Stochastic Modeling of Short Term Variations of Sea Level in Eastern Canada     

Karim Hilmi  Mohammed I. El-Sabh  Jean-Pierre Chanut  Tad Murty 《Marine Geodesy》2013,36(3):197-218

Hourly sea level records from three stations in eastern Canada (Québec-Lauzon, Harrington-Harbour and Halifax) are analyzed both in frequency domain from 1970 to 1979 and in time domain during 1973. At the three stations, the deterministic model explains 90 to 96% of the total variability of sea level. The semidiurnal and diurnal tides contribute largely to its variations. The residual series, less than 10% of the initial variations of sea level, contain irregular values including extreme values of seiches and storm surges. Such random variations are analyzed and modeled following the method described by Box and Jenkins (1976). The long period variations (2 to 30 days) can be attributed to meteorological forcing (atmospheric pressure and winds). The short period variations (some hours to one day) can be attributed to longitudinal seiches, semidiurnal and diurnal atmospheric tides, and inertial oscillations. The water discharge from the St. Lawrence River contributes 29% of the monthly residual sea level at Qué  相似文献   

The thermal evolution of Mars as constrained by paleo-heat flows     

Javier Ruiz  Patrick J. McGovern  Valle López  Jean-Pierre Williams  Rosa Tejero 《Icarus》2011,215(2):508-517

Lithospheric strength can be used to estimate the heat flow at the time when a given region was deformed, allowing us to constrain the thermal evolution of a planetary body. In this sense, the high (>300 km) effective elastic thickness of the lithosphere deduced from the very limited deflection caused by the north polar cap of Mars indicates a low surface heat flow for this region at the present time, a finding difficult to reconcile with thermal history models. This has started a debate on the current heat flow of Mars and the implications for the thermal evolution of the planet. Here we perform refined estimates of paleo-heat flow for 22 martian regions of different periods and geological context, derived from the effective elastic thickness of the lithosphere or from faulting depth beneath large thrust faults, by considering regional radioactive element abundances and realistic thermal conductivities for the crust and mantle lithosphere. For the calculations based on the effective elastic thickness of the lithosphere we also consider the respective contributions of crust and mantle lithosphere to the total lithospheric strength. The obtained surface heat flows are in general lower than the equivalent radioactive heat production of Mars at the corresponding times, suggesting a limited contribution from secular cooling to the heat flow during the majority of the history of Mars. This is contrary to the predictions from the majority of thermal history models, but is consistent with evidence suggesting a currently fluid core, limited secular contraction for Mars, and recent extensive volcanism. Moreover, the interior of Mars could even have been heating up during part of the thermal history of the planet.  相似文献   

A space Fresnel Imager for ultra-violet astrophysics: example on accretion disks     

Truswin Raksasataya  Ana-Ines Gomez de Castro  Laurent Koechlin  Jean-Pierre Rivet 《Experimental Astronomy》2011,30(2-3):183-194

The Fresnel Diffractive Imager concept is proposed for space borne astronomical imaging at Ultra-Violet wavelengths, using diffractive focalization. The high angular resolution and high dynamic range provided by this new concept makes it an ideal tool to resolve circumstellar structures such as disks or jets around bright sources, among them, pre-main sequence stars and young planetary disks. The study presented in this paper addresses the following configuration of Fresnel diffractive imager: a diffractive array 4 m large, with 696 Fresnel zones operating in the ultra-violet domain. The diffractive arrays are opaque foils punched with a large number of void subapertures with carefully designed shapes and positions. In the proposed space missions, these punched foils would be deployed in space. Depending on the size of the array and on the working spectral band, the focal length of such imagers will range from a few kilometers to a few tens of kilometers. Thus, such space mission requires a formation flying configuration for two satellites around the L2 Sun-Earth Lagragian point. In this article, we investigate numerically the potential of Fresnel arrays for imaging circumstellar dust environments. These simulations are based upon simple protostellar disk models, and on the computed optical characteristics of the instrument. The results show that protoplanetary disks at distances up to a few thousand parsecs can be successfully studied with a 4 m aperture Fresnel imager in the UV.  相似文献   

Crystal chemistry of suspended matter in a tropical hydrosystem, Nyong basin (Cameroon, Africa)     

Gwenaelle Olivi  -Lauquet  Thierry Allard  Jacques Bertaux  Jean-Pierre Muller 《Chemical Geology》2000,170(1-4):113-131

Suspended matter (SM) from the Nyong basin (Cameroon, Africa), a tropical watershed, was collected by tangential flow ultrafiltration to separate particulate (>0.45 μm) and colloidal (<0.45 μm; >20 kDa) fractions. In this basin, two distinctive systems in a selected small catchment (Nsimi–Zoétélé) of the Nyong river basin have been considered: (i) colourless water (groundwater and spring) with a low suspended load (<3 mg/l) and a low total organic carbon content (TOC<1 mg/l) and (ii) coloured water (Mengong brook and Nyong river), which is organic rich (TOC>10 mg/l) and contains higher amounts of SM (10–20 mg/l) than the colourless water. Freeze-dried samples of SM have been analysed by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), electron paramagnetic resonance spectroscopy (EPR), and visible diffuse reflectance spectroscopy (DRS).

Colourless water mainly contains mineral phases, such as poorly ordered kaolinite, plus quartz and goethite in the particulate fraction, and euhedral kaolinite plus amorphous iron oxyhydroxides in the colloidal fraction. In contrast, the SM in coloured water is mainly organic in nature. The mineral phases in the particulate fraction are similar to those from clear water, but with additional phytoliths and diatom frustules composed of biogenic opal. In the colloidal fraction, complexation of Fe³⁺ and Mn²⁺ with organic matter is evidenced by EPR, together with significant occurrence of Fe oxyhydroxides associated with organic matter.

The sites of Al, Si, Fe, Mn in colloidal fractions derived from spectroscopic analyses are discussed with reference to chemical analyses performed by inductively coupled plasma mass spectrometry. Most of the observed solid phases or species correspond to those expected from published thermodynamic calculations for the same hydrosystem, except the colloidal iron oxyhydroxides in the coloured water. The presence of such iron phases is emphasised since they are expected to have large sorption capacities for numerous trace elements.

The crystal chemistry of SM is used to discuss the origin of the mineral particles transported from the soil to the main rivers in terms of mechanical and chemical erosion processes.  相似文献   

Correlated fast time structures at millimeter waves and hard X-rays during a solar burst     

Kaufmann  P.  Trottet  G.  Giménez de Castro  C.G.  Costa  J.E.R.  Raulin  J.-P.  Schwartz  R.A.  Magun  A. 《Solar physics》2000,197(2):361-374

We present an analysis of the time profiles detected during a solar impulsive flare, observed at one-millimeter radio frequency (48 GHz) and in three hard X-ray energy bands (25–62, 62–111, and 111–325 keV) with high sensitivity and time resolution. The time profiles of all emissions exhibit fast time structures of 200–300 ms half power duration which appear in excess of a slower component varying on a typical time scale of 10 s. The amplitudes of both the slow and fast variations observed at 48 GHz are not proportional to those measured in the three hard X-ray energy bands. However, the fast time structures detected in both domains are well correlated and occur simultaneously within 64 ms, the time resolution of the hard X-ray data. In the context of a time-of-flight flare model, our results put strong constraints on the acceleration time scales of electrons to MeV energies.  相似文献   

喜马拉雅的两个造山体系和一个转换-转移断层:证据及推论   总被引：1，自引：0，他引：1  

Jean-Pierre BURG 《地学前缘》2006,13(4):27-46

位于中喜马拉雅和巴基斯坦境内西喜马拉雅的两个相互结合的剖面在一级单元、断层中展现出不同的构造形式;并在不同时期,以不同速率发育了二级构造。沿两剖面岩性单元的显著差异显示通常指的圆柱状喜马拉雅带并没有越过喀喇昆仑山断层。与此同时,在近来许多区域研究中显示出来的构造轮廓强调主中央逆冲断层是一个貌似与中喜马拉雅断层带和越过西部山脉的西喜马拉雅断层带有联系的独立部分。上述两个地区展现出不同的碰撞历史。这些不同之处揭示喀喇昆仑山断层是西部岛弧保留造山带与东部岛弧俯冲造山带之间转移/转换断层的再活动或衍变。  相似文献   

Extension et sédimentation au paléozoïque terminal et au Mésozoïque dans le bassin de Majunga (Nord-Ouest de Madagascar)     

Yolande Razafindrazaka  Thogne Randriamananjara  Alain Piqu  Catherine Thouin  Edgard Laville  Jacques Malod  Jean-Pierre Rhault 《Journal of African Earth Sciences》1999,28(4):949-959

The Majunga Basin is located in the northwestern part of Madagascar with a N45–60°E trending axis. It was filled by almost exclusively continental Karoo Supergroup sediments, which are Permian to Early Jurassic in age, and by younger sequences, mainly marine, that were deposited from the Middle Jurassic to the present.The Karoo Basin geometry is deduced from the analysis of seismic sections. A central northeast trending horst is flanked by two sub-basins. Deposition of the Karoo sequences was controlled by these northeast trending faults. On the contrary, the Middle Jurassic to present sequences witness only a slight tilting of the basement towards the northwest.The development of the Majunga Basin includes, therefore, two successive stages. In the synrift episode, from Permian to Early Jurassic times, the sedimentation was syntectonic, controlled by synsedimentary faulting and the creation of a horst and graben extensive pattern. The postrift episode started during the Middle Jurassic.These two stages of the Majunga Basin development correspond to the geodynamic evolution recorded elsewhere in this part of the Gondwana.  相似文献   

Intertidal clay-drape couplets (Gironde estuary, France)     

Hugues Fenies  Amaury De Resseguier  & Jean-Pierre Tastet 《Sedimentology》1999,46(1):1-15

Clay-drape couplets on subaqueous dunes have been regarded as a diagnostic feature of the subtidal environment since Visser's seminal paper (1980). The new observation of clay-drape couplets in the intertidal zone on a present day tidal bar of the Gironde estuary shows that they are not restricted to the subtidal zone.
In the intertidal zone, low-tide slack-water clay drapes are deposited in the bottomsets of the dominant current dunes when the muddy water retained in the troughs is absorbed into the sand during the emergence of the intertidal bar. They drape emergence run-off ripples generated by the drainage currents in the bottomsets. High-tide slack-water clay drapes are deposited over the entire dune surface and are preserved on the lee side of the dunes and in the bottomsets. They drape the subordinate current ripples. Low-tide and high-tide slack-water clay drapes enclose one thin rippled sand layer (the subordinate current bundle) and are isolated from other adjacent clay-drape couplets by the dominant current bundle.
The clay-drape couplets deposited in the intertidal zone can be distinguished from their subtidal counterparts on the basis of two morphological differences:
1. In the intertidal zone, the low-tide clay drape is only present in the bottomsets of the dunes, whereas in the subtidal zone equivalent clay drapes are also present on the lower part of the lee side of the dunes.
2. In the intertidal zone, low-tide clay drapes are deposited in the bottomsets of the dunes over emergence run-off ripples oriented in the direction of the drainage currents (i.e. in a direction normal to the tidal currents). Conversely, in the subtidal zone, the equivalent clay drapes are typically deposited over ripples oriented in the tidal-current direction (ebb or flood). There is a difference of polarity of 90° between the intertidal and subtidal small-scale bedforms draped by the low-tide slack-water drapes.  相似文献   

Facies and architecture of an estuarine tidal bar (the Trompeloup bar, Gironde Estuary, SW France)   总被引：1，自引：0，他引：1  

Hugues Fenies  Jean-Pierre Tastet 《Marine Geology》1998,150(1-4):149-169

This study describes the sedimentary facies and internal architecture of a modern estuarine tidal bar present in the bay-head delta of a wave- and tide-dominated estuary, the Gironde Estuary, in southwest France. Based on 51 cores (2 to 5 m long), this work demonstrates that such bars are composite sedimentary bodies made up of individual sigmoidal sand units isolated from one another by thick muddy layers. The bar appeared in the study area around 1874. Since then, its evolution has been characterized by phases of rapid downstream bar migration alternating with periods of bar abandonment. During the periods of active bar progradation, which commonly last between 10 and 20 years, the bar progrades up to 7 km seaward and forms a narrow (200–800 m wide) sand ridge up to 6 m thick. During abandonment phases which also last around 10–20 years, the bar is starved of sand and a mud layer (1 to 3 m thick) is deposited. The vertical succession formed by the seaward progradation of the tidal bar records these alternating phases of growth and abandonment. A typical vertical succession in the bar system is 8 m thick and comprises several superimposed, upward-coarsening units of cross-stratified sand, deposited during phases of seaward progradation, separated by a thick layer of thinner-bedded mud and sand laminae deposited during phases of bar abandonment. When a tidal bar builds up to the supratidal zone, marshes accumulate and the bar becomes a permanent island in the estuary. The large-scale architecture of the bar is thus made of an alternation of potential sandy reservoir units and muddy internal seals. The reservoir units are characterized by a sigmoidal shape. The muddy layer, which is deposited between the two sigmoidal units, is a thick, continuous potential internal seal. This complex internal architecture is due to the fact that there is a considerable amount of mud present in the bay-head delta of the Gironde Estuary. It is thought to be representative of the architecture of tidal bars in the inner part of wave- and tide-dominated estuaries.  相似文献   

粤北晚泥盆世天子岭组遗迹组构及其环境解释   总被引：1，自引：0，他引：1  

齐永安  胡斌  Bruno Mistiaen 《煤田地质与勘探》2005,33(2):11-14

遗迹组构是由生物成因改造的沉积岩组构,它是物理过程和生物过程相互作用的产物。本文在广东韶关晚泥盆世天子岭组碳酸盐岩沉积中建立了4个遗迹组构,即反映局限台地或封闭海湾环境的Planolies montanus遗迹组构,反映台地潮下低能环境的Thalassinoides—Planolites遗迹组构,反映潮上-潮间环境的．Skolithos遗迹组构和受固底底质控制的Thalassinoides遗迹组构。对遗迹化石和生物扰动构造进行阶层分析,从中识别出受固底底质控制的遗迹化石Thalassinoides.sp,这类遗迹化石常常代表层序地层学中的重要界面。  相似文献