L'âge radiométrique du Miocène inférieur en Europe Occidentale et Centrale     

G. S. Odin  J. C. Hunziker  C. R. Lorenz 《International Journal of Earth Sciences》1975,64(1):570-592

Systematic research over years on datable horizons of lower Miocene age has led to an election of nine glauconite samples suitable for dating work. The chosen glauconites come from various regions of the tethys. Following careful sedimentological as well as stratigraphical studies the K-Ar ages of these glauconites were measured. The interpretation of the apparent ages found takes into consideration sedimentation, mineralogical quality and present knowledge of the genesis of the green glauconite pellets. The presented data allow to fix the basis of the Miocene at about 21–22 m. y. and the boundary of Aquitanian-Burdigalian at 18 m. y. The K-Ar data on glauconites presented here are in good agreement with newer measurements of other authors on high temperature minerals of the same age span.  相似文献   

Detailed observational study of a weak Echo region     

Stephan P. Nelson  Roscoe R. Braham Jr. 《Pure and Applied Geophysics》1975,113(1):735-746

High resolution 3-cm weather radar was used to observe the three dimensional structure of a weak echo region of a severe convective storm in northern Minnesota, U.S.A. Observations show that a seemingly steady-state updraft in the lower portion of the storm broke into an unsteady structure in the upper levels. This is interpreted as indicating that precipitation loading gradually decelerated the upper reaches of the updraft, resulting in periodic breakout of a new updraft core on the inflow side. This periodic behavior of the updraft may be related to hailstreaks and what has been termed the multi-celled storm.  相似文献   

Novel photosensors for neutrino detectors and telescopes     

Daniel Ferenc  Eckart Lorenz 《Earth, Moon, and Planets》2007,100(3-4):241-257

The volume and the photosensitive area of next generation detectors of the numerous rarely occurring phenomena will greatly exceed the sizes of the current experiments. These phenomena include cosmic neutrinos, atmospheric neutrinos, long-baseline neutrino beams from accelerators, geo-neutrinos, geo-reactor neutrinos, and hypothetic proton decays. Similar requirements hold for a new type of a large scanning device for homeland security and nuclear proliferation control, and for the future widely accessible medical imaging devices. Photon detectors are the most important component of such detectors. Existing photosensors are based on vacuum tubes and dynode electron multipliers that are essentially hand-made, expensive and nearly impossible to produce in large enough quantities. Silicon detectors are too small for experiments requiring a very large photosensitive area. Our laboratory is developing novel detectors with a large photosensitive area that can be mass-produced, similar to large flat panel TV displays.  相似文献   

Hydrocarbon lakes on Titan     

Giuseppe Mitri  Adam P. Showman  Ralph D. Lorenz 《Icarus》2007,186(2):385-394

The Huygens Probe detected dendritic drainage-like features, methane clouds and a high surface relative humidity (∼50%) on Titan in the vicinity of its landing site [Tomasko, M.G., and 39 colleagues, 2005. Nature 438, 765-778; Niemann, H.B., and 17 colleagues, 2005. Nature 438, 779-784], suggesting sources of methane that replenish this gas against photo- and charged-particle chemical loss on short (10-100) million year timescales [Atreya, S.K., Adams, E.Y., Niemann, H.B., Demick-Montelara, J.E., Owen, T.C., Fulchignoni, M., Ferri, F., Wilson, E.H., 2006. Planet. Space Sci. In press]. On the other hand, Cassini Orbiter remote sensing shows dry and even desert-like landscapes with dunes [Lorenz, R.D., and 39 colleagues, 2006a. Science 312, 724-727], some areas worked by fluvial erosion, but no large-scale bodies of liquid [Elachi, C., and 34 colleagues, 2005. Science 308, 970-974]. Either the atmospheric methane relative humidity is declining in a steady fashion over time, or the sources that maintain the relative humidity are geographically restricted, small, or hidden within the crust itself. In this paper we explore the hypothesis that the present-day methane relative humidity is maintained entirely by lakes that cover a small part of the surface area of Titan. We calculate the required minimum surface area coverage of such lakes, assess the stabilizing influence of ethane, and the implications for moist convection in the atmosphere. We show that, under Titan's surface conditions, methane evaporates rapidly enough that shorelines of any existing lakes could potentially migrate by several hundred m to tens of km per year, rates that could be detected by the Cassini orbiter. We furthermore show that the high relative humidity of methane in Titan's lower atmosphere could be maintained by evaporation from lakes covering only 0.002-0.02 of the whole surface.  相似文献   

Evidence for enhanced hydration on the northern flank of Olympus Mons, Mars     

Giancarlo Bellucci  Joern Helbert  Francesca Altieri  Dennis Reiss  Jean-Pierre Bibring  Stephan van Gasselt  Harald Hoffmann  Yves Langevin  Gerhard Neukum  Franois Poulet 《Icarus》2007,192(2):361-377

In this paper we report about a small region on the northern scarp of Olympus Mons showing an increase of the 3 μm hydration band in the OMEGA spectra, together with low superficial temperatures. Although water ice clouds can occurs on the flank of big martian volcanoes, radiative transfer modeling indicates that atmospheric water ice alone cannot justify the shape of the observed band. A fit of the 1.9–3 μm absorption features is obtained by hypothesizing that the study region consists of a mixture of dust and water ice covered by an optically thin (τ=0.08 at 3 μm) layer of dust. Thermal modeling also suggests that water ice in this region may be stable during most of the martian year due to the saturation of the atmosphere. If water ice is responsible for the observed spectral behavior, it might consist of a number of ice or snow patches possibly deposited in small depressions.  相似文献   

Technologies for adaptation to climate change. Examples from the agricultural and water sectors in Lebanon     

Sara Trærup  Jean Stephan 《Climatic change》2015,131(3):435-449

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Cassini SAR, radiometry, scatterometry and altimetry observations of Titan’s dune fields     

A. Le Gall  M.A. Janssen  A.G. Hayes  C. Savage  R.D. Lorenz  R.L. Kirk  S. Wall  E.R. Stofan  the Cassini Radar Team 《Icarus》2011,213(2):608-624

Large expanses of linear dunes cover Titan’s equatorial regions. As the Cassini mission continues, more dune fields are becoming unveiled and examined by the microwave radar in all its modes of operation (SAR, radiometry, scatterometry, altimetry) and with an increasing variety of observational geometries. In this paper, we report on Cassini’s radar instrument observations of the dune fields mapped through May 2009 and present our key findings in terms of Titan’s geology and climate. We estimate that dune fields cover ∼12.5% of Titan’s surface, which corresponds to an area of ∼10 million km², roughly the area of the United States. If dune sand-sized particles are mainly composed of solid organics as suggested by VIMS observations (Cassini Visual and Infrared Mapping Spectrometer) and atmospheric modeling and supported by radiometry data, dune fields are the largest known organic reservoir on Titan. Dune regions are, with the exception of the polar lakes and seas, the least reflective and most emissive features on this moon. Interestingly, we also find a latitudinal dependence in the dune field microwave properties: up to a latitude of ∼11°, dune fields tend to become less emissive and brighter as one moves northward. Above ∼11° this trend is reversed. The microwave signatures of the dune regions are thought to be primarily controlled by the interdune proportion (relative to that of the dune), roughness and degree of sand cover. In agreement with radiometry and scatterometry observations, SAR images suggest that the fraction of interdunes increases northward up to a latitude of ∼14°. In general, scattering from the subsurface (volume scattering and surface scattering from buried interfaces) makes interdunal regions brighter than the dunes. The observed latitudinal trend may therefore also be partially caused by a gradual thinning of the interdunal sand cover or surrounding sand sheets to the north, thus allowing wave penetration in the underlying substrate. Altimetry measurements over dunes have highlighted a region located in the Fensal dune field (∼5° latitude) where the icy bedrock of Titan is likely exposed within smooth interdune areas. The hemispherical assymetry of dune field properties may point to a general reduction in the availability of sediments and/or an increase in the ground humidity toward the north, which could be related to Titan’s asymmetric seasonal polar insolation. Alternatively, it may indicate that either the wind pattern or the topography is less favorable for dune formation in Titan’s northern tropics.  相似文献   

Sulfates and iron oxides in Ophir Chasma, Mars, based on OMEGA and CRISM observations     

Lorenz Wendt  Christoph Gross 《Icarus》2011,213(1):86-191

We investigate the sulfate and iron oxide deposits in Ophir Chasma, Mars, based on short-wave infrared data from the Compact Reconnaissance Imaging Spectrometer for Mars - CRISM and from the Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité - OMEGA. Sulfates are detected mainly in two locations. In the valley between Ophir Mensa and the southern wall of Ophir Chasma, kieserite is found both within the slope of Ophir Mensa, and superposed on the basaltic wall of the chasm. Here, kieserite is unconformably overlain by polyhydrated sulfate deposits and iron oxides. Locally, jarosite and unidentified phases with absorptions at 2.21 μm or 2.23 μm are detected, which could be mixtures of jarosite and amorphous silica or other poorly crystalline phases.The second large sulfate-rich outcrop is found on the floor of the central valley. Although the same minerals are found here, polyhydrated sulfates, kieserite, iron oxides, and locally a possibly jarosite-bearing phase, this deposit is very distinct. It is not layered, almost horizontal, and located at a much lower elevation of below −4250 m. Kieserite superposes polyhydrated sulfate-rich deposits, and iron oxides form lags.The facies of sulfate formation remains unclear, and could be different for the two locations. A formation in a lake, playa or under a glacier is consistent with the mineralogy of the central valley and its flat, low-lying topography. This is not conceivable for the kieserite deposits observed south of Ophir Mensa. These deposits are observed over several thousands of meters of elevation, which would require a standing body of water several thousands of meters deep. This would have lead to much more pervasive sulfate deposits than observed. These deposits are therefore more consistent with evaporation of groundwater infiltrating into previously sulfate-free light-toned deposits. The overlying polyhydrated sulfates and other mineral phases are observed in outcrops on ridges along the slopes of the southern chasm wall, which are too exposed to be reached by groundwater. Here, a water supply from the atmosphere by rain, snow, fog or frost is more conceivable.  相似文献   

Carbon dioxide on the satellites of Saturn: Results from the Cassini VIMS investigation and revisions to the VIMS wavelength scale     

Dale P. Cruikshank  Allan W. Meyer  Roger N. Clark  Katrin Stephan  Scott A. Sandford  Gianrico Filacchione  Philip D. Nicholson  Thomas B. McCord  J. Brad Dalton  Dennis L. Matson 《Icarus》2010,206(2):561-572

Several of the icy satellites of Saturn show the spectroscopic signature of the asymmetric stretching mode of C-O in carbon dioxide (CO₂) at or near the nominal solid-phase laboratory wavelength of 4.2675 μm (2343.3 cm⁻¹), discovered with the Visible-Infrared Mapping Spectrometer (VIMS) on the Cassini spacecraft. We report here on an analysis of the variation in wavelength and width of the CO₂ absorption band in the spectra of Phoebe, Iapetus, Hyperion, and Dione. Comparisons are made to laboratory spectra of pure CO₂, CO₂ clathrates, ternary mixtures of CO₂ with other volatiles, implanted and adsorbed CO₂ in non-volatile materials, and ab initio theoretical calculations of CO₂ * nH₂O. At the wavelength resolution of VIMS, the CO₂ on Phoebe is indistinguishable from pure CO₂ ice (each molecule’s nearby neighbors are also CO₂) or type II clathrate of CO₂ in H₂O. In contrast, the CO₂ band on Iapetus, Hyperion, and Dione is shifted to shorter wavelengths (typically ∼4.255 μm (∼2350.2 cm⁻¹)) and broadened. These wavelengths are characteristic of complexes of CO₂ with different near-neighbor molecules that are encountered in other volatile mixtures such as with H₂O and CH₃OH, and non-volatile host materials like silicates, some clays, and zeolites. We suggest that Phoebe’s CO₂ is native to the body as part of the initial inventory of condensates and now exposed on the surface, while CO₂ on the other three satellites results at least in part from particle or UV irradiation of native H₂O plus a source of C, implantation or accretion from external sources, or redistribution of native CO₂ from the interior.The analysis presented here depends on an accurate VIMS wavelength scale. In preparation for this work, the baseline wavelength calibration for the Cassini VIMS was found to be distorted around 4.3 μm, apparently as a consequence of telluric CO₂ gas absorption in the pre-launch calibration. The effect can be reproduced by convolving a sequence of model detector response profiles with a deep atmospheric CO₂ absorption profile, producing distorted detector profile shapes and shifted central positions. In a laboratory blackbody spectrum used for radiance calibration, close examination of the CO₂ absorption profile shows a similar deviation from that expected from a model. These modeled effects appear to be sufficient to explain the distortion in the existing wavelength calibration now in use. A modification to the wavelength calibration for 13 adjacent bands is provided. The affected channels span about 0.2 μm centered on 4.28 μm. The maximum wavelength change is about 10 nm toward longer wavelength. This adjustment has implications for interpretation of some of the spectral features observed in the affected wavelength interval, such as from CO₂, as discussed in this paper.  相似文献   

Distribution and interplay of geologic processes on Titan from Cassini radar data     

R.M.C. Lopes  E.R. Stofan  J. Radebaugh  G. Mitri  R.L. Kirk  J.I. Lunine  R. Lorenz  L. Wye  R.J. Ollerenshaw  A. LeGall  R. West  P. Callahan  P. Valora  the Cassini RADAR Team 《Icarus》2010,205(2):540-558

The Cassini Titan Radar Mapper is providing an unprecedented view of Titan’s surface geology. Here we use Synthetic Aperture Radar (SAR) image swaths (Ta-T30) obtained from October 2004 to December 2007 to infer the geologic processes that have shaped Titan’s surface. These SAR swaths cover about 20% of the surface, at a spatial resolution ranging from ∼350 m to ∼2 km. The SAR data are distributed over a wide latitudinal and longitudinal range, enabling some conclusions to be drawn about the global distribution of processes. They reveal a geologically complex surface that has been modified by all the major geologic processes seen on Earth - volcanism, tectonism, impact cratering, and erosion and deposition by fluvial and aeolian activity. In this paper, we map geomorphological units from SAR data and analyze their areal distribution and relative ages of modification in order to infer the geologic evolution of Titan’s surface. We find that dunes and hummocky and mountainous terrains are more widespread than lakes, putative cryovolcanic features, mottled plains, and craters and crateriform structures that may be due to impact. Undifferentiated plains are the largest areal unit; their origin is uncertain. In terms of latitudinal distribution, dunes and hummocky and mountainous terrains are located mostly at low latitudes (less than 30°), with no dunes being present above 60°. Channels formed by fluvial activity are present at all latitudes, but lakes are at high latitudes only. Crateriform structures that may have been formed by impact appear to be uniformly distributed with latitude, but the well-preserved impact craters are all located at low latitudes, possibly indicating that more resurfacing has occurred at higher latitudes. Cryovolcanic features are not ubiquitous, and are mostly located between 30° and 60° north. We examine temporal relationships between units wherever possible, and conclude that aeolian and fluvial/pluvial/lacustrine processes are the most recent, while tectonic processes that led to the formation of mountains and Xanadu are likely the most ancient.  相似文献