World Symposium on Spherics     

H. Israël 《Pure and Applied Geophysics》1953,25(1):223-224

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The Role of Laser Ranging for Calibrating Jason-1: The Corsica Tracking Campaign     

Pierre Exertier  Joë  lle Nicolas  Philippe Berio  David Coulot  Pascal Bonnefond  Olivier Laurain 《Marine Geodesy》2004,27(1):333-340

The French Transportable Laser Ranging System (FTLRS), a highly transportable Satellite Laser Ranging (SLR) instrument, was set up in Corsica (from January to September 2002) for participating to the JASON-1 altimeter verification phase. In addition to the tracking of oceanographic satellite missions and in order to perform an accurate positioning, the FTLRS also acquired laser ranging data on geodetic satellites, STARLETTE and STELLA essentially.

The paper describes the analysis strategy mainly based on the use of a short-arc orbit technique to compute accurate 1 cm local orbits, and then the geocentric positioning (2-3 mm relative to GPS). Finally, we established the JASON-1 absolute calibration value, based on 9 SLR short-arcs (between cycles 1 and 26), at 108.2 ± 8.7 mm; the 10-day repeatability is of 26.1 mm showing that a great accuracy has been reached.  相似文献   

Central kiloparsec of Seyfert and inactive host galaxies: a comparison of two-dimensional stellar and gaseous kinematics     

Gaëlle Dumas  Carole G. Mundell  Eric Emsellem  Neil M. Nagar 《Monthly notices of the Royal Astronomical Society》2007,379(4):1249-1278

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The 27-Day Signal in Sunspot Number Series and the Solar Dynamo     

Jean-Louis Le Mouël  Mikhail G. Shnirman  Elena M. Blanter 《Solar physics》2007,246(2):295-307

We analyze the Wolf number daily series WN (1849 to present) as well as two other related series characterizing solar activity. Our analysis consists in computing the amplitude of a given Fourier component in a sliding time window and examining its long-term evolution. We start with the well-known 27.03- and 27.6-day periods and observe strong decadal variations of this amplitude as well as a sharp increase of the average value starting around 1905. We then consider a packet of 31 lines with periods from 25.743 to 28.453 days, which is shown to be a better representation of the synodic solar rotation. We first examine the temporal evolution of individual lines, then the energy of the packet. The energy of the packet increases sharply at the beginning of the 20th century, leading by more than two decades the well-known increase of the Wolf number. The nonaxisymmetry of sunspots increases before the total increase of activity and may be considered as a precursor. We discuss briefly and tentatively this observation in terms of solar dynamo theory.  相似文献   

Seismically induced shale diapirism: the Mine d’Or section,Vilaine estuary,Southern Brittany     

B. Van Vliet-Lanoe  C. Hibsch  L. Csontos  S. Jegouzo  B. Hallégouët  M. Laurent  A. Maygari  D. Mercier  P. Voinchet 《International Journal of Earth Sciences》2009,98(5):969-984

The Pénestin section (southern Brittany) presents large regular undulations, commonly interpreted as evidence of periglacial pingos. It is an upper Neogene palaeoestuary of the Vilaine River reactivated during the middle Quaternary (middle terrace). It is incised into a thick kaolinitic saprolite and deformed by saprolite diapirs. This paper presents the arguments leading to a mechanistic interpretation of the deformations at Pénestin. Neither recent transpressive tectonics nor diagnostic evidence of periglacial pingo have been found despite evidence for a late paleo-permafrost. The major deformational process is shale diapirism, initially triggered by co-seismic water supply, with further loading and lateral spreading on an already deformed and deeply weathered basement, which allowed the shale diapirism to develop. Deformations are favoured by the liquefaction of the saprolite and a seaward mass movement and recorded, rather distant, effects of an earthquake (c. 280 ka B.P.) resulting from the progressive subsidence of the southern Armorican margin. These deformations triggered by an earthquake are similar to those induced by classical shale diapirism. They are probably common in tectonically active continental environments with shallow water table.  相似文献   

Sources of in-situ 36Cl in basaltic rocks. Implications for calibration of production rates     

Irene Schimmelpfennig  Lucilla Benedetti  Robert Finkel  Raphaël Pik  Pierre-Henri Blard  Didier Bourlès  Pete Burnard  Alice Williams 《Quaternary Geochronology》2009,4(6):441-461

In-situ cosmogenic ³⁶Cl production rates from spallation of Ca and K determined in several previously published calibration studies differ by up to 50%. In this study we compare whole rock ³⁶Cl exposure ages with ³⁶Cl exposure ages evaluated in Ca-rich plagioclase in the same 10 ± 3 ka lava sample taken from Mt. Etna (Sicily, 38° N). The exposure age of the sample was determined by K–Ar and corroborated by cosmogenic ³He measurements on cogenetic pyroxene phenocrysts. Sequential dissolution experiments showed that high Cl concentrations in plagioclase grains could be reduced from 450 ppm to less than 3 ppm after 16% dissolution. ³⁶Cl exposure ages calculated from the successive dissolution steps of this leached plagioclase sample are in good agreement with K–Ar and ³He age. Stepwise dissolution of whole rock grains, on the other hand, is not as effective in reducing high Cl concentrations as it is for the plagioclase. 330 ppm Cl still remains after 85% dissolution. The ³⁶Cl exposure ages derived are systematically about 30% higher than the ages calculated from the plagioclase. We could exclude contamination by atmospheric ³⁶Cl as an explanation for this overestimate. Magmatic ³⁶Cl was estimated by measuring a totally shielded sample, but was found to account for only an insignificant amount of ³⁶Cl in the case of the 10 ka whole rock sample. We suspect that the overestimate of the whole rock exposure age is due to the difficulty in accurately assessing all the factors which control production of ³⁶Cl by low-energy neutron capture on ³⁵Cl, particularly variable water content and variable snow cover. We conclude that some of the published ³⁶Cl spallation production rates might be overestimated due to high Cl concentrations in the calibration samples. The use of rigorously pretreated mineral separates reduces Cl concentrations, allowing better estimates of the spallation production rates.In the Appendix of this paper we document in detail the equations used. These equations are also incorporated into a ³⁶Cl calculation spreadsheet made available in the supplementary data.  相似文献   

Inhomogeneous distribution of REE in scheelite and dynamics of Archaean hydrothermal systems (Mt. Charlotte and Drysdale gold deposits, Western Australia)   总被引：5，自引：0，他引：5  

Joël Brugger  Yann Lahaye  Sylvie Costa  David Lambert  Roger Bateman 《Contributions to Mineralogy and Petrology》2000,139(3):251-264

Scheelite is a widespread accessory mineral in hydrothermal gold deposits, and its rare earth element (REE) patterns and Nd and Sr isotopic compositions can be used to constrain the path and origin of the mineralising fluids and the age of the hydrothermal activity. Micro-analyses by laser ablation high resolution inductively coupled mass spectroscopy and cathodoluminescence imaging reveal a very inhomogeneous distribution of the REE in single scheelite grains from the Mt. Charlotte and Drysdale Archaean gold deposits in Western Australia. Two end-member REE patterns are distinguished: type I is middle REE (MREE)-enriched, with no or minor positive Eu-anomaly, whereas type II is flat or MREE-depleted with a strong positive Eu-anomaly. The chemical inhomogeneity of these scheelites is related to oscillatory zoning involving type I and type II patterns, with zone widths varying from below 1 to 200 μm. Intra-sectorial growth discontinuities, syn-crystallisation brittle deformation, and variations in the relative growth velocities of crystallographically equivalent faces suggest a complex crystallisation history under dynamic hydraulic conditions. The co-existence of MREE-enriched and MREE-depleted patterns within single scheelite crystals can be explained by the precipitation of a mineral which strongly partitions MREE relative to light and heavy REE. Scheelite itself has such characteristics, as does fluorapatite, which is locally abundant and has REE contents similar to that of scheelite. In this context, the systematic increase of the Eu-anomaly between type I and type II patterns is produced by the difference between the partition coefficients of Eu²⁺ and Eu³⁺, and not by fluid mixing or redox reactions. Consequently, the high positive Eu-anomaly typical of scheelite from gold ores may not necessarily be inherited from the hydrothermal fluid, but may reflect processes occurring during ore deposition. This case study demonstrates that in hydrothermal systems characterised by low REE concentrations in the fluid, and by the precipitation of a REE-rich mineral which strongly fractionates the REE, the REE patterns of such a mineral will be highly sensitive to the dynamics of the hydrothermal system. Received: 1 November 1999 / Accepted: 4 February 2000  相似文献   

On decadal-scale ocean-atmosphere interactions in the extended ECHAM1/LSG climate simulation     

C. Frankignoul  E. Kestenare  N. Sennéchael  G. de Coëtlogon  F. D'Andrea 《Climate Dynamics》2000,16(5):333-354

 The last 810 years of a control integration with the ECHAM1/LSG coupled model are used to clarify the nature of the ocean-atmosphere interactions at low frequencies in the North Atlantic and the North Pacific. To a first approximation, the atmosphere acts as a white noise forcing and the ocean responds as a passive integrator. The sea surface temperature (SST) variability primarily results from short time scale fluctuations in surface heat exchanges and Ekman currents, and the former also damp the SST anomalies after they are generated. The thermocline variability is primarily driven by Ekman pumping. Because the heat, momentum, and vorticity fluxes at the sea surface are correlated in space and time, the SST variability is directly linked to that in the ocean interior. The SST is also modulated by the wind-driven geostrophic fluctuations, resulting in persistent correlation with the thermocline changes and a slight low-frequency redness of the SST spectra. The main dynamics are similar in the two oceans, although in the North Pacific the SST variability is more strongly influenced by advection changes and the oceanic time scales are larger. A maximum covariance analysis based on singular value decomposition in lead and lag conditions indicates that some of the main modes of atmospheric variability in the two oceans are sustained by a very weak positive feedback between the atmosphere, SST, and the strength of the subtropical and subpolar gyres. In addition, in the North Atlantic the main surface pressure mode has a small quasi-oscillatory component at 6-year period, and advective resonance occurs for SST around 10-year period, both periods being also singled out by multichannel singular spectrum analysis. The ocean-atmosphere coupling is however much too weak to redden the tropospheric spectra or create anything more than tiny spectral peaks, so that the atmospheric and oceanic variability is dominated in both ocean sectors by the one-way interactions. Received: 2 April 1999 / Accepted: 14 October 1999  相似文献   

Forecasting the energy produced by a windmill on a yearly basis     

Alain Bensoussan  Pierre Rapha?l Bertrand  Alexandre Brouste 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(8):1109-1122

The objective of this article is to study as extensively as possible the uncertainties affecting the annual energy produced by a windmill. In the literature, the general approach is to estimate the mean annual energy from a transformation of a Weibull distribution law. Then the issue is reduced to estimating the coefficients of this distribution. This is obtained by classical statistical methods. Therefore, the uncertainties are mostly limited to those resulting from the statistical procedures. But in fact, the real uncertainty of the random variable which represents the annual energy cannot been reduced to the uncertainty on its mean and to the uncertainties induced from the estimation procedure. We propose here a model, which takes advantage of the fact that the annual energy production is the sum of many random variables representing the 10?min energy production during the year. Under some assumptions, we make use of the central limit theorem and show that an intrinsic uncertainties of wind power, usually not considered, carries an important risk. We also explain an observation coming from practice that the forecasted annual production is always overestimated, which creates a risk of reducing the profitability of the operation.  相似文献   

Assessing the additive risks of PSII herbicide exposure to the Great Barrier Reef     

Lewis SE  Schaffelke B  Shaw M  Bainbridge ZT  Rohde KW  Kennedy K  Davis AM  Masters BL  Devlin MJ  Mueller JF  Brodie JE 《Marine pollution bulletin》2012,65(4-9):280-291

Herbicide residues have been measured in the Great Barrier Reef lagoon at concentrations which have the potential to harm marine plant communities. Monitoring on the Great Barrier Reef lagoon following wet season discharge show that 80% of the time when herbicides are detected, more than one are present. These herbicides have been shown to act in an additive manner with regards to photosystem-II inhibition. In this study, the area of the Great Barrier Reef considered to be at risk from herbicides is compared when exposures are considered for each herbicide individually and also for herbicide mixtures. Two normalisation indices for herbicide mixtures were calculated based on current guidelines and PSII inhibition thresholds. The results show that the area of risk for most regions is greatly increased under the proposed additive PSII inhibition threshold and that the resilience of this important ecosystem could be reduced by exposure to these herbicides.  相似文献