SMOS reveals the signature of Indian Ocean Dipole events     

Fabien Durand  Gaël Alory  Raphaël Dussin  Nicolas Reul 《Ocean Dynamics》2013,63(11-12):1203-1212

The tropical Indian Ocean experiences an interannual mode of climatic variability, known as the Indian Ocean Dipole (IOD). The signature of this variability in ocean salinity is hypothesized based on modeling and assimilation studies, on account of scanty observations. Soil Moisture and Ocean Salinity (SMOS) satellite has been designed to take up the challenge of sea surface salinity remote sensing. We show that SMOS data can be used to infer the pattern of salinity variability linked with the IOD events. The core of maximum variability is located in the central tropical basin, south of the equator. This region is anomalously salty during the 2010 negative IOD event, and anomalously fresh during the 2011 positive IOD event. The peak-to-peak anomaly exceeds one salinity unit, between late 2010 and late 2011. In conjunction with other observational datasets, SMOS data allow us to draw the salt budget of the area. It turns out that the horizontal advection is the main driver of salinity anomalies. This finding is confirmed by the analysis of the outputs of a numerical model. This study shows that the advent of SMOS makes it feasible the quantitative assessment of the mechanisms of ocean surface salinity variability in the tropical basins, at interannual timescales.  相似文献   

Null Variance Altitudes for the photolysis rate constants of species with barometric distribution: Illustration on Titan upper atmosphere modeling     

Zhe Peng  Fabien Cailliez  Michel Dobrijevic  Pascal Pernot 《Icarus》2012,218(2):950-955

The precision of the rates of the photolysis processes initiating the complex chemistry of Titan’s upper atmosphere conditions strongly the predictivity of photochemical models. Recent studies in sensitivity analysis of such models point out photolysis rate constants as key parameters. However, they have been treated approximately so far. We deal here directly with uncertainty in the absorption cross-sections to derive the uncertain altitude-dependent photolysis rate constants. We observe that the uncertainty on the photolysis rate constants of the major species, N₂ and CH₄, varies strongly with altitude and rather surprisingly vanishes at specific altitudes. We propose a simple model to interpret these features and we demonstrate that they are transferable to any major absorber distributed barometrically in an atmosphere.  相似文献   

Optical extinction due to aerosols in the upper haze of Venus: Four years of SOIR/VEX observations from 2006 to 2010     

Valérie Wilquet  Rachel Drummond  Arnaud Mahieux  Séverine Robert  Ann Carine Vandaele  Jean-Loup Bertaux 《Icarus》2012,217(2):875-881

The variability of the aerosol loading in the mesosphere of Venus is investigated from a large data set obtained with SOIR, a channel of the SPICAV instrument suite onboard Venus Express. Vertical profiles of the extinction due to light absorption by aerosols are retrieved from a spectral window around 3.0 μm recorded in many solar occultations (～200) from September 2006 to September 2010. For this period, the continuum of light absorption is analyzed in terms of spatial and temporal variations of the upper haze of Venus. It is shown that there is a high short-term (a few Earth days) and a long-term (～80 Earth days) variability of the extinction profiles within the data set. Latitudinal dependency of the aerosol loading is presented for the entire period considered and for shorter periods of time as well.  相似文献   

Nano dust impacts on spacecraft and boom antenna charging     

Filippo Pantellini  Soraya Belheouane  Nicole Meyer-Vernet  Arnaud Zaslavsky 《Astrophysics and Space Science》2012,341(2):309-314

High rate sampling detectors measuring the potential difference between the main body and boom antennas of interplanetary spacecraft have been shown to be efficient means to measure the voltage pulses induced by nano dust impacts on the spacecraft body itself (see Meyer-Vernet et al. in Sol. Phys. 256:463, 2009). However, rough estimates of the free charge liberated in post impact expanding plasma cloud indicate that the cloud’s own internal electrostatic field is too weak to account for measured pulses as the ones from the TDS instrument on the STEREO spacecraft frequently exceeding 0.1 V/m. In this paper we argue that the detected pulses are not a direct measure of the potential structure of the plasma cloud, but are rather the consequence of a transitional interruption of the photoelectron return current towards the portion of the antenna located within the expanding cloud.  相似文献   

Ab initio investigation into the elasticity of ultrahigh-pressure phases of SiO2     

Arnaud Metsue  Taku Tsuchiya 《Physics and Chemistry of Minerals》2012,39(3):177-187

In this study, we report the elastic properties of three ultrahigh-pressure phases of SiO₂: pyrite, cotunnite and Fe₂P types between 300 and 1,500 GPa calculated by means of the density functional ab initio method. It is generally thought that materials tend to be more compact and isotropic with increasing pressure. These three ultrahigh-pressure phases of silica are mechanically stable in the investigated pressure range according to the Born criteria, while the cotunnite and Fe₂P types are unstable at lower pressure. The elastic azimuthal anisotropy of these ultrahigh-pressure phases of silica shows that all the structures counterintuitively have considerable anisotropies even at multimegabar pressures. Among the three investigated structures, the cotunnite type of SiO₂ is the most elastically anisotropic phase due to a soft compression along the b axis combined with a large distortion of the polyhedrons that make the structure. This might also be related to its thermodynamic unfavorability compared to the Fe₂P type under extreme pressure condition. The bond property analyses clearly show that the Si–O bond remains an ionic-covalent mixed bond even at multimegabar pressures with an invariable ionicity with pressure. This argument can explain the monotonously pressure dependence of the elastic anisotropy in the case of pyrite, while the changes in the velocity distribution patterns out of the thermodynamic instability range largely contribute to those of the cotunnite and Fe₂P types.  相似文献   

GGR Biennial Critical Review: Analytical Developments Since 2010     

Michael Wiedenbeck  Roxana Bugoi  M. John M. Duke  Tibor Dunai  Jacinta Enzweiler  Mary Horan  Klaus Peter Jochum  Kathryn Linge  Jan Košler  Silke Merchel  Luiz F.G. Morales  Lutz Nasdala  Roland Stalder  Paul Sylvester  Ulrike Weis  Arnaud Zoubir 《Geostandards and Geoanalytical Research》2012,36(4):337-398

Advances in the chemical and isotopic characterisation of geological and environmental materials can often be ascribed to technological improvements in analytical hardware. Equally, the creation of novel methods of data acquisition and interpretation, including access to better reference materials, can also be crucial components enabling important breakthroughs. This biennial review highlights key advances in either instrumentation or data acquisition and treatment, which have appeared since January 2010. This review is based on the assessments by scientists prominent in each of the given analytical fields; it is not intended as an exhaustive summary, but rather provides insight from experts of the most significant advances and trends in their given field of expertise. In contrast to earlier reviews, this presentation has been formulated into a unified work, providing a single source covering a broad spectrum of geoanalytical techniques. Additionally, some themes that were not previously emphasised, in particular thermal ionisation mass spectrometry, accelerator‐based methods and vibrational spectroscopy, are also presented in detail.  相似文献   

Modelling the global ocean tides: modern insights from FES2004   总被引：30，自引：2，他引：30  

Florent Lyard  Fabien Lefevre  Thierry Letellier  Olivier Francis 《Ocean Dynamics》2006,56(5-6):394-415

During the 1990s, a large number of new tidal atlases were developed, primarily to provide accurate tidal corrections for satellite altimetry applications. During this decade, the French tidal group (FTG), led by C. Le Provost, produced a series of finite element solutions (FES) tidal atlases, among which FES2004 is the latest release, computed from the tidal hydrodynamic equations and data assimilation. The aim of this paper is to review the state of the art of tidal modelling and the progress achieved during this past decade. The first sections summarise the general FTG approach to modelling the global tides. In the following sections, we introduce the FES2004 tidal atlas and validate the model against in situ and satellite data. We demonstrate the higher accuracy of the FES2004 release compared to earlier FES tidal atlases, and we recommend its use in tidal applications. The final section focuses on the new dissipation term added to the equations, which aims to account for the conversion of barotropic energy into internal tidal energy. There is a huge improvement in the hydrodynamic tidal solution and energy budget obtained when this term is taken into account.  相似文献   

Fluid-dynamics driving saline water in the North East German Basin   总被引：2，自引：0，他引：2  

Fabien Magri  Ulf Bayer  Christoph Jahnke  V. Clausnitzer  H. J. Diersch  J. Fuhrman  P. Möller  A. Pekdeger  M. Tesmer  H. J. Voigt 《International Journal of Earth Sciences》2005,94(5-6):1056-1069

In several areas of the North German Basin, saline water comes close to, or even reaches the surface. Available data from wells indicate that brine stratification is under unstable conditions in the deeper underground. In order to analyse the possible transport mechanisms, 3D thermohaline simulations have been carried out for two different scenarios. The 3D regional model (230×330 km) indicates that salty water is driven to the surface by hydrostatical forces from the surrounding highlands. In addition, a smaller scale model (10×10 km) has been constructed with a grid resolution accounting for possible convective flow. The results indicate that convective flow may play a dominant role in areas with minor topography. In summary, the complex pattern of near surface occurrences of saline water probably results from the interaction of hydrostatic and thermal forces.  相似文献   

Tectonic evolution of the Dabieshan orogen: In the view from polyphase deformation of the Beihuaiyang metamorphic zone   总被引：1，自引：0，他引：1  

LIN Wei    Faure Michel  WANG Qingchen & Arnaud Nicolas . LTE  Institute of Geology  Geophysics  Chinese Academy of Sciences  Beijing  China  . Department of Earth  Planetary Sciences  Graduate School of Science  Nagoya University  Japan  . ISTO  UMR CNRS  Batiment Géosciences  Orléans Université d’Orléans  Orléans Cedex  France  . UMR "Magmas et Volcans"  Rue Kessler  Clermont-Ferrand  France 《中国科学D辑(英文版)》2005,48(7)

The Dabieshan and its geological counterpart in the Sulu area represent the eastern part of the Qinling-Dabie orogenic belt in Eastern China. This Orogen corresponds to the collision zone between the North and South China blocks (denoted as NCB and SCB, respectively) during the Early Mesozoic. Since the discovery of ultra-high-pressure (UHP) metamor- phism[1?3], research of the Dabieshan has made great progress from petrological work (e.g. Cong and Wang, 1999 and enclosed references)[…  相似文献   

How to anchor hotspots in a convecting mantle?     

Anne Davaille  Fabien GirardMichael Le Bars 《Earth and Planetary Science Letters》2002,203(2):621-634

Laboratory experiments were performed to study the influence of density and viscosity layering on the formation and stability of plumes. Viscosity ratios ranged from 0.1 to 6400 for buoyancy ratios between 0.3 and 20, and Rayleigh numbers between 10⁵ and 2.10⁸. The presence of a chemically stratified boundary layer generates long-lived thermochemical plumes. These plumes first develop from the interface as classical thermal boundary layer instabilities. As they rise, they entrain by viscous coupling a thin film of the other layer and locally deform the interface into cusps. The interfacial topography and the entrainment act to further anchor the plumes, which persist until the chemical stratification disappears through entrainment, even for Rayleigh numbers around 10⁸. The pattern of thermochemical plumes remains the same during an experiment, drifting only slowly through the tank. Scaled to an Earth’s mantle without plate tectonics, our results show that: (1) thermochemical plumes are expected to exist in the mantle, (2) they could easily survive hundreds of millions of years, depending on the size and magnitude of the chemical heterogeneity on which they are anchored, and (3) their drift velocity would be at most 1-2 mm/yr. They would therefore produce long-lived and relatively fixed hotspots on the lithosphere. However, the thermochemical plumes would follow any large scale motion imposed on the chemical layer. Therefore, the chemical heterogeneity acts more as a ‘floating anchor’ than as an absolute one.  相似文献