“Proterozoic–Early Paleozoic evolution in western South America—a discussion” in: Tectonophysics, 354: 121–137 (2002)     

Ricardo A. Astini  Augusto E. Rapalini   《Tectonophysics》2003,366(1-2):143-148

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A crystal-chemical investigation of Cr substitution in muscovite by XANES spectroscopy     

A. Cardelli  G. Cibin  M. Benfatto  S. Della Longa  M. F. Brigatti  A. Marcelli 《Physics and Chemistry of Minerals》2003,30(1):54-58

 This work introduces a novel procedure to fit the scattering features of XANES spectra. The procedure was applied and validated on a chromium-containing muscovite for which structural and crystal-chemical characterization is available from literature. The simulation, which involved clusters formed by up to 90 atoms, proved to be effective in representing the Cr local environment, even if the system is characterized by a very low metal content, as demonstrated by the extremely good correspondence with experimental data. Received: 23 May 2002 / Accepted: 6 November 2002  相似文献   

Changing moisture sources over the last 330,000 years in Northern Oman from fluid-inclusion evidence in speleothems     

Dominik Fleitmann  Stephen J BurnsUlrich Neff  Augusto ManginiAlbert Matter 《Quaternary Research》2003,60(2):223-232

Speleothems from Hoti Cave in northern Oman provide a record of continental pluvial periods over the last 330,000 yr. Periods of rapid speleothem deposition occurred from 6000 to 10,500, 78,000 to 82,000, 120,000 to 135,000, 180,000 to 200,000, and 300,000 to 330,000 yr ago, with little or no growth during the intervening periods. During each of these five pluvial periods, δD values of water extracted from speleothem fluid inclusions (δD_FI) are between −60 and −20‰ (VSMOW) and δ¹⁸O values of speleothem calcite (δ¹⁸O_C) are between −12 and −4‰ to (VPDB). These values are much more negative than modern rainfall (for δD) or modern stalagmites (for δ¹⁸O). Previous work on the isotopic composition of rainfall in Oman has shown that northern and southern moisture sources are isotopically distinct. Combined measurements of the δD values of fluid-inclusion water with calculated δ¹⁸O values from peak interglacial speleothems indicate that groundwater was predominantly recharged by the southern (Indian Ocean) moisture source, when the monsoon rainfall belt moved northward and reached Northern Oman during each of these periods.  相似文献   

Quasi-conservative behaviour of Be in deep waters of the Weddell Sea and the Atlantic sector of the Antarctic Circumpolar Current     

M. Frank  M.M. Rutgers van der LoeffPeter W. Kubik  Augusto Mangini 《Earth and Planetary Science Letters》2002,201(1):171-186

We present the first transect of dissolved ¹⁰Be depth profiles across the Antarctic Circumpolar Current (ACC) in the Atlantic sector. North of the Polar Front the ¹⁰Be concentrations increase continuously from very low values at the surface to values of up to 1600 atoms/g at depth. Deep water ¹⁰Be concentrations of particular water masses are consistent with earlier results obtained further north. South of the Polar Front and in the Weddell Sea the distribution of ¹⁰Be is also characterised by low surface concentrations but below 1000 m depth the concentrations are relatively constant and significantly higher (up to 2000 atoms/g) than further north, probably as a result of mixing and advection of water masses of Pacific origin. Overall the deep water ¹⁰Be distribution is obviously not significantly affected by scavenging processes or ice melt and comparison with the density distribution suggests that ¹⁰Be can be viewed as a quasi-conservative tracer. This provides a tool for an improved understanding of the behaviour of other more particle reactive trace metals in the Southern Ocean such as ²³⁰Th: in deep waters north of the ACC/Weddell Gyre boundary (AWB) ¹⁰Be/²³⁰Th has a relatively constant value (1.7±0.3×10⁹ atoms/dpm) over a wide density range whereas south of the AWB the ratio is significantly lower (1.1±0.2×10⁹ atoms/dpm). This normalisation to ¹⁰Be corroborates that ²³⁰Th is enriched by 50% due to accumulation south of the AWB as a consequence of minimal particulate fluxes. The quasi-conservative behaviour deduced from our results also implies that ¹⁰Be can only be used as a tracer for Southern Ocean particle fluxes in the past if ocean circulation patterns and water mass residence times did not change significantly.  相似文献   

Acceleration waves,shock formation and stability in a gravitating atmosphere     

Augusto Muracchini  Tommaso Ruggeri 《Astrophysics and Space Science》1989,153(1):127-142

The shock formation in a gravitating atmosphere is studied by following the general nonlinear theory of discontinuity waves. In particular, we perform a discussion on the stability of an isothermal and isoentropic atmosphere and we evaluate, when the shock appears, the critical time and the critical height. Some numerical results for the solar and terrestrial atmospheres are also given.  相似文献   

Improving hydrological information acquisition from DEM processing in floodplains     

Augusto C. V. Getirana  Marie-Paule Bonnet  Otto C. Rotunno Filho  Webe J. Mansur 《水文研究》2009,23(3):502-514

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Multi-model calibration and combination of tropical seasonal sea surface temperature forecasts     

Luis Ricardo Lage Rodrigues  Francisco Javier Doblas-Reyes  Caio Augusto dos Santos Coelho 《Climate Dynamics》2014,42(3-4):597-616

Different combination methods based on multiple linear regression are explored to identify the conditions that lead to an improvement of seasonal forecast quality when individual operational dynamical systems and a statistical–empirical system are combined. A calibration of the post-processed output is included. The combination methods have been used to merge the ECMWF System 4, the NCEP CFSv2, the Météo-France System 3, and a simple statistical model based on SST lagged regression. The forecast quality was assessed from a deterministic and probabilistic point of view. SSTs averaged over three different tropical regions have been considered: the Niño3.4, the Subtropical Northern Atlantic and Western Tropical Indian SST indices. The forecast quality of these combinations is compared to the forecast quality of a simple multi-model (SMM) where all single models are equally weighted. The results show a large range of behaviours depending on the start date, target month and the index considered. Outperforming the SMM predictions is a difficult task for linear combination methods with the samples currently available in an operational context. The difficulty in the robust estimation of the weights due to the small samples available is one of the reasons that limit the potential benefit of the combination methods that assign unequal weights. However, these combination methods showed the capability to improve the forecast reliability and accuracy in a large proportion of cases. For example, the Forecast Assimilation method proved to be competitive against the SMM while the other combination methods outperformed the SMM when only a small number of forecast systems have skill. Therefore, the weighting does not outperform the SMM when the SMM is very skilful, but it reduces the risk of low skill situations that are found when several single forecast systems have a low skill.  相似文献   

Large scale features and energetics of the hybrid subtropical low ‘Duck’ over the Tasman Sea     

Alexandre Bernardes Pezza  Luke Andrew Garde  José Augusto Paixão Veiga  Ian Simmonds 《Climate Dynamics》2014,42(1-2):453-466

New aspects of the genesis and partial tropical transition of a rare hybrid subtropical cyclone on the eastern Australian coast are presented. The ‘Duck’ (March 2001) attracted more recent attention due to its underlying genesis mechanisms being remarkably similar to the first South Atlantic hurricane (March 2004). Here we put this cyclone in climate perspective, showing that it belongs to a class within the 1 % lowest frequency percentile in the Southern Hemisphere as a function of its thermal evolution. A large scale analysis reveals a combined influence from an existing tropical cyclone and a persistent mid-latitude block. A Lagrangian tracer showed that the upper level air parcels arriving at the cyclone’s center had been modified by the blocking. Lorenz energetics is used to identify connections with both tropical and extratropical processes, and reveal how these create the large scale environment conducive to the development of the vortex. The results reveal that the blocking exerted the most important influence, with a strong peak in barotropic generation of kinetic energy over a large area traversed by the air parcels just before genesis. A secondary peak also coincided with the first time the cyclone developed an upper level warm core, but with insufficient amplitude to allow for a full tropical transition. The applications of this technique are numerous and promising, particularly on the use of global climate models to infer changes in environmental parameters associated with severe storms.  相似文献   

Magnetostratigraphy and paleomagnetism of early and middle Miocene synorogenic strata: basement partitioning and minor block rotation in Argentine broken foreland     

Oscar Zambrano  Augusto E. Rapalini  Federico M. Dávila  Ricardo A. Astini  Cecilia M. Spagnuolo 《International Journal of Earth Sciences》2011,100(2-3):591-602

Magnetostratigraphic and paleomagnetic studies on early Andean synorogenic strata (Del Crestón Fm.), in the Famatina Belt (28.7°S, 67.5°W) clarify details of chronology that permit calculation of sedimentation rates within the broken foreland of west Argentina. The Del Crestón Fm represents the first record of broken foreland sedimentation within the southern Central Andean belt and the earliest retroarc volcanic rocks exposed several hundred kilometers from the trench. Twenty-five out of 49 sites collected along the succession presented a primary remanence, as determined through positive fold and reversal tests. Correlation of the local magnetic polarity section with the global polarity time scale indicates that the sedimentation of Del Crestón Fm started at ~16.7 Ma and continued until ~14.5 Ma. The youngest strata are represented by conglomerates bearing abundant Lower Paleozoic granite boulders indicating unroofing of the crystalline basement within the NW Sierras Pampeanas. This result supports the hypothesis of an early broken foreland stage at these latitudes of the Andes, with involvement of the basement in deformation and coeval retroarc volcanism, common attributes of flat-subduction regimes. A mean site paleomagnetic direction of Dec: 6.3°, Inc: ?43.6° (α95: 8.0°, N = 24) confirm our earlier intrepretation that the central part of the Famatina Belt within the Sierras Pampeanas did not undergo large vertical axes rotations since the Middle Miocene.  相似文献   

Contributions to the kinematics of type I tails of comets     

Karl Wurm  Augusto Mammano 《Astrophysics and Space Science》1972,18(2):273-286

Observed irregular oscillations of the ion tail axis in comets have by some authors been brought in connection with changes in the flow conditions in the solar wind. We are defending in this paper — by arguments resting on well known observations — the conception that these oscillations are caused by slight variations in the emission conditions for the ions at their source which has always its place close to the cometary nucleus. A complete renovation of the innermost tail part up to a length of a few million km (called by Hoffmeister the primary tail) and defining the tail axis can take place within a few to several hours. Shifts of this axis are becoming visible when the new tail rays finish their closure along another direction than the earlier ones.The not so rarely observed jumps in the direction of the primary tail lead in connection with the large time scale — of about 24h — for a complete closure of a ray system from an individual ion out-break to the conclusion that we should expect occasionally the existence of two (or even more) different axis to which tail rays make their closure. Some photographs of Comet Bennett 1969i seem to show such double axis.  相似文献