Late Eocene–Pliocene basin evolution in the Eastern Cordillera of northwestern Argentina (25°–26°S): regional implications for Andean orogenic wedge development     

Barbara Carrapa  Sharon Bywater‐Reyes  Peter G. DeCelles  Estelle Mortimer  George E. Gehrels 《Basin Research》2012,24(3):249-268

Important aspects of the Andean foreland basin in Argentina remain poorly constrained, such as the effect of deformation on deposition, in which foreland basin depozones Cenozoic sedimentary units were deposited, how sediment sources and drainages evolved in response to tectonics, and the thickness of sediment accumulation. Zircon U‐Pb geochronological data from Eocene–Pliocene sedimentary strata in the Eastern Cordillera of northwestern Argentina (Pucará–Angastaco and La Viña areas) provide an Eocene (ca. 38 Ma) maximum depositional age for the Quebrada de los Colorados Formation. Sedimentological and provenance data reveal a basin history that is best explained within the context of an evolving foreland basin system affected by inherited palaeotopography. The Quebrada de los Colorados Formation represents deposition in the distal to proximal foredeep depozone. Development of an angular unconformity at ca. 14 Ma and the coarse‐grained, proximal character of the overlying Angastaco Formation (lower to upper Miocene) suggest deposition in a wedge‐top depozone. Axial drainage during deposition of the Palo Pintado Formation (upper Miocene) suggests a fluvial‐lacustrine intramontane setting. By ca. 4 Ma, during deposition of the San Felipe Formation, the Angastaco area had become structurally isolated by the uplift of the Sierra de los Colorados Range to the east. Overall, the Eastern Cordillera sedimentary record is consistent with a continuous foreland basin system that migrated through the region from late Eocene through middle Miocene time. By middle Miocene time, the region lay within the topographically complex wedge‐top depozone, influenced by thick‐skinned deformation and re‐activation of Cretaceous rift structures. The association of the Eocene Quebrada del los Colorados Formation with a foredeep depozone implies that more distal foreland deposits should be represented by pre‐Eocene strata (Santa Barbara Subgroup) within the region.  相似文献   

Hierarchical star formation in M33: properties of the star-forming regions     

Nate Bastian  Barbara Ercolano  Mark Gieles 《Astrophysics and Space Science》2009,324(2-4):293-297

Star formation within galaxies occurs on multiple scales, from spiral structure, to OB associations, to individual star clusters, and often as substructure within these clusters. This multitude of scales calls for objective methods to find and classify star-forming regions, regardless of spatial size. To this end, we present an analysis of star-forming groups in the Local Group spiral galaxy M33, based on a new implementation of the Minimum Spanning Tree (MST) method. Unlike previous studies, which limited themselves to a single spatial scale, we study star-forming structures from the effective resolution limit (～20 pc) to kpc scales. Once the groups have been identified, we study their properties, such as their size and luminosity distributions, and compare these with studies of young star clusters and giant molecular clouds (GMCs). We find evidence for a continuum of star-forming group sizes, which extends into the star cluster spatial-scale regime. We do not find a characteristic scale for OB associations, unlike that found in previous studies, and we suggest that the appearance of such a scale was caused by spatial resolution and selection effects. The luminosity function of the groups is found to be well represented by a power law with an index of ?2, as has also been found for the luminosity and mass functions of young star clusters, as well as for the mass function of GMCs. Additionally, the groups follow a similar mass-radius relation as GMCs. The size distribution of the groups is best described by a log-normal distribution, the peak of which is controlled by the spatial scale probed and the minimum number of sources used to define a group. We show that within a hierarchical distribution, if a scale is selected to find structure, the resulting size distribution will have a log-normal distribution. We find an abrupt drop of the number of groups outside a galactic radius of ～4 kpc (although individual high-mass stars are found beyond this limit), suggesting a change in the structure of the star-forming interstellar medium, possibly reflected in the lack of GMCs beyond this radius. Finally, we find that the spatial distribution of H?ii regions, GMCs, and star-forming groups are all highly correlated.  相似文献   

Stability of inclined orbits of terrestrial planets in habitable zones     

Barbara Funk  Richard Schwarz 《Planetary and Space Science》2009,57(4):434-440

In long-term stability studies of terrestrial planets moving in the habitable zone (HZ) of a sun-like star, we distinguish four different configurations: (i) planets moving in binary star systems, (ii) the inner type (where the gas giant moves outside the HZ), (iii) the outer type (where the gas giant is closer to the star, than the HZ) and (iv) the Trojan type (where the gas giant moves in the HZ). Since earlier calculations indicated, that the stability of the motion in the HZ also depends on the inclination of the terrestrial planet orbits, we present a detailed numerical investigation to show correlations between the eccentricity, the mass and the distance of the giant planet for various inclinations of the terrestrial planets. The orbital stability of the HZ was examined for all four configurations stated above. While we could find hardly any stable orbits for the first three types for inclinations higher than 40^°, the Trojan planets can be stable up to an inclination of 60^°. Additionally, we could also find some stabilizing effects of the inclination for the first three types. As dynamical model we used the elliptic restricted three-body problem, which consists of two massive and one mass-less body. This allows an application to all detected and future extrasolar single planet systems.  相似文献   

The effects of spatially distributed ionisation sources on the temperature structure of H <Emphasis Type="SmallCaps">ii</Emphasis> regions     

Barbara Ercolano  Nate Bastian  Grazyna Stasińska 《Astrophysics and Space Science》2009,324(2-4):199-204

Spatially resolved studies of star-forming regions show that the assumption of spherical geometry is not realistic in most cases, with a major complication posed by the gas being ionised by multiple non-centrally located stars or star clusters. Geometrical effects including the spatial configuration of ionising sources affect the temperature and ionisation structure of these regions. We try to isolate the effects of multiple non-centrally located stars, via the construction of 3D photoionisation models using the 3D Monte Carlo photoionisation code mocassin with very simple gas density distributions, but various spatial configurations for the ionisation sources.Emission-line spectra from H?ii regions are often used to study the metallicity of star-forming regions, as well as for providing a constraint on temperatures and luminosities of the ionising sources. Empirical metallicity diagnostics must often be calibrated with the aid of photoionisation models. However, most studies so far have been carried out by assuming spherical or plane-parallel geometries, with major limitations on the allowed gas and dust density distributions and with the spatial distribution of multiple, non-centrally located ionising sources not being accounted for. We compare integrated emission-line spectra from our models and quantify any systematic errors caused by the simplifying assumption of a single, central location for all ionising sources. We find that the dependence of the metallicity indicators on the ionisation parameter causes a clear bias, due to the fact that models with a fully distributed configuration of stars always display lower ionisation parameters than their fully concentrated counterparts. The errors found imply that the geometrical distribution of ionisation sources may partly account for the large scatter in metallicities derived using model-calibrated empirical methods.  相似文献   

Spatial and time variations in critical frequencies of the ionospheric <Emphasis Type="Italic">F</Emphasis> region above the zone of equatorial earthquake preparation     

A. Kh. Depueva  A. V. Mikhailov  M. Devi  A. K. Barbara 《Geomagnetism and Aeronomy》2007,47(1):129-133

Spatial and time variations in the critical frequencies foF2 before the strong earthquake of August 15, 1963, with the magnitude M = 7.75 are analyzed. The epicenter of the earthquake was located in the vicinity of the magnetic equator in the American longitudinal sector. The data of the topside ionosonde on board Alouette-1 and of the series of ground-based ionosondes has been used for this purpose. The ground-based ionosondes made it possible to detect an insignificant anomalous decrease in foF2 within the zone of earthquake preparation a few days prior to the earthquake. This result confirms the conclusion drawn earlier on the basis of the satellite data. The modification of the ionosphere at the F-region level is more evident in the satellite than in the ground-based data. It is also noted that the character of the time variations in foF2 a day before the earthquake is similar to the so called “quiet time” Q-disturbances in the ionosphere, when the electron concentration at the F region maximum differs from the median values by more than 20% under undisturbed geophysical conditions.  相似文献   

Statistical dependence in input data of national greenhouse gas inventories: effects on the overall inventory uncertainty     

Wilfried Winiwarter  Barbara Muik 《Climatic change》2010,103(1-2):19-36

An uncertainty assessment of the Austrian greenhouse gas inventory provided the basis for this analysis. We isolated the factors that were responsible for the uncertainty observed, and compared our results with those of other countries. Uncertainties of input parameters were used to derive the uncertainty of the emission estimate. Resulting uncertainty using a Monte Carlo approach was 5.2% for the emission levels of 2005 and 2.4 percentage points for the 1990–2005 emission trend. Systematic uncertainty was not assessed. This result is in the range expected from previous experience in Austria and other countries. The determining factor for the emission level uncertainty (not the trend uncertainty) is the uncertainty associated with soil nitrous oxide N₂O emissions. Uncertainty of the soil N₂O release rate is huge, and there is no agreement even on the magnitude of the uncertainty when country comparisons are made. In other words, reporting and use of N₂O release uncertainty are also different between countries; this is important, as this single factor fully determines a country’s national greenhouse gas inventory uncertainty. Inter-country comparisons of emission uncertainty are thus unable to reveal much about a country’s inventory quality. For Austria, we also compared the results of the Monte Carlo approach to those obtained from a simpler error propagation approach, and find the latter to systematically provide lower uncertainty. The difference can be explained by the ability of the Monte Carlo approach to account for statistical dependency of input parameters, again regarding soil N₂O emissions. This is in contrast to the results of other countries, which focus less on statistical dependency when performing Monte Carlo analysis. In addition, the error propagation results depend on treatment of skewed probability distributions, which need to be translated into normal distributions. The result indicates that more attention needs to be given to identifying statistically dependent input data in uncertainty assessment.  相似文献   

Nowcasting of a supercell storm with VERA     

Stefan Schneider  Barbara Chimani  Hildegard Kaufmann  Benedikt Bica  Christoph Lotteraner  Simon Tschannett  Reinhold Steinacker 《Meteorology and Atmospheric Physics》2008,102(1-2):23-36

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Observing upper troposphere–lower stratosphere climate with radio occultation data from the CHAMP satellite     

Ulrich Foelsche  Michael Borsche  Andrea K. Steiner  Andreas Gobiet  Barbara Pirscher  Gottfried Kirchengast  Jens Wickert  Torsten Schmidt 《Climate Dynamics》2008,31(1):49-65

High quality observations of the atmosphere are particularly required for monitoring global climate change. Radio occultation (RO) data, using Global Navigation Satellite System (GNSS) signals, are well suited for this challenge. The special climate utility of RO data arises from their long-term stability due to their self-calibrated nature. The German research satellite CHAllenging Minisatellite Payload for geoscientific research (CHAMP) continuously records RO profiles since August 2001 providing the first opportunity to create RO based climatologies for a multi-year period of more than 5 years. A period of missing CHAMP data from July 3, 2006 to August 8, 2006 can be bridged with RO data from the GRACE satellite (Gravity Recovery and Climate Experiment). We have built seasonal and zonal mean climatologies of atmospheric (dry) temperature, microwave refractivity, geopotential height and pressure with 10° latitudinal resolution. We show representative results with focus on dry temperatures and compare them with analysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF). Although we have available only about 150 CHAMP profiles per day (compared to millions of data entering the ECMWF analyses) the overall agreement between 8 and 30 km altitude is in general very good with systematic differences <0.5 K in most parts of the domain. Pronounced systematic differences (exceeding 2 K) in the tropical tropopause region and above Antarctica in southern winter can almost entirely be attributed to errors in the ECMWF analyses. Errors resulting from uneven sampling in space and time are a potential error source for single-satellite climatologies. The average CHAMP sampling error for seasonal zonal means is <0.2 K, higher values occur in restricted regions and time intervals which can be clearly identified by the sampling error estimation approach we introduced (which is based on ECMWF analysis fields). The total error of this new type of temperature climatologies is estimated to be <0.5 K below 30 km. The recently launched Taiwan/U.S. FORMOSAT-3/COSMIC constellation of 6 RO satellites started to provide thousands of RO profiles per day, but already now the single-satellite CHAMP RO climatologies improve upon modern operational climatologies in the upper troposphere–lower stratosphere and can act as absolute reference climatologies for validation of more bias-sensitive climate datasets and models.  相似文献   

Asian monsoon climate during the Last Glacial Maximum: palaeo‐data–model comparisons     

Akkaneewut Chabangborn  Jenny Brandefelt  Barbara Wohlfarth 《Boreas: An International Journal of Quaternary Research》2014,43(1):220-242

The Last Glacial Maximum (LGM) (23–19 ka BP) in the Asian monsoon region is generally described as cool and dry, due to a strong winter monsoon. More recently, however, palaeo‐data and climate model simulations have argued for a more variable LGM Asian monsoon climate with distinct regional differences. We compiled, evaluated, and partly re‐assessed proxy records for the Asian monsoon region in terms of wet/dry climatic conditions based on precipitation and effective moisture, and of sea surface temperatures. The comparison of the palaeo‐data set to LGM simulations by the Climate Community System Model version 3 (CCSM3) shows fairly good agreement: a dry LGM climate in the western and northern part due to a strengthened winter monsoon and/or strengthened westerly winds and wetter conditions in equatorial areas, due to a stronger summer monsoon. Data–model discrepancies are seen in some areas and are ascribed to the fairly coarse resolution of CCSM3 and/or to uncertainties in the reconstructions. Differences are also observed between the reconstructed and simulated northern boundaries of the Intertropical Convergence Zone (ITCZ). The reconstructions estimate a more southern position over southern India and the Bay of Bengal, whereas CCSM3 simulates a more northern position. In Indochina, the opposite is the case. The palaeo‐data indicate that climatic conditions changed around 20–19 ka BP, with some regions receiving higher precipitation and some experiencing drier conditions, which would imply a distinct shift in summer monsoon intensity. This shift was probably triggered by the late LGM sea‐level rise, which led to changes in atmosphere–ocean interactions in the Indian Ocean. The overall good correspondence between reconstructions and CCSM3 suggests that CCSM3 simulates LGM climate conditions over subtropical and tropical areas fairly well. The few high‐resolution qualitative and quantitative palaeo‐records available for the large Asian monsoon region make reconstructions however still uncertain.  相似文献   

The role of negative CO2 emissions for reaching 2 °C—insights from integrated assessment modelling     

Detlef P. van Vuuren  Sebastiaan Deetman  Jasper van Vliet  Maarten van den Berg  Bas J. van Ruijven  Barbara Koelbl 《Climatic change》2013,118(1):15-27

Limiting climate change to 2 °C with a high probability requires reducing cumulative emissions to about 1600 GtCO₂ over the 2000–2100 period. This requires unprecedented rates of decarbonization even in the short-run. The availability of the option of net negative emissions, such as bio-energy with carbon capture and storage (BECCS) or reforestation/afforestation, allows to delay some of these emission reductions. In the paper, we assess the demand and potential for negative emissions in particular from BECCS. Both stylized calculations and model runs show that without the possibility of negative emissions, pathways meeting the 2 °C target with high probability need almost immediate emission reductions or simply become infeasible. The potential for negative emissions is uncertain. We show that negative emissions from BECCS are probably limited to around 0 to 10 GtCO₂/year in 2050 and 0 to 20 GtCO₂/year in 2100. Estimates on the potential of afforestation options are in the order of 0–4 GtCO₂/year. Given the importance and the uncertainty concerning BECCS, we stress the importance of near-term assessments of its availability as today’s decisions has important consequences for climate change mitigation in the long run.  相似文献