Vertical structure of the field of current velocities in the northwest part of the Black Sea based on the <Emphasis Type="Italic">LADCP</Emphasis> data for May 2004     

E. M. Lemeshko  A. N. Morozov  S. V. Stanichnyi  L. D. Mee  G. I. Shapiro 《Physical Oceanography》2008,18(6):319-331

The profiles of absolute current velocity obtained by using a lowered acoustic doppler current profiler (LADCP) are presented. In the course of the BSERP-3 expedition, the measurements were carried out in the regions of the Rim Current, anticyclonic eddy, and northwest shelf. In the core of the Rim Current, a unidirectional motion of waters is traced in layers below the main pycnocline down to depths greater than 500 m. Its characteristic velocity can be as high as 0.08 m/sec. It is shown that the direct action of the eddy is detected in the shelf region at distances larger than 20 km from the outer edge of the shelf in the zone bounded by an isobath of 100 m. The formation of multilayer vertical structures in the field of current velocities is revealed in the region of interaction of the anticyclonic eddy with irregularities of the bottom on the side of the shelf. A two-layer structure of currents with specific features in the layer of formed seasonal pycnocline is observed in the region of the shelf down to an isobath of 100 m. The profiles of the moduli of vertical shears of currents averaged over the casts ensemble are presented for the abyssal and shelf parts of the sea. It is shown that the shears induced by the geostrophic currents and wave processes in the region of the main pycnocline are comparable. Below the pycnocline, the shears are mainly determined by the wave processes. Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 25–37, November–December, 2008.  相似文献   

Sulfide intrusion in the tropical seagrasses Thalassia testudinum and Syringodium filiforme     

Marianne Holmer  Ole Pedersen  Dorte Krause-Jensen  Birgit Olesen  Malene Hedegrd Petersen  Stephanie Schopmeyer  Marguerite Koch  Bente Aa. Lomstein  Henning S. Jensen 《Estuarine, Coastal and Shelf Science》2009,85(2):319-326

Sulfur and oxygen dynamics in the seagrasses Thalassia testudinum and Syringodium filiforme and their sediments were studied in the US Virgin Islands (USVI) in order to explore sulfide intrusion into tropical seagrasses. Four study sites were selected based on the iron concentration in sediments and on proximity to anthropogenic nutrient sources. Meadow characteristics (shoot density, above- and below-ground biomass, nutrient content) were sampled along with sediment biogeochemistry. Sulfide intrusion was high in T. testudinum, as up to 96% of total sulfur in the plant was derived from sediment-derived sulfides. The sulfide intrusion was negatively correlated to the turnover of sulfides in the sediments regulated by both plant parameters and sediment sulfur pools. Sediment iron content played an indirect role by affecting sulfide turnover rates. Leaf production was negatively correlated with sulfide intrusion suggesting that active growth reduced sulfide intrusion. Sulfide intrusion was lower in S. filiforme (up to 44%) compared to T. testudinum consistent with a higher internal nighttime oxygen concentrations found for S. filiforme. When S. filiforme can take advantage of its ability to maintain high internal oxygen concentrations, as was the case on the USVI, it could increase its success in colonizing unvegetated disturbed sediments with potentially high sulfide concentrations.  相似文献   

Fe2+-Ti4+ charge transfer in stoichiometric Fe2+,Ti4+-minerals     

Stephanie M. Mattson  George R. Rossman 《Physics and Chemistry of Minerals》1988,16(1):78-82

Optical absorption spectra are presented for taramellite, traskite and neptunite, all of which have both Fe²⁺ and Ti⁴⁺ as major elements. The spectra of each of these minerals are dominated by a single, intense absorption band in the 415 to 460 nm region with 7000 to 9000 cm^?1 halfwidth. These transitions, assigned to Fe²⁺-Ti⁴⁺ intervalence charge transfer, showed little difference in intensity at 80 and 300 K and have molar absorptivities which range from ～100 to ～1300 M^?1 cm^?1. The Fe²⁺-Ti⁴⁺ absorptions in these standards generally compare well to other mineral spectra in which Fe²⁺ — Ti⁴⁺ intervalence absorption has previously been proposed with the exception of the most cited example, blue corundum.  相似文献   

Inverted-polarity electrical structures in thunderstorms in the Severe Thunderstorm Electrification and Precipitation Study (STEPS)     

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   

Traveltime measurements from noise correlation: stability and detection of instrumental time-shifts   总被引：1，自引：0，他引：1  

L. Stehly  M. Campillo  N. M. Shapiro 《Geophysical Journal International》2007,171(1):223-230

We test the feasibility of using Green's functions extracted from records of ambient seismic noise to monitor temporal changes in the Earth crust properties by repeated measurements at regional distances. We use about 11 yr of continuous recordings to extract surface waves between three pairs of stations in California. The correlations are computed in a moving 1-month window and we analyse the temporal evolution of measured interstation traveltimes. The comparison of the arrival times in the positive and negative correlation time of Rayleigh and Love waves allows us to separate time-shifts associated with any form of physical change in the medium, those resulting from clock drift or other instrumental errors, and those due to change in the localization of the noise sources. This separation is based on the principle of time symmetry. When possible, we perform our analysis in two different period bands: 5–10 and 10–20 s. The results indicate that significant instrumental time errors (0.5 s) are present in the data. These time-shifts can be measured and tested by closure relation and finally corrected independently of any velocity model. The traveltime series show a periodic oscillation that we interpret as the signature of the seasonal variation of the region of origin of the seismic noise. Between 1999 and 2005, the final arrival time fluctuations have a variance of the order of 0.01 s. This allows us to measure interstation traveltimes with errors smaller than 0.3 per cent of the interstation traveltime and smaller than 1 per cent of the used wave period. This level of accuracy was not sufficient to detect clear physical variation of crustal velocity during the considered 11 yr between the three stations in California. Such changes may be more easily detectable when considering pairs of stations more closely located to each other and in the vicinity of tectonically active faults or volcanoes.  相似文献   

Time-Relative Positioning with a Single Civil GPS Receiver     

Stephanie Michaud  Rock Santerre 《GPS Solutions》2001,5(2):71-77

Time-relative positioning is a recent method for processing GPS phase observations. The operational method undertaken in this paper consists of the following steps: first, recording phase observations at a station of known coordinates; second, moving the GPS receiver to an unknown station (which can be located up to a few hundred meters away, dependint on what type of transportation – e. g., walking, motorcycle – is available) while continuously observing carrier phases; and, third, recording phase observations at a second station of unknown coordinates with a single GPS receiver. To obtain the position of the unknown station relative to the first (known) station, the processing method uses combined observations taken at two different epochs and two different stations with the same receiver. For this reason, the errors that vary between two epochs must be taken into account in an appropriate way, especially errors in satellite clock corrections and ephemerides, and errors related to tropospheric and ionospheric delays. Ionospheric modeling using IONEX files (the ionospheric maps calculated by the International GPS Service) was also tested to correct L1 phase observations. This method has been used to calculate short vectors with an accuracy of a few centimeters (for a processing interval of 30 s) using a single civil GPS receiver. ? 2001 John Wiley & Sons, Inc.  相似文献   

Evidence of the dominance of higher-mode surface waves in the lake-bed zone of the Valley of Mexico     

N. M. Shapiro  S. K. Singh  D. Almora  M. Ayala 《Geophysical Journal International》2001,147(3):517-527

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Sources of Zircons from Cretaceous and Lower Paleogene Terrigenous Sequences of the Southern Koryak Upland and Western Kamchatka     

Shapiro  M. N.  Soloviev  A. V.  Garver  G. I.  Brandon  M. T. 《Lithology and Mineral Resources》2001,36(4):322-336

The mineral composition of sandstones from Cretaceous–Lower Paleocene terrigenous sequences of the western Kamchatka–Ukelayat zone (southern Koryak Upland, western Kamchatka) suggests that the Okhotsk–Chukot volcanogenic belt and fragments of the Uda–Murgal island arc served as the most probable provenance. Fission-track dating of zircon showed that sandstones from this zone contain detrital zircon of several different-age populations. Fission tracks in zircon grains were nor subjected to secondary ignition. The age of young zircon population coincides with the biostratigraphic age of host sequences. Thus, results of dating of detrital zircon grains from sandstones, which did not experience heating above 215–240°C, indicate that this method is appropriate for dating fossil-free terrigenous sequences. The young zircon population in the sandstones is related to erosion of plagiogranite and diorite intrusions of the Uda–Murgal arc and outer zone of the Okhotsk–Chukot volcanic belt exposed at the day surface owing to differential vertical movements and rapid exhumation of blocks.  相似文献   

Lunar baselines and libration from differential Vlbi observations of alseps     

C. C. Counselman III  H. F. Hinteregger  R. W. King  I. I. Shapiro 《Earth, Moon, and Planets》1973,8(4):484-489

Differential very-long-baseline interferometric observations of signals from Apollo Lunar Surface Experiment Package telemetry transmitters will yield the relative projected positions of the transmitters with uncertainty of only 1-3 m, set mainly by uncertainty of the lunar ephemeris. Noise and systematic instrumental errors which in the past affected similar observations have been reduced to the equivalent of a few centimeters on the lunar surface by the development of a new type of differential receiver. Continued observations should yield a determination of the motion of the Moon about its center of mass with uncertainty less than 1 s of selenocentric arc. Improvements (by other means) in our knowledge of the Moon's orbital motion would allow a further order-of-magnitude refinement in the libration and relative position results obtainable by differential VLBI.Communication presented at the conference on Lunar Dynamics and Observational Coordinate Systems held January 15–17, 1973 at the Lunar Science Institute, Houston, Tex. U.S.A.  相似文献   

Radar Observations of Asteroid 3908 Nyx     

Lance A.M. BennerSteven J. Ostro  R.Scott HudsonKeith D. Rosema  Raymond F. JurgensDonald K. Yeomans  Donald B. CampbellJohn F. Chandler  Irwin I. Shapiro 《Icarus》2002,158(2):379-388

We report Doppler-only (cw) radar observations of basaltic near-Earth asteroid 3908 Nyx obtained at Arecibo and Goldstone in September and October of 1988. The circular polarization ratio of 0.75±0.03 exceeds ∼90% of those reported among radar-detected near-Earth asteroids and it implies an extremely rough near-surface at centimeter-to-decimeter spatial scales. Echo power spectra over narrow longitudinal intervals show a central dip indicative of at least one significant concavity. Inversion of cw spectra yields two statistically indistinguishable shape models that have similar shapes and dimensions but pole directions that differ by ∼100°. We adopt one as our working model and explore its implications. It has an effective diameter of 1.0±0.15 km and radar and visual geometric albedos of 0.15±0.075 and 0.16^+0.08_−0.05. The visual albedo supports the interpretation by D. P. Cruikshank et al. (1991, Icarus89, 1-13) that Nyx has a thermal inertia consistent with that of bare rock. The model is irregular, modestly asymmetric, and topographically rugged.  相似文献