Modes of variability of Southern Hemisphere atmospheric circulation estimated by AGCMs     

Simon Grainger  Carsten S. Frederiksen  Xiaogu Zheng  David Fereday  Chris K. Folland  Emilia K. Jin  James L. Kinter  Jeff R. Knight  Siegfried Schubert  Jozef Syktus 《Climate Dynamics》2011,36(3-4):473-490

The seasonal mean variability of the atmospheric circulation is affected by processes with time scales from less than seasonal to interannual or longer. Using monthly mean data from an ensemble of Atmospheric General Circulation Model (AGCM) realisations, the interannual variability of the seasonal mean is separated into intraseasonal, and slowly varying components. For the first time, using a recently developed method, the slowly varying component in multiple AGCM ensembles is further separated into internal and externally forced components. This is done for Southern Hemisphere 500?hPa geopotential height from five AGCMs in the CLIVAR International Climate of the Twentieth Century project for the summer and winter seasons. In both seasons, the intraseasonal and slow modes of variability are qualitatively well reproduced by the models when compared with reanalysis data, with a relative metric finding little overall difference between the models. The Southern Annular Mode (SAM) is by far the dominant mode of slowly varying internal atmospheric variability. Two slow-external modes of variability are related to El Ni?o-Southern Oscillation (ENSO) variability, and a third is the atmospheric response to trends in external forcing. An ENSO-SAM relationship is found in the model slow modes of variability, similar to that found by earlier studies using reanalysis data. There is a greater spread in the representation of model slow-external modes in winter than summer, particularly in the atmospheric response to external forcing trends. This may be attributable to weaker external forcing constraints on SH atmospheric circulation in winter.  相似文献   

Exhumation and uplift of the Sierras Pampeanas: preliminary implications from K–Ar fault gouge dating and low-T thermochronology in the Sierra de Comechingones (Argentina)     

Stefan Löbens  Frithjof A. Bense  Klaus Wemmer  István Dunkl  Carlos H. Costa  Paul Layer  Siegfried Siegesmund 《International Journal of Earth Sciences》2011,100(2-3):671-694

The Sierras Pampeanas in central and north-western Argentina constitute a distinct morphotectonic feature between 27°S and 33°S. The last stage of uplift and deformation in this area are interpreted to be closely related to the Andean flat-slab subduction of the Nazca plate beneath the South American plate. K–Ar fault gouge dating and low-temperature thermochronology along two transects within the Sierra de Comechingones reveal a minimum age for the onset of brittle deformation about 340 Ma, very low exhumation rates since Late Paleozoic time, as well as a total exhumation of about 2.3 km since the Late Cretaceous. New Ar–Ar ages (7.54–1.91 Ma) of volcanic rocks from the San Luis volcanic belt support the eastward propagation of the flat-slab magmatic front, confirming the onset of flat-slab related deformation in this region at 11.2 Ma. Although low-temperature thermochronology does not clearly constrain the signal of the Andean uplift, it is understood that the current structural relief related to the Comechingones range has been achieved after the exhumation of both fault walls (circa 80–70 Ma).  相似文献   

Large-Eddy Simulations of Surface Heterogeneity Effects on the Convective Boundary Layer During the LITFASS-2003 Experiment   总被引：3，自引：3，他引：0  

Bj?rn Maronga  Siegfried Raasch 《Boundary-Layer Meteorology》2013,146(1):17-44

We investigate the impact of observed surface heterogeneities during the LITFASS-2003 experiment on the convective boundary layer (CBL). Large-eddy simulations (LES), driven by observed near-surface sensible and latent heat fluxes, were performed for the diurnal cycle and compare well with observations. As in former studies of idealized one- and two-dimensional heterogeneities, secondary circulations developed that are superimposed on the turbulent field and that partly take over the vertical transport of heat and moisture. The secondary circulation patterns vary between local and roll-like structures, depending on the background wind conditions. For higher background wind speeds, the flow feels an effective surface heat-flux pattern that derives from the original pattern by streamwise averaging. This effective pattern generates a roll-like secondary circulation with roll axes along the mean boundary-layer wind direction. Mainly the upstream surface conditions control the secondary circulation pattern, where the fetch increases with increasing background wind speed. Unlike the entrainment flux that appears to be slightly decreased compared to the homogeneously-heated CBL, the vertical flux of sensible heat appears not to be modified in the mixed layer, while the vertical flux of latent heat shows different responses to secondary circulations. The study illustrates that sufficient time averaging and ensemble averaging is required to separate the heterogeneity-induced signals from the raw LES turbulence data. This might be an important reason why experiments over heterogeneous terrain in the past did not give any clear evidence of heterogeneity-induced effects.  相似文献   

Editorial to the topical collection in Environmental Earth Sciences “Stone in the architectural heritage: from quarry to monuments—environment,exploitation, properties and durability”     

Siegfried Siegesmund  Luís Sousa  Rubén Alfonso López-Doncel 《Environmental Earth Sciences》2018,77(21):730

  相似文献   

Fault gouge analyses: K–Ar illite dating,clay mineralogy and tectonic significance—a study from the Sierras Pampeanas,Argentina     

Frithjof A. Bense  Klaus Wemmer  Stefan Löbens  Siegfried Siegesmund 《International Journal of Earth Sciences》2014,103(1):189-218

We introduce a method for the detailed interpretation of K–Ar illite fine-fraction ages of fault gouges from non-sedimentary host rocks. Ages are cross-evaluated with several independent parameters, e.g. illite crystallinity, illite polytype quantification, grain size, mineralogical observations, K–Ar muscovite and biotite host-rock cooling ages as well as low-temperature thermochronological data (AFT, AHe, ZHe). This interpretation approach is applied to a regional study in order to constrain the ‘deformation path’ of the Eastern Sierras Pampeanas in NW Argentina. In the course of this study, a large number of gouge-bearing fault zones were systematically sampled and analysed. Obtained K–Ar illite fine-fraction ages range from Devonian to Cretaceous times, documenting a long-lasting brittle fault activity in this region. Ages >320 Ma are synchronous with a period of intra-Carboniferous compressional tectonism, whereas Permo-Triassic ages are contemporaneous to a flat-slab subduction episode of the Farallon plate beneath the South American plate. Middle to Late Permian and Early Triassic ages as well as Early Jurassic to Middle Cretaceous ages correlate with extensional tectonics in this region. Additionally, K–Ar illite ages reveal a propagation of brittle deformation from north to south in the Sierras de Córdoba and San Luis. Data integrity and consistency with other chronometers and geological evidence show that the here suggested interpretation is valid and can provide a powerful tool to evaluate cooling and deformation histories. Despite of that, we could show that the reliability of fault gouge data strongly depends on the regional cooling.  相似文献   

Granitic dimensional stones in Uruguay: evaluation and assessment of potential resources   总被引：1，自引：1，他引：0  

Manuela Morales Demarco  Pedro Oyhantçabal  Karl-Jochen Stein  Siegfried Siegesmund 《Environmental Earth Sciences》2013,69(4):1397-1438

In Uruguay commercial granite varieties comprise mafic rocks, granitoids, and syenitoids. There is a long tradition in Uruguay, as well as worldwide, of using dimensional stones in architecture and art, specially granitic ones. Some of the present applications of these dimensional stones are as façade cladding, countertops, and outdoor and indoor floor slabs. The color spectrum of the Uruguayan granitic dimensional stones varies from black to light gray, covering a wide variety of red and pink and minor greenish-gray. The décor of these granitic dimensional stones is mainly determined by their fabric, fundamentally the grain size and the color distribution between the different minerals that compose the rocks. In the present research the most important commercial granites were sampled to analyze their petrography and petrophysical properties. A detailed structural analysis has been performed in several deposits, as well as the application of the software 3D Block Expert for modeling the possible raw block size distribution. Other factors controlling the mining viability of the deposits were also studied (e.g., homogeneity/heterogeneity of color and décor) and the possible reserves were calculated.  相似文献   

Microcracking in calcite and dolomite marble: microstructural influences and effects on properties     

Victoria Shushakova  Edwin R. Fuller Jr.  Siegfried Siegesmund 《Environmental Earth Sciences》2013,69(4):1263-1279

Microstructure‐based finite-element analysis with a microcracking algorithm was used to simulate an actual degradation phenomenon of marble structures, i.e., microcracking. Both microcrack initiation and crack propagation were characterized, as were their dependence on lattice preferred orientation (LPO), grain shape preferred orientation (SPO), grain size, marble composition (calcite and dolomite) and grain‐boundary fracture toughness. Two LPOs were analyzed: a random orientation distribution function and an orientation distribution function with strong directional crystalline texture generated from a March–Dollase distribution. Three SPOs were considered: equiaxed grains; elongated grains and a mixture of equiaxed and elongated grains. Three different grain sizes were considered: fine grains of order 200 μm (only calcitic marble); medium size grains of order 1 mm (calcitic and dolomitic marbles); and large grains of order 2 mm (only dolomitic marble). The fracture surface energy for the grain boundaries, γ_ig, was chosen to be 20 and 40 % of the fracture surface energy of a grain, γ_xtal, so that both intergranular and transgranular fracture were possible. Studies were performed on these idealized marble microstructures to elucidate the range of microcracking responses. Simulations were performed for both heating and cooling by 50 °C in steps of 1 °C. Microcracking results were correlated with the thermoelastic responses, which are indicators related to degradation. The results indicate that certain combinations of LPO, SPO, grain size, grain‐boundary fracture toughness and marble composition have a significant influence on the thermal-elastic response of marble. Microstructure with the smallest grain size and the highest degree of SPO and LPO had less of a tendency to microcrack. Additionally, with increasing SPO and LPO microcracking becomes more spatially anisotropic. A significant observation for all microstructures was an asymmetry in microcracking upon heating and cooling: more microcracking was observed upon cooling than upon heating. Given an identical microstructure and crystallographic texture, calcite showed larger thermal stresses than dolomite, had an earlier onset of microcracking upon heating and cooling, and a greater microcracked area at a given temperature differential. Thermal expansion coefficients with and without microcracking were also determined.  相似文献   

Refinement of Near Earth Asteroids’ orbital elements via simultaneous measurements by two observers     

Siegfried Eggl 《Celestial Mechanics and Dynamical Astronomy》2011,109(3):211-228

The aspects of triangulation of Near Earth Asteroids by two arbitrarily positioned observers (one spaceborne and the other Earth-bound, as well as both spaceborne) are being investigated, and the resulting orbital elements are compared to those gained through common orbital determination and refinement techniques. The main advantages of the method proposed in this work are, that given the approximate position of an asteroid, high quality orbital elements can be acquired very rapidly using two observations only.  相似文献   

Jesenice—A new meteorite fall from Slovenia     

Addi BISCHOFF  Miha JERSEK  Thomas GRAU  Breda MIRTIC  Ulrich OTT  Jan KUČERA  Marian HORSTMANN  Matthias LAUBENSTEIN  Siegfried HERRMANN  Zdeněk ŘANDA  Marc WEBER  Gerd HEUSSER 《Meteoritics & planetary science》2011,46(6):793-804

Abstract– On April 9, 2009, at 3:00 CEST, a very bright fireball appeared over Carinthia and the Karavanke Mountains. The meteoroid entered the atmosphere at a very steep angle and disintegrated into a large number of objects. Two main objects were seen as separate fireballs up to an altitude of approximately 5 km, and witnesses reported loud explosions. Three stones were found with a total weight of approximately 3.611 kg. The measured activity of short‐lived cosmogenic radionuclides clearly indicates that two specimens result from a very recent meteorite fall. All cosmogenic radionuclide concentrations suggest a rather small preatmospheric radius of <20 cm; a nominal cosmic‐ray exposure age based on ²¹Ne is approximately 4 Ma, but the noble gas and radionuclide results in combination indicate a complex irradiation. Jesenice is a highly recrystallized rock with only a few relic chondrules visible in hand specimen and thin section. The texture, the large grain size of plagioclase, and the homogeneous compositions of olivines and pyroxenes clearly indicate that Jesenice is a L6 chondrite. The bulk composition of Jesenice is very close to the published average element concentration for L ordinary chondrites. The chondrite is weakly shocked (S3) as indicated by the undulatory extinction in olivine and plagioclase and the presence of planar fractures in olivine. Being weakly shocked and with gas retention ages of >1.7 Ga (⁴He) and approximately 4.3 Ga (⁴⁰Ar), Jesenice seems not to have been strongly affected by the catastrophic disruption of the L‐chondrite parent body approximately 500 Ma ago.  相似文献   

Contemporaneous assembly of Western Gondwana and final Rodinia break-up: Implications for the supercontinent cycle   总被引：2，自引：0，他引：2  

Sebastián Oriolo  Pedro Oyhantçabal  Klaus Wemmer  Siegfried Siegesmund 《地学前缘(英文版)》2017,8(6):1431-1445

Geological, geochronological and isotopic data are integrated in order to present a revised model for the Neoproterozoic evolution of Western Gondwana. Although the classical geodynamic scenario assumed for the period 800–700 Ma is related to Rodinia break-up and the consequent opening of major oceanic basins, a significantly different tectonic evolution can be inferred for most Western Gondwana cratons. These cratons occupied a marginal position in the southern hemisphere with respect to Rodinia and recorded subduction with back-arc extension, island arc development and limited formation of oceanic crust in internal oceans. This period was thus characterized by increased crustal growth in Western Gondwana, resulting from addition of juvenile continental crust along convergent margins. In contrast, crustal reworking and metacratonization were dominant during the subsequent assembly of Gondwana. The Río de la Plata, Congo-São Francisco, West African and Amazonian cratons collided at ca. 630–600 Ma along the West Gondwana Orogen. These events overlap in time with the onset of the opening of the Iapetus Ocean at ca. 610–600 Ma, which gave rise to the separation of Baltica, Laurentia and Amazonia and resulted from the final Rodinia break-up. The East African/Antarctic Orogen recorded the subsequent amalgamation of Western and Eastern Gondwana after ca. 580 Ma, contemporaneously with the beginning of subduction in the Terra Australis Orogen along the southern Gondwana margin. However, the Kalahari Craton was lately incorporated during the Late Ediacaran–Early Cambrian. The proposed Gondwana evolution rules out the existence of Pannotia, as the final Gondwana amalgamation postdates latest connections between Laurentia and Amazonia. Additionally, a combination of introversion and extroversion is proposed for the assembly of Gondwana. The contemporaneous record of final Rodinia break-up and Gondwana assembly has major implications for the supercontinent cycle, as supercontinent amalgamation and break-up do not necessarily represent alternating episodic processes but overlap in time.  相似文献