayne H. Pollard Volker Rachold Sergey Sedenko Steve Solomon Frits Steenhuisen Irina Streletskaya Alexander Vasiliev 《Estuaries and Coasts》2012,35(2):383-400
Arctic permafrost coasts are sensitive to changing climate. The lengthening open water season and the increasing open water area are likely to induce greater erosion and threaten community and industry infrastructure as well as dramatically change nutrient pathways in the near-shore zone. The shallow, mediterranean Arctic Ocean is likely to be strongly affected by changes in currently poorly observed arctic coastal dynamics. We present a geomorphological classification scheme for the arctic coast, with 101,447?km of coastline in 1,315 segments. The average rate of erosion for the arctic coast is 0.5?m? year?1 with high local and regional variability. Highest rates are observed in the Laptev, East Siberian, and Beaufort Seas. Strong spatial variability in associated database bluff height, ground carbon and ice content, and coastline movement highlights the need to estimate the relative importance of shifting coastal fluxes to the Arctic Ocean at multiple spatial scales. 相似文献
92.
Robert G. Strom Maria E. Banks Clark R. Chapman Caleb I. Fassett Jeffrey A. Forde James W. Head III William J. Merline Louise M. Prockter Sean C. Solomon 《Planetary and Space Science》2011,59(15):1960-1967
The primary crater population on Mercury has been modified by volcanism and secondary craters. Two phases of volcanism are recognized. One volcanic episode that produced widespread intercrater plains occurred during the period of the Late Heavy Bombardment and markedly altered the surface in many areas. The second episode is typified by the smooth plains interior and exterior to the Caloris basin, both of which have a different crater size-frequency distribution than the intercrater plains, consistent with a cratering record dominated by a younger population of impactors. These two phases may have overlapped as parts of a continuous period of volcanism during which the volcanic flux tended to decrease with time. The youngest age of smooth plains volcanism cannot yet be determined, but at least small expanses of plains are substantially younger than the plains associated with the Caloris basin. The spatial and temporal variations of volcanic resurfacing events can be used to reconstruct Mercury's geologic history from images and compositional and topographic data to be acquired during the orbital phase of the MESSENGER mission. 相似文献
93.
Jürgen Oberst Stephan Elgner F. Scott Turner Mark E. Perry Robert W. Gaskell Maria T. Zuber Mark S. Robinson Sean C. Solomon 《Planetary and Space Science》2011,59(15):1918-1924
Analysis of images obtained by the MESSENGER spacecraft during its three flybys of Mercury yields a new estimate for the planet's mean radius of 2439.25±0.69 km, in agreement with results from Mariner 10 and Earth-based observations, as well as with MESSENGER altimeter and occultation data. The mean equatorial radius and polar radius are identical to within error, suggesting that rotational oblateness is negligible when compared with other sources of topography. This result is consistent with the small gravitational oblateness of the planet. Minor differences in radius obtained at different locations reflect regional variations in topography. Residual topography along three limb profiles has a dynamic range of 7.4 km and a root-mean-square roughness of 0.8 km over hemispherical scales. Following MESSENGER's entry into orbit about Mercury in March 2011, we expect considerable additional improvements to our knowledge of Mercury's size and shape. 相似文献
94.
Laura Kerber James W. Head David T. Blewett Sean C. Solomon Lionel Wilson Scott L. Murchie Mark S. Robinson Brett W. Denevi Deborah L. Domingue 《Planetary and Space Science》2011,59(15):1895-1909
We present a global survey of candidate pyroclastic deposits on Mercury, derived from images obtained during MESSENGER flybys 1–3 that provided near-global coverage at resolutions between 5 and 0.5 km/pixel. Thirty-five deposits were identified and characterized and are located principally on the floors of craters, along rims of craters, and along the edge of the Caloris basin. Deposits are commonly centered on rimless, often irregularly shaped pits, mostly between 5 and 45 km in diameter. The deposits identified are generally similar in morphology and absolute reflectance to lunar pyroclastic deposits. Spectrally the deposits appear brighter and redder than background Mercury terrain. On the basis of the available coverage, the candidate pyroclastic deposits appear to be essentially globally distributed. The diameters of the deposits, when mapped to lunar gravity conditions, are larger than their lunar counterparts, implying that more abundant volatiles were present during the typical eruptive process than on the Moon. These observations indicate that if these deposits resulted from hawaiian-style eruptions, the volatile contents required would be between ~1600 and 16,000 ppm CO or an equivalent value of H2O, CO2, SO2, or H2S (for a more oxidizing interior), or N2, S2, CS2, S2Cl, Cl, Cl2, or COS (for a more reducing interior). These abundances are much greater than those predicted by existing models for Mercury's formation. An apparent lack of small deposits, compared with the Moon, may be due to resolution effects, a topic that can be further assessed during the orbital phase of the MESSENGER mission. These results provide a framework within which orbital observations by MESSENGER and the future BepiColombo mission can be analyzed. 相似文献
95.
Daniel N. Baker Dusan Odstrcil Brian J. Anderson C. Nick Arge Mehdi Benna George Gloeckler Haje Korth Leslie R. Mayer Jim M. Raines David Schriver James A. Slavin Sean C. Solomon Pavel M. Trávní?ek Thomas H. Zurbuchen 《Planetary and Space Science》2011,59(15):2066-2074
The second and third flybys of Mercury by the MESSENGER spacecraft occurred, respectively, on 6 October 2008 and on 29 September 2009. In order to provide contextual information about the solar wind properties and the interplanetary magnetic field (IMF) near the planet at those times, we have used an empirical modeling technique combined with a numerical physics-based solar wind model. The Wang–Sheeley–Arge (WSA) method uses solar photospheric magnetic field observations (from Earth-based instruments) in order to estimate the inner heliospheric radial flow speed and radial magnetic field out to 21.5 solar radii from the Sun. This information is then used as input to the global numerical magnetohydrodynamic model, ENLIL, which calculates solar wind velocity, density, temperature, and magnetic field strength and polarity throughout the inner heliosphere. WSA-ENLIL calculations are presented for the several-week period encompassing the second and third flybys. This information, in conjunction with available MESSENGER data, aid in understanding the Mercury flyby observations and provide a basis for global magnetospheric modeling. We find that during both flybys, the solar wind conditions were very quiescent and would have provided only modest dynamic driving forces for Mercury's magnetospheric system. 相似文献
96.
Acoustic signals received by platform mounted sonar arrays can be spatially processed to enhance the detection of targets in the presence of both ambient and platform generated (self) noise. Ambient noise in the ocean, such as that due to distant shipping or biological choruses, are known to be spatially correlated. The platform generated noise will be of near-field origin and may not be received by all elements in the array. In this paper we investigate the performance of the minimum variance distortionless response (MVDR) beamformer and the recently introduced Fourier integral method (FIM) and compare their performances with the conventional beamformer. Real passive sonar data, obtained from a platform mounted sparse linear array of hydrophones, is used to study the performance of the beamformers in a typical sonar environment. It is shown that in the absence of self noise, when the array is accurately calibrated the MVDR beamformer will perform very well, but when sensor gain or phase errors are present the performance of the MVDR beamformer is degraded. Further, the MVDR beamformer is unable to reject the self noise which is not "seen" by the entire array. FIM however seems to perform well and a modified version of FIM, which we call weighted FIM (WFIM), is shown to perform better and is at worst comparable to a well calibrated MVDR beamformer 相似文献
97.
Q. Wu D.A. Ortland S.C. Solomon W.R. Skinner R.J. Niciejewski 《Journal of Atmospheric and Solar》2011,73(17-18):2482-2502
Based on TIDI mesospheric wind observations, we analyzed the semidiurnal tide westward zonal wavenumber 1 and 2 (SW1 and SW2) component seasonal, inter-annual variations, and possible sudden stratospheric warming (SSW) related changes. Major findings are as follows: (1) The SW1 has a peak near the South Pole during the December solstice and near the North Pole during the March equinox. (2) The SW2 peaks at 60S and 60N mostly during winter solstices. The SW2 also peaks during late summer and early fall in the northern hemisphere. (3) The QBO effect on the semidiurnal tide is much weaker than that on the diurnal tide. The March equinox northern SW1 zonal amplitude appears to be stronger during the westward phase of the QBO, which is opposite of migrating diurnal tide QBO response. (4) Possible SSW event related changes in the semidiurnal tide are significant but not always consistent. Enhancements in the mid-latitude SW2 component during SSWs are observed, which may be related to the increase of total ozone at mid and high latitudes during SSW events. TIDI observations also show a decrease in the SW2 in the opposite hemisphere during a southern SSW event in 2002. Small increases in the high latitude SW1 in both hemispheres during the 2002 southern SSW event were recorded. 相似文献
98.
Except for the fringing reef, the limestones of Christmas Island in the Indian Ocean are of Late Eocene (Tertiary “b") and Early Miocene (Tertiary “e” to “f") age. The Upper Eocene limestone is an algal limestone containing Discocyclina, Nummulites, and Heterostegina. The Lower Miocene limestone is an algal limestone containing in its lower part species of Lepidocyclina (Eulepidina) followed by Miogypsinoides dehaarti. Miogypsinoides dehaarti extends into the zone of Flosculinella bontangensis. No rocks younger than Burdigalian were identified other than on the fringing reef which contains an assemblage of Pliocene‐Pleistocene Foraminifera. 相似文献
99.
Michael H. Ramsey Grace Solomon‐Wisdom Ariadne Argyraki 《Geostandards and Geoanalytical Research》2013,37(4):379-391
A general method for the evaluation of in situ heterogeneity of geochemical materials is described and the significance of the results discussed, by using three case studies and earlier data sets. The heterogeneity of Pb in soil (expressed as RSD due to sampling, RSDsamp) varies from < 5 to > 100% between different sites, in a way that relates to the mode of deposition of the element. The heterogeneity of an element also varies systematically as a function of the distance scale at some sites. This variation can be modelled using linear regression, accounting for over 90% of the experimental variance, at seven scales over three orders of magnitude. Variation in heterogeneity between elements at the same site, seems to be somewhat diagnostic of the origin of the element, lithogenic being less than anthropogenic, although the later is also being modified by the mode of deposition. Where the heterogeneity is large (RSD > 30%), it is proposed that it can be expressed more accurately as a heterogeneity factor (10GSDsamp), to reflect its frequency distribution, which is positively skewed towards higher concentration values. 相似文献
100.
Are violent conflict and socio-political stability associated with changes in climatological variables? We examine 50 rigorous quantitative studies on this question and find consistent support for a causal association between climatological changes and various conflict outcomes, at spatial scales ranging from individual buildings to the entire globe and at temporal scales ranging from an anomalous hour to an anomalous millennium. Multiple mechanisms that could explain this association have been proposed and are sometimes supported by findings, but the literature is currently unable to decisively exclude any proposed pathway. Several mechanisms likely contribute to the outcomes that we observe. 相似文献