Test of the vibrational modelling for the λ-type transitions: Application to the α-β quartz transition

Vibrational modelling is at the present time the only known way to predict the heat capacities of the Earth's mantle minerals at high-pressure and high-temperature. To test the validity of this method for λ-type transitions, we have applied it to the α-β quartz transition (T ₀=846±1 K). Raman spectra of quartz were recorded up to 900 K. Measured frequency shifts of the α-quartz Raman modes were then used in conjunction with available high-pressure Raman data to calculate intrinsic mode anharmonicity, through the parameter a _i=(?Lnv_i/?T)_v. Vibrational modelling of the heat capacity at constant volume, Cv, and at constant pressure, Cp, including anharmonic corrections deduced from the a _i parameters, are compared to experimental data. Taking into account the soft-mode associated to the α-β quartz transition, the model reproduces the excess of Cp related to the transition. Then, this study confirms that detecting a soft-mode from vibrational data allows one to predict λ-type transitions. However, when modelling the thermodynamic properties, the contribution of a soft-mode cannot be established from spectroscopic data. Therefore, one needs first to determine this contribution in order to predict the heat capacities of Earth's mantle minerals displaying λ-type transitions. In α-quartz, this contribution has been determined as 0.007% of the total number of the optic modes in the model of the density of states.     

Offshore Absolute Calibration of Space-Borne Radar Altimeters

Absolute calibration of sea level measurements collected from space-borne radar altimeters is usually performed with respect to collocated sea level in situ records from tide gauges or GPS buoys (Ménard et al. 1994 Ménard, Y., Jeansou, E. and Vincent, P. 1994. Calibration of the TOPEX-Poseidon altimeters at Lampedusa: Additional results at Harves. J. Geophys Res., 99(C12): 24487–24504. http://dx.doi.org/10.1029%2F94JC01300 [Google Scholar]; Haines et al. 1996 Haines, B. J., Christensen, E. J., Norman, R. A., Parke, M. E., Born, G. H. and Gill, S. K. 1996. Altimeter calibration and geophysical monitoring from collocated measurements at the Harvest oil platform. EOS Trans. Suppl., 77(22): W16 [Google Scholar]; Bonnefond et al. 2003; Haines et al. 2003 Haines, B. J., Dong, D., Born, G. H. and Gill, S. K. 2003. The Harvest experiment: Monitoring Jason-1 and TOPEX/Poseidon from a California offshore platform. Mar. Geod., 26: 239–259. [Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]; Schum et al. 2003 Schum, C. K., Yi, Y., Cheng, K., Kuo, C., Braun, A., Calmant, S. and Chambers, D. 2003. Calibration of Jason-1 Altimeter over Lake Erie. Mar. Geod., 26: 335–354.  [Google Scholar]; Watson et al. 2003 Watson, C., Coleman, R., White, N., Church, J. and Govind, R. 2003. Absolute calibration of TOPEX/ Poseidon and Jason-1 using GPS buoys in Bass Strait, Australia. Mar. Geod., 26: 285–304. [Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]; Watson et al. 2004 Watson, C., White, N., Coleman, R., Church, J., Morgan, P. and Govind, R. 2004. TOPEX/Poseidon and Jason-1: Absolute calibration in Bass Strait, Australia. Mar. Geod., 27: 107–131. http://dx.doi.org/10.1080%2F01490410490465373[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]). Such a method allows regular and long-term control of altimetric systems with independent records. However, this approach is based on a single, geographically dependent point. In order to obtain more significant and accurate bias and drift estimates, there is a strong interest in multiplying the number of calibration opportunities. This article describes a method, called the “offshore method” that was developed to extend the single-point approach to a wider regional scale. The principle is to compare altimeter and tide gauge sea level data not only at the point of closest approach of an overflying pass, but also at distant points along adjacent satellite passes. However, connecting sea level satellite measurements with more distant in situ data requires a more accurate determination of the geoid and mean ocean dynamic topography slopes, and also of the ocean dynamical changes. In this demonstration experiment, 10 years of averaged TOPEX/Poseidon mean sea level profiles are used to precisely determine the geoid and the mean ocean circulation slope. The Mog2d barotropic ocean model (Carerre et Lyard 2003 Carrère, L. and Lyard, F. 2003. Modelling the barotropic response of the global ocean to atmospheric wind and pressure forcing-comparisons with observations. GRL, 30(6): 1275 [Google Scholar]) is used to improve our estimate of the ocean dynamics term. The method is first validated with Jason-1 data, off Corsica, where the dedicated calibration site of Senetosa provides independent reference data. The method is then applied to TOPEX/Poseidon on its new orbit and to Geosat Follow On. The results demonstrate that it is feasible to make altimeter calibrations a few tens to hundreds of kilometers away from a dedicated site, as long as accurate mean sea level altimeter profiles can be used to ensure the connection with reference tide gauges.     

A Compilation of Silicon,Rare Earth Element and Twenty‐One other Trace Element Concentrations in the Natural River Water Reference Material SLRS‐5 (NRC‐CNRC)

The natural river water certified reference material SLRS‐5 (NRC‐CNRC) was routinely analysed in this study for major and trace elements by ten French laboratories. Most of the measurements were made using ICP‐MS. Because no certified values are assigned by NRC‐CNRC for silicon and 35 trace element concentrations (rare earth elements, Ag, B, Bi, Cs, Ga, Ge, Li, Nb, P, Rb, Rh, Re, S, Sc, Sn, Th, Ti, Tl, W, Y and Zr), or for isotopic ratios, we provide a compilation of the concentrations and related uncertainties obtained by the participating laboratories. Strontium isotopic ratios are also given.     

Exploitation de la fracturation d’un massif par la karstification : exemple du Causse de l’Hortus (Hérault,France)

Résumé

Le Causse de l’Hortus est un massif particulièrement adapté à l’étude de la fracturation et de ses interdépendances avec la karstification. La réalisation en cours d’une monographie hydrogéologique et spéléologique du massif ainsi que l’existence de plus de 20 km de galeries explorées appartenant aux réseaux actifs, permettent d’apporter des données nouvelles face aux précédentes études réalisées dans ce domaine. La confrontation des directions de fracturation visibles sur les photographies aériennes avec les directions réellement exploitées par les réseaux karstiques sur l’ensemble du Causse a permis de mettre en évidence le rôle des fractures majeures et l’influence du gradient hydraulique sur l’exploitation du spectre de fractures. En fin de compte, la mise en évidence des relations existant entre les failles décrochantes dextres et les émergences temporaires de type « boulidou » permet d’aboutir à des applications concrètes tant sur le plan spéléologique que sur le plan hydrogéologique. L’étude de ces « boulidous » apporte également de nouvelles informations sur la structuration verticale du karst. © Elsevier, Paris     

Long Term Evolution of Solar Meridional Circulation and Phase Synchronization Viewed Through a Symmetrical Kuramoto Model

The solar-cycle oscillations of the toroidal and poloidal components of the solar magnetic field in the northern solar hemisphere have a persistent phase difference of about \(\pi \). We propose a symmetrical Kuramoto model with three coupled oscillators as a simple way to understand this anti-synchronization. We solve an inverse problem and reconstruct natural frequencies of the top and bottom oscillators under the conditions of a constant coupling strength and a non-delayed coupling. These natural frequencies are associated with angular velocities of the meridional flow circulation near the solar surface and in the deep layer of the solar convection zone. A relationship between our reconstructions of the shallow and the deep meridional flow speed during recent Solar Cycles 21?–?23 is in agreement with estimates obtained in helioseismology and flux-transport dynamo modeling. The reconstructed top oscillator speed presents significant solar-cycle like variations that agree with recent helioseismical reconstructions. The evolution of reconstructed natural frequencies strongly depends on the coupling strength. We find two stable regimes in the case of strong coupling with a change of regime during anomalous solar cycles. We see the onset of a new transition in Solar Cycle 24. We estimate the admitted range of coupling values and find evidence of cross-equatorial coupling between solar hemispheres not accounted for by the model.     

La vallée d'Ys : un paléoréseau hydrographique immergé en baie de Douarnenez (Finistère,France)

Interpretation of the recent high-resolution survey, CANADOU 2000, in the Bay of Douarnenez (Finistère, France) allowed us to restore the morphology of the substratum and the sedimentary filling of the bay. The Brioverian and Palaeozoic substratum reveals a well-defined network of incised valleys as results of successive emergence stages of the Bay during the Quaternary. Valleys join in a westward-widened mean valley, called Ys Valley. The present-day sedimentary fill of the bay of Douarnenez appears mainly controlled by the Holocene rise and the consecutive highstand. It comprises fluvial and estuarine deposits filling up incised valleys and marine sedimentation extending out of the incised valleys. To cite this article: G. Jouet et al., C. R. Geoscience 335 (2003).To cite this article: G. Jouet et al., C. R. Geoscience 335 (2003).     

La pénétration de l'air froid dans une vallée alpine

Résumé Les observations de deux stations situées à l'entrée de la vallée du Rhône et à l'intérieur de celle-ci permettent de déterminer dans une certaine mesure comment l'air froid pénètre dans cette longue vallée des Alpes suisses. L'accès se fait beaucoup plus souvent par-dessus les montagnes de l'Ouest ou du Nord que par le chenal de la vallée seulement.

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Summary The observations of two stations at the entrance and in the interior of the Rhône valley allow to a certain degree to determine how cold air penetrates this long extended valley of the Swiss Alps. The influx of air takes much more frequently place over the mountains in the West and North than through the trough of the valley.

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Zusammenfassung Die Beobachtungen von zwei Stationen, die am Eingang und im Inneren des Rhonetals gelegen sind, erlauben einigermaßen festzustellen, wie die Kaltluft in dieses langgestreckte Tal der Schweizeralpen eindringt. Dabei erfolgt der Luftzustrom viel häufiger über die Berge im W und N als ausschließlich durch die Talrinne.

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Avec 1 Figure     

Slow and Fast Rotating Coronal Holes from Geomagnetic Indices

The evolution of the 27-day recurrence in the series of two solar indices (Wolf number WN and 10.7 cm radio flux F) and two geomagnetic indices (Dst and ζ, variance of the geomagnetic field recorded at a magnetic observatory) have been studied over the 1957 – 2007 time span. Spectral energies contained in two period domains (25 – 27.3 and 27.3 – 31 days), designated as E ₁ and E ₂, have been computed. Whereas the evolution of E ₁ is the same for the four indices, that of E ₂ is essentially different for WN and F on the one hand, Dst and ζ on the other hand. Some general conclusions on the dynamics of the solar outer layers are inferred from these results. First the solar activity, as measured by WN, and when averaged over a few years, evolves in the same way whatever the latitude. Second, two families of coronal holes (CHs) are identified; the rapidly and the slowly rotating CHs evolve quite differently.