Variability of precipitation intensity: sensitivity to treatment of moist convection in an RCM and a GCM

The present study investigates the sensitivity of the frequency distribution of precipitation rates to the closure employed in the penetrative mass flux cumulus parameterization of Zhang and McFarlane in the Canadian regional climate model (CRCM) and in the Canadian Centre for Climate Modelling and Analysis third generation global atmospheric general circulation model (AGCM3). The effects of an alternative prognostic closure for mass flux cumulus parameterization in place of the original diagnostic closure are investigated. A set of experiments is performed in which changes in the frequency distribution of precipitation rates and cloud base mass-flux are examined as a function of the parameters that define each closure scheme. The relationship between the frequency distribution of precipitation and cloud base mass flux is examined and a self-consistent relation is found when the depth of convection is taken into account. Experiments performed with the prognostic closure favor relatively strong cloud base mass-flux and deep penetrative convection with relatively more intense convective precipitation. The mean of the frequency distribution of convective precipitation is larger and the heavier events become more intense. Also, experiments performed with the prognostic closure favor less frequent convective activity. However these changes in the distribution of convective component of precipitation are generally offset by opposite changes in the distribution of the resolved large-scale component of precipitation, resulting in relatively smaller changes in total precipitation. The altered partition of precipitation between convective and large-scale components is found to alter the energy balance and the thermodynamic equilibrium structure of the troposphere. The robustness found in the CRCM results regarding the sensitivity of the frequency distribution of precipitation to changes in the closure of the deep convection parameterization is investigated by performing a similar analysis of AGCM3 simulations. A remarkable similarity of AGCM3 and CRCM results is found suggesting that the closure sensitivity identified in this study is robust.     

Enrichment of redox-sensitive trace metals (U,V, Mo,As) associated with the late Hauterivian Faraoni oceanic anoxic event

The Faraoni Level is a short-lived oxygen-deficient event that took place during the latest Hauterivian. In order to improve our understanding of the palaeoenvironmental conditions that occurred during this event, we have analysed the contents of several redox-sensitive trace elements (U, V, Mo, As, Co, Cd, Cu, Zn, Ni, Pb, Cr) from bulk limestone samples of late Hauterivian–early Barremian age from three reference sections. U, V, Mo and As show consistent and significant enrichments during the Faraoni event whereas the other redox-sensitive trace elements analysed here are not systematically enriched. In order to explain this discrepant behaviour, we propose that the Faraoni Level was deposited during a period of anoxic conditions near the sediment–water interface. The distinctive peaks in U, V, Mo and As contents are traceable throughout the three studied sections and represent a good correlation tool which helps to identify the Faraoni Level and its equivalents in the western Tethyan realm and outside of the Tethys. For example, a peak in U contents in upper Hauterivian sediments of the northwestern Pacific realm (ODP leg 185, site 1149) may well be an expression of the Faraoni event in this particular basin.     

Carlin-type gold mineralization at Saint-André-de-Ristigouche,Gaspé Peninsula (Québec), Canadian Appalachians

The Gaspé Peninsula, in the Canadian Appalachians, hosts a variety of mineral occurrences that are spatially associated with the Grand Pabos and Restigouche faults. Among these occurrences, the Saint-André-de-Ristigouche gold (SAR-Au) showing has peculiar features comparable with Carlin-type gold deposits at the regional, district, and prospect scales. The most striking ones are: (1) the calcareous nature of the host rocks; (2) the Au-As-Sb-Hg metallic signature with absence of base metals and Ag; (3) the association with a crustal scale fault zone; (4) the hydrothermal alteration characterized by silicification, calcite, and quartz veinlets at the margin of the Au-bearing zones and the occurrence of kaolinite in large halos of argillic alteration; (5) numerous felsic dikes; (6) the occurrence of Au in As-rich pyrite forming overgrowths on premineralization As-free pyrite, and in arsenopyrite; (7) hydrothermal fluids equilibrated with host rocks at high temperature (>200°), which cooled to precipitate arsenopyrite and then mixed with evolved meteoric water to precipitate stibnite in veins. Although the SAR-Au showing is relatively small, analogies with Carlin-type mineralization encourage exploration in the Gaspé Peninsula and in similar settings elsewhere in the Appalachians.     

L'aspidolite fluorée : rôle des évaporites dans la genèse du rubis des marbres de Nangimali (Azad-Kashmir,Pakistan)

Ruby-bearing marbles from Nangimali, in the Azad-Kashmir, Pakistan, contain, besides phengite, different mica intergrowths: paragonite, phlogopite and aspidolite (sodium phlogopite). Both phlogopites, intimately linked and coexisting with paragonite, are fluorine rich, contrary to phengite and paragonite. F-enriched aspidolite is described for the first time. Phengite is either associated with phlogopite or could be isolated. The presence of aspidolite in the ruby-bearing marbles, together with other arguments such as salt solid inclusions and presence of anhydrite, suggest the implication of evaporites in the genesis of gem corundums. To cite this article: V. Garnier et al., C. R. Geoscience 336 (2004).     

Airborne microphysical measurements and radar reflectivity observations near a cold frontal rainband observed during the FRONTS 87 experiment

Airborne microphysical measurements and ground-based radar-reflectivity observations, collected at the near of a narrow cold frontal rainband during the FRONTS 87 experiment, are used to infer some characteristics of the precipitation: size-distribution, liquid or ice-water content, mass-weighted fallspeed, radar-reflectivity and relationships between pairs of these quantities. In the ice phase region, two different methods are proposed to calculate the radar reflectivity from the aircraft data. The influence of the choice of the ice particle type on the calculated quantities is discussed from the results of the first method. The second method is new: it is based upon the use of a roughness parameter estimated from the analysis of the two-dimensional particle images of ice precipitation. Although this method is tentative, it gives conclusive results for the two different flight levels studied here.     

Direct calibration of the Cepheid period–luminosity relation

After the first release of Hipparcos data, Feast & Catchpole gave a new value for the zero-point of the visual Cepheid period–luminosity relation, based on trigonometric parallaxes. Because of the large uncertainties on these parallaxes, the way in which individual measurements are weighted is of crucial importance. We therefore conclude that the choice of the best weighting system can be aided by a Monte Carlo simulation. On the basis of such a simulation, it is shown that (i) a cut ‐off in π or in σ _π π introduces a strong bias; (ii) the zero-point is more stable when only the brightest Cepheids are used; and (iii) the Feast & Catchpole weighting gives the best zero-point and the lowest dispersion. After correction, the adopted visual period–luminosity relation is 〈 M _V 〉=−2.77 log  P −1.44±0.05. Moreover, we extend this study to the photometric I band (Cousins) and obtain 〈 M _I 〉=−3.05 log  P −1.81±0.09.     

Extragalactic Cepheid database

We present in this paper an exhaustive compilation of all published data of extragalactic Cepheids. We have checked every light curve in order to characterize the different types of Cepheid and detect potential overtone pulsators, or to estimate the quality of the data. This compilation of about 3000 photometric measurements will constitute a very useful tool for astronomers involved for instance in the extragalactic distance scale.     

The European level in EU governance: territory, authority and trans-scalar networks

This article offers an analysis of the emerging scalar configuration of the governance of the European Union. It discusses how European integration stands for a move from a collection of territorially homogenous systems of rule towards a new assemblage of territories, authorities and rights. The paper first questions the stretchy territoriality of the seemingly obvious European level. Second it analyses the sectoral differences in the evolution of the width and the depth of integration, measured as the transfer of competencies to the EU level between the Rome Treaty (1958) and the Lisbon Treaty (200y). Third it turns to the day-to-day decision-making to assess the relations between players in EU governance and finally it looks more closely at the administrative wheels of the EU machinery.