New insight on the genus Nolaniceras Casey, 1961 (Ammonoidea,Cretaceous) and its consequences on the biostratigraphy of the Aptian Stage     

Luc G. Bulot  Jean-Louis Latil  Alex Hairabian  Arnaud Fournillon 《Proceedings of the Geologists' Association. Geologists' Association》2014

Nolaniceras nolani ( Seunes, 1887) has been widely quoted in the Upper Aptian literature over the years. Re-examination of the holotype of the species shows that it has always been misidentified and that this taxon is represented by a single specimen, the holotype, of uncertain age. As a consequence, its use as an index species for the Upper Aptian should be reconsidered and abandoned.  相似文献   

Evidence for delayed poleward expansion of North Atlantic surface waters during the last interglacial (MIS 5e)     

Nicolas Van Nieuwenhove  Henning A. Bauch  Frédérique Eynaud  Evguenia Kandiano  Elsa Cortijo  Jean-Louis Turon 《Quaternary Science Reviews》2011,30(7-8):934-946

The Last Interglacial (Marine Isotopic Stage or MIS 5e) surface ocean heat flux from the Rockall Basin (NE Atlantic) towards the Arctic Ocean was reconstructed by analysing dinoflagellate cyst (dinocyst) assemblages in four sediment cores. Together with records of stable isotopes and ice-rafted detritus, the assemblage data reflect the northward retreat of ice(berg)-laden waters and the gradual development towards interglacial conditions at the transition from the Saalian deglaciation (Termination II) into MIS 5e. At the Rockall Basin, this onset of the Last Interglacial is soon followed by the appearance of the thermophilic dinocyst species Spiniferites mirabilis, with relative abundances higher than those observed at present in the area. North of the Iceland-Scotland Ridge, however, S. mirabilis only appears in significant numbers during late MIS 5e, between ～118 and 116.5 ka. Hence, fully marine Last Interglacial conditions with most intense Atlantic surface water influence occurred during late MIS 5e in the Nordic seas, and consequently also farther north in the Arctic Ocean, and at times when northern hemisphere summer insolation was already significantly decreased. The stratigraphic position of this Late Interglacial optimum is supported by planktic foraminifers and contrasts with the timing of the early Holocene climatic optimum in this area. We interpret the delayed northward expansion of Atlantic waters towards the polar latitudes as a result of the Saalian ice sheet deglaciation and its specific impact on the subsequent water mass evolution in this region.  相似文献   

Identification of Gleissberg Cycles and a Rising Trend in a 315-Year-Long Series of Sunspot Numbers     

Jean-Louis Le Mouël  Fernand Lopes  Vincent Courtillot 《Solar physics》2017,292(3):43

We show in this short note that the method of singular spectrum analysis (SSA) is able to clearly extract a strong, clean, and clear component from the longest available sunspot (International Sunspot Number, ISN) time series (1700?–?2015) that cannot be an artifact of the method and that can be safely identified as the Gleissberg cycle. This is not a small component, as it accounts for 13% of the total variance of the total original signal. Almost three and a half clear Gleissberg cycles are identified in the sunspot number series. Four extended solar minima (XSM) are determined by SSA, the latest around 2000 (Cycle 23/24 minimum). Several authors have argued in favor of a double-peaked structure for the Gleissberg cycle, with one peak between 55 and 59 years and another between 88 and 97 years. We find no evidence of the former: solar activity contains an important component that has undergone clear oscillations of \(\approx90\) years over the past three centuries, with some small but systematic longer-term evolution of “instantaneous” period and amplitude. Half of the variance of solar activity on these time scales can be satisfactorily reproduced as the sum of a monotonous multi-secular increase, a \(\approx90\)-year Gleissberg cycle, and a double-peaked (\(\approx10.0\) and 11.0 years) Schwabe cycle (the sum amounts to 46% of the total variance of the signal). The Gleissberg-cycle component definitely needs to be addressed when attempting to build dynamo models of solar activity. The first SSA component offers evidence of an increasing long-term trend in sunspot numbers, which is compatible with the existence of the modern grand maximum.  相似文献   

High resolution simulation of the South Asian monsoon using a variable resolution global climate model   总被引：2，自引：1，他引：1  

T. P Sabin  R. Krishnan  Josefine Ghattas  Sebastien Denvil  Jean-Louis Dufresne  Frederic Hourdin  Terray Pascal 《Climate Dynamics》2013,41(1):173-194

This study examines the feasibility of using a variable resolution global general circulation model (GCM), with telescopic zooming and enhanced resolution (~35 km) over South Asia, to better understand regional aspects of the South Asian monsoon rainfall distribution and the interactions between monsoon circulation and precipitation. For this purpose, two sets of ten member realizations are produced with and without zooming using the LMDZ (Laboratoire Meteorologie Dynamique and Z stands for zoom) GCM. The simulations without zoom correspond to a uniform 1° × 1° grid with the same total number of grid points as in the zoom version. So the grid of the zoomed simulations is finer inside the region of interest but coarser outside. The use of these finer and coarser resolution ensemble members allows us to examine the impact of resolution on the overall quality of the simulated regional monsoon fields. It is found that the monsoon simulation with high-resolution zooming greatly improves the representation of the southwesterly monsoon flow and the heavy precipitation along the narrow orography of the Western Ghats, the northeastern mountain slopes and northern Bay of Bengal (BOB). A realistic Monsoon Trough (MT) is also noticed in the zoomed simulation, together with remarkable improvements in representing the associated precipitation and circulation features, as well as the large-scale organization of meso-scale convective systems over the MT region. Additionally, a more reasonable simulation of the monsoon synoptic disturbances (lows and disturbances) along the MT is noted in the high-resolution zoomed simulation. On the other hand, the no-zoom version has limitations in capturing the depressions and their movement, so that the MT zone is relatively dry in this case. Overall, the results from this work demonstrate the usefulness of the high-resolution variable resolution LMDZ model in realistically capturing the interactions among the monsoon large-scale dynamics, the synoptic systems and the meso-scale convective systems, which are essential elements of the South Asian monsoon system.  相似文献   

The respective roles of surface temperature driven feedbacks and tropospheric adjustment to CO2 in CMIP5 transient climate simulations     

Lorenzo Tomassini  Olivier Geoffroy  Jean-Louis Dufresne  Abderrahmane Idelkadi  Chiara Cagnazzo  Karoline Block  Thorsten Mauritsen  Marco Giorgetta  Johannes Quaas 《Climate Dynamics》2013,41(11-12):3103-3126

An overview of radiative climate feedbacks and ocean heat uptake efficiency diagnosed from idealized transient climate change experiments of 14 CMIP5 models is presented. Feedbacks explain about two times more variance in transient climate response across the models than ocean heat uptake efficiency. Cloud feedbacks can clearly be identified as the main source of inter-model spread. Models with strong longwave feedbacks in the tropics feature substantial increases in cloud ice around the tropopause suggestive of changes in cloud-top heights. The lifting of the tropical tropopause goes together with a general weakening of the tropical circulation. Distinctive inter-model differences in cloud shortwave feedbacks occur in the subtropics including the equatorward flanks of the storm-tracks. Related cloud fraction changes are not confined to low clouds but comprise middle level clouds as well. A reduction in relative humidity through the lower and mid troposphere can be identified as being the main associated large-scale feature. Experiments with prescribed sea surface temperatures are analyzed in order to investigate whether the diagnosed feedbacks from the transient climate simulations contain a tropospheric adjustment component that is not conveyed through the surface temperature response. The strengths of the climate feedbacks computed from atmosphere-only experiments with prescribed increases in sea surface temperatures, but fixed CO₂ concentrations, are close to the ones derived from the transient experiment. Only the cloud shortwave feedback exhibits discernible differences which, however, can not unequivocally be attributed to tropospheric adjustment to CO₂. Although for some models a tropospheric adjustment component is present in the global mean shortwave cloud feedback, an analysis of spatial patterns does not lend support to the view that cloud feedbacks are dominated by their tropospheric adjustment part. Nevertheless, there is positive correlation between the strength of tropospheric adjustment processes and cloud feedbacks across different climate models.  相似文献   

Kuramoto Model of Nonlinear Coupled Oscillators as a Way for Understanding Phase Synchronization: Application to Solar and Geomagnetic Indices     

Elena M. Blanter  Jean-Louis Le Mouël  Mikhail G. Shnirman  Vincent Courtillot 《Solar physics》2014,289(11):4309-4333

We apply a Kuramoto model of nonlinear coupled oscillators to the simulation of slow variations of the phase difference between sunspot number [R _I ] and geomagnetic indices [aa and ζ]. The Kuramoto model is described for the particular case of two oscillators connected by symmetric coupling with quasi-stationary behavior, and its properties are investigated. By solving an inverse problem, we reconstruct the evolution of the couplings between pairs of indices [R _I and aa, R _I and ζ, aa and ζ], and interpret these in terms of the physics of the solar dynamo. The de-correlation between R _I and geomagnetic indices found in Solar Cycle 20 by Le Mouël et al. (J. Geophys. Res. 117, A09103, 2012) is successfully reproduced by the Kuramoto model and corresponds to the alternation of the leading oscillator. Application of the Kuramoto model to the cross-correlations [C(R _I ,ζ) and C(aa,ζ)] for ζ-indices computed in eight geomagnetic stations shows the latitudinal dependence of the mean phase difference. We discuss these results in terms of the solar-wind contribution to local geomagnetic indices [ζ].  相似文献   

The late 1960s secular variation impulse, the eleven year magnetic variation and the electrical conductivity of the deep mantle   总被引：2，自引：0，他引：2  

Joël Ducruix  Vincent Courtillot  Jean-Louis Le  Mouël 《Geophysical Journal International》1980,61(1):73-94

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Western extension of the Iberian-European plate boundary during the Early Cenozoic (Pyrenean) convergence: A new model — Reply     

S. Grimaud  G. Boillot  B.J. Collette  A. Mauffret  P.R. Miles  D.B. Roberts 《Marine Geology》1983,53(3):238-239

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Diagenesis of the Aphebian Mistassini regolith,Quebec, Canada     

E.H. Chown  Jean-Louis Caty 《Precambrian Research》1983,19(3):285-299

A well-developed regolith is preserved beneath early Proterozoic (Aphebian) rocks of the Otish and Mistassini Groups in Central Quebec, Canada. The regolith is covered by fluviatile clastic rocks (Otish Group) in the north, and by a thick sequence of stromatolitic and sandy dolomite (Mistassini Group) in the south.Where preserved beneath clastic rocks, the regolith exhibits the structures and textures of its crystalline parent rocks (tonalite, gneiss and amphibolite), despite the alteration of feldspars to clay minerals and the partial oxidation of biotite. A later event recrystallized the clay minerals to muscovite, while conserving the original outline of the feldspars. Beneath the dolomite, the regolith was largely replaced by dolomite, but retains many original textures. Dolomite replaced first the clay minerals, then quartz and unaltered feldspars and finally biotite. Repeated crustifications of dolomite with intervals of chert and minor anthraxolite surround unaltered blocks of crystalline rock within the regolith profile and similar complex veins fill many master joints. These veins are identical in composition to vug fillings throughout the overlying carbonate formations. Clasts of partly dolomitized regolith included in non-dolomitic sands filling channels and scours dug deep into the profile, suggest that dolomitization commenced very early, possibly related to a sabkha environment developed during the transgression.  相似文献   

Planetary theories with the aid of the expansions of elliptic functions     

Jean Chapront  Jean-Louis Simon 《Celestial Mechanics and Dynamical Astronomy》1995,63(2):171-188

For coplanar circular orbits, the mutual perturbations between two bodies can be expressed in term of the argument of Jacobian elliptic functions instead of the difference of the mean longitudes. For a given pair of planets, such a change of time variable improves the convergence of the developments. At the first order of planetary masses an integration of Lagrange's equations for the osculating elements is performed. When compared to classical developments the results are reduced by an important factor. The method is then extended to the mutual perturbations of Jupiter and Saturn, at any order of planetary masses, either with Fourier series with two arguments, or with one argument solely, taking advantage of the close commensurability of the mean motions.  相似文献