Meridional distribution of CH3C2H and C4H2 in Saturn’s stratosphere from CIRS/Cassini limb and nadir observations

Limb and nadir spectra acquired by Cassini/CIRS (Composite InfraRed Spectrometer) are analyzed in order to derive, for the first time, the meridional variations of diacetylene (C₄H₂) and methylacetylene (CH₃C₂H) mixing ratios in Saturn’s stratosphere, from 5 hPa up to 0.05 hPa and 80°S to 45°N. We find that the C₄H₂ and CH₃C₂H meridional distributions mimic that of acetylene (C₂H₂), exhibiting small-scale variations that are not present in photochemical model predictions. The most striking feature of the meridional distribution of both molecules is an asymmetry between mid-southern and mid-northern latitudes. The mid-southern latitudes are found depleted in hydrocarbons relative to their northern counterparts. In contrast, photochemical models predict similar abundances at north and south mid-latitudes. We favor a dynamical explanation for this asymmetry, with upwelling in the south and downwelling in the north, the latter coinciding with the region undergoing ring shadowing. The depletion in hydrocarbons at mid-southern latitudes could also result from chemical reactions with oxygen-bearing molecules.Poleward of 60°S, at 0.1 and 0.05 hPa, we find that the CH₃C₂H and C₄H₂ abundances increase dramatically. This behavior is in sharp contradiction with photochemical model predictions, which exhibit a strong decrease towards the south pole. Several processes could explain our observations, such as subsidence, a large vertical eddy diffusion coefficient at high altitudes, auroral chemistry that enhances CH₃C₂H and C₄H₂ production, or shielding from photolysis by aerosols or molecules produced from auroral chemistry. However, problems remain with all these hypotheses, including the lack of similar behavior at lower altitudes.Our derived mean mixing ratios at 0.5 hPa of (2.4 ± 0.3) × 10⁻¹⁰ for C₄H₂ and of (1.1 ± 0.3) × 10⁻⁹ for CH₃C₂H are compatible with the analysis of global-average ISO observations performed by Moses et al. (Moses, J.I., Bézard, B., Lellouch, E., Gladstone, G.R., Feuchtgruber, H., Allen, M. [2000a]. Icarus 143, 244-298). Finally, we provide values for the ratios [CH₃C₂H]/[C₂H₂] and [C₄H₂]/[C₂H₂] that can constrain the coupled chemistry of these hydrocarbons.     

Stochastic simulations of fault networks in 3D structural modeling

3D structural modeling is a major instrument in geosciences, e.g. for the assessment of groundwater and energy resources or nuclear waste underground storage. Fault network modeling is a particularly crucial step during this task, for faults compartmentalize rock units and plays a key role in subsurface flow, whether faults are sealing barriers or drains. Whereas most structural uncertainty modeling techniques only allow for geometrical changes and keep the topology fixed, we propose a new method for creating realistic stochastic fault networks with different topologies. The idea is to combine an implicit representation of geological surfaces which provides new perspectives for handling topological changes with a stochastic binary tree to represent the spatial regions. Each node of the tree is a fault, separating the space in two fault blocks. Changes in this binary tree modify the fault relations and therefore the topology of the model.     

Determinants of corporate adaptation to climate change in winter tourism: An econometric analysis

While corporate adaptation strategies in response to climate change have been characterized, the determinants of adaptation have not been comprehensively analyzed. Knowledge of these determinants is particularly useful for policy makers to provide favorable conditions in support of corporate adaptation measures. Based on unique data from a survey of Swiss ski lift operators, this paper empirically examines such determinants at the business level. Our econometric analysis with linear regression and count data models finds a positive influence of the awareness of possible climate change effects on the scope of corporate adaptation. Surprisingly, no significant influence of the vulnerability to climate change effects on the scope of adaptation could be found. Finally, the dependency on the affected business and the ability to adapt influence the specific strategic directions of corporate adaptation.     

Sikhote Alin' meteoroid: A contribution to the story of its fragmentation and fragment scattering

The correlation of the size and spatial distribution of fragments from the Sikhote Alin' meteoroid, 1947, was examined.With Frost's logarithmic rule of spatial sorting of meteorite fragments, supported by an ad hoc developed averaging procedure, a new approach to the size distribution was made possible.It was found that the meteoroid has been originally broken into several - presumably 5–6 - large fragments unequal in size, which further fragmented with various efficiency and speed.The conclusions are compatible with the reports of the witnesses of the fall of the meteorite.     

Pressure-induced structural modifications in Mg2GeO4-olivine: A Raman spectroscopic study

Raman spectra of Mg₂GeO₄-olivine were obtained from ambient pressure up to 34 GPa at ambient temperature. Under quasi-hydrostatic pressure conditions, the following modifications in the Raman spectra occur as pressure increases: 1) near 11 GPa, two sharp extra bands appear in the 600–700 cm^?1 frequency range, and increase in intensity with respect to the olivine bands; 2) above 22 GPa, these two bands become very intense, and the number, position and relative intensity of the other vibrational bands drastically change; 3) the intensity of sharp bands progressively decreases above 25 GPa. The transformation occurs at lower pressures under non-hydrostatic conditions. During decompression to atmospheric pressure, the high-pressure phase partially reverts to olivine. These observations can be interpreted as the progressive metastable transformation from the olivine structure to a crystalline phase with four-fold coordinated Ge, in which the GeO₄ tetrahedra are polymerized. We propose that the metastable high-pressure phase is a structurally disordered spinelloid close to the hypothethical ω- or ?^*-phase, and forms by a shear mechanism assisted by the development of a dynamical instability in the olivine structure. Implications for the transformations undergone by olivines under far-from-equilibrium conditions (e.g. in subducting lithospheric slabs and in shocks) are discussed.     

Selected solar wind parameters at 1 AU through two solar activity cycles

In situ measurements of the solar wind largely cover more than two solar magnetic activity cycles, namely 20 and 21. This is a very appealing opportunity to study the influence of the activity cycle on the behaviour of the solar wind parameters. As a matter of fact, many authors so far have studied this topic comparing the long-term magnetic field and plasma averages. However, when the average values are evaluated on a data sample whose duration is comparable with (or even longer than) the solar rotation period we lose information about the contribution due to the fast and the slow solar wind components. Thus, discriminating in velocity plays a key role in understanding solar cycle effects on the solar wind. Based on these considerations, we performed a separate analysis for fast and slow wind, respectively. In particular, we found that: (a) fast wind carries a slightly larger momentum flux density at 1 AU, probably due to dynamic stream-stream interaction; (b) proton number density in slow wind is more cycle dependent than in fast wind and decreases remarkably across solar maximum; (c) fast wind generally carries a magnetic field intensity stronger than that carried by the slow wind; (d) we found no evidence for a positive correlation between velocity and field intensity as predicted by some theories of solar wind acceleration; (e) our results would support an approximately constant divergence of field lines associated with corotating high-velocity streams.     

Lead isotope study of basic-ultrabasic layered complexes: Speculations about the age of the earth and primitive mantle characteristics

In order to explore mantle heterogeneity through geological time, Pb isotopic compositions have been determined for 8 differentiated-layered intrusions whose ages are between 2.7 and 0.05 b.y.. The Pb-Pb ages of these intrusions and the U-Pb characteristics of their parent sources are discussed.The Pb-Pb dating method is found to be applicable for this type of basic or ultrabasic rocks and agrees satisfactorily with other available methods. Significant differences are found between the calculated values for the parent bodies of these intrusions. This could reflect either mantle heterogeneity since Archean times, or contamination of some of the bodies by continental crust. Discrimination between these hypotheses can be proposed from the positions of the initial Sr ratios of these massives in respect to the supposed “terrestrial” evolution line. The two intrusions which plot on that closed system Sr evolution line (Muntsche Tundra, U.S.S.R., and Skaergaard, Greenland) belong also to a simple two-stage evolution model for Pb, with a low first-stage μ value of 7.8. If these two bodies are considered as pieces of a “primitive” closed-system mantle, a4.55 ± 0.01 age of the earth can be calculated from their Pb initial ratios.     

X-ray determination and equilibrium composition of clinopyroxenes in the system CaO-MgO-Al2O3-SiO2

Ternary clinopyroxenes have been synthesized in the plane Di-CaTs-En. The variation of their crystallographic parameters has allowed the development of three determinative grids, which utilize b-, 2 _22¯1–2 ₃₁₀ and 2 ₃₃₀ –2 ₂₀₂ respectively. These grids show significant differences in comparison with the previously proposed ones. Present results have been used to review some data on clinopyroxenes equilibria in the system CaO-MgO-Al₂O₃-SiO₂ (CMAS) (Biggar 1969; Bruno and Facchinelli 1978; Herzberg 1978; O'Hara and Schairer 1963; Boyd 1969). In particular the petrogenic grid correlating P, T and CaTs content of clinopyroxenes in spinel-lherzolite assemblage (Herzberg 1978) has been revised, and consequently equilibrium temperatures rise by one hundred degrees.     

Discovery of the largest impact crater field on Earth in the Gilf Kebir region, Egypt

Using orbital imaging radar, we have detected a large number of circular structures in the southwestern Egyptian desert, covering more than 4500 km² close to the Gilf Kebir plateau in sandstones of Upper Cretaceous. Fieldwork confirmed that it is a new impact crater field: 13 craters from 20 m to 1 km in diameter were studied. The impact origin is confirmed by the observation of shock-related structures, such as shatter cones and planar fractures in quartz grains of breccia. Considering the extension of the crater field, it was possibly created by several meteorites that broke up when entering the atmosphere. To cite this article: P. Paillou et al., C. R. Geoscience 336 (2004).

Résumé

À partir d'images satellites issues de systèmes radar, nous avons détecté un grand nombre de structures circulaires dans le Sud-Ouest du désert égyptien, s'étendant sur plus de 4500 km² à l'est du plateau du Gilf Kebir, dans des grès du Crétacé supérieur. Une étude sur le terrain a permis de vérifier qu'il s'agit d'un champ d'impacts météoritiques jusque là inconnu : 13 structures, d'un diamètre compris entre 20 m et 1 km, ont été reconnues comme cratères d'impact. La présence d'un grand nombre de cônes de percussion et de brèches dans lesquelles des quartz choqués à structures planaires ont été observés confirment l'hypothèse de l'impact. Considérant l'extension du champ d'impact, il a probablement été créé par plusieurs météorites qui se sont fragmentées dans l'atmosphère terrestre. Pour citer cet article : P. Paillou et al., C. R. Geoscience 336 (2004).