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21.
Jean-Alix Barrat Akira Yamaguchi Claire Bollinger Marcel Bohn 《Geochimica et cosmochimica acta》2010,74(21):6218-6231
The eucrites and diogenites are meteorites that probably originate from asteroid 4-Vesta. The upper part of the crust of this body is certainly composed of eucrites which are basaltic or gabbroic rocks. Diogenites are ultramafic cumulates whose relationships with eucritic lithologies are unknown. Here, we show that the orthopyroxenes of some diogenites display very deep negative Eu anomalies (Eu/Eu∗ close to 0.1 or lower). The contamination of the parental magmas of diogenites by melts derived by partial melting of the eucritic crust can satisfactorily explain the range of the Eu anomalies displayed by diogenites. Thus, these anomalies are the first firm indication that parental melts of diogenites have intruded the eucritic crust, and consequently are younger than eucrites. 相似文献
22.
Claire Kain Christopher Gomez Patrick Wassmer Franck Lavigne Deirdre Hart 《New Zealand geographer》2014,70(3):165-178
The 2004 tsunami transformed the coast of Indonesia. This research investigates a sand dune area in Lampuuk, Sumatra, that was scoured by tsunami flow. We assessed geomorphology one‐year post‐event and examine the timescale of vegetation recovery. Ground Penetrating Radar (GPR) evidence shows an eroded succession of thin dipping units, overlain by aeolian layers 0 to 50 cm thick. Incipient dunes were absent, indicating limited dune rebuilding at one‐year post‐tsunami, possibly resulting from channelised airflow and the absence of vegetation. Recolonisation by vegetation was initially limited but progressed rapidly between 2005 and 2011, highlighting the temporal non‐linearity of recovery processes. 相似文献
23.
Elaine?R.?MilesEmail author Claire?M.?Spillman John?A.?Church Peter?C.?McIntosh 《Climate Dynamics》2014,43(7-8):2131-2145
Advanced warning of extreme sea level events is an invaluable tool for coastal communities, allowing the implementation of management policies and strategies to minimise loss of life and infrastructure damage. This study is an initial attempt to apply a dynamical coupled ocean–atmosphere model to the prediction of seasonal sea level anomalies (SLA) globally for up to 7 months in advance. We assess the ability of the Australian Bureau of Meteorology’s operational seasonal dynamical forecast system, the Predictive Ocean Atmosphere Model for Australia (POAMA), to predict seasonal SLA, using gridded satellite altimeter observation-based analyses over the period 1993–2010 and model reanalysis over 1981–2010. Hindcasts from POAMA are based on a 33-member ensemble of seasonal forecasts that are initialised once per month for the period 1981–2010. Our results show POAMA demonstrates high skill in the equatorial Pacific basin and consistently exhibits more skill globally than a forecast based on persistence. Model predictability estimates indicate there is scope for improvement in the higher latitudes and in the Atlantic and Southern Oceans. Most characteristics of the asymmetric SLA fields generated by El-Nino/La Nina events are well represented by POAMA, although the forecast amplitude weakens with increasing lead-time. 相似文献
24.
Understanding the impact of past climatic changes on landscape stability is crucial in order to predict and mitigate the effects of future changes. However, in arid and semi‐arid environments, reconstructions are often hampered by a poor understanding of the relationship between sediment deposition and climate. We present here data from central Texas, a region that is sensitive to environmental change but has received relatively little attention. The study integrates a chronology of 29 optically stimulated luminescence (OSL) ages from six sedimentary sites in a range of depositional contexts with a 19 000 a climate record derived from pollen extracted from the adjacent Boriack Bog. By comparing the two records, we aimed to assess the relationship between climate change and geomorphic activity. Data show that extensive aeolian and colluvial deposition occurred during the mid to late Holocene, with sedimentation generally increasing during more arid phases. However, a number of depositional events on slopes were associated with moister episodes, and sediment was also deposited in a summit setting immediately after phases of increased precipitation. Linkages between climate change and geomorphic response were therefore complex, being controlled by both sediment supply and transport energy. The climatic fluctuations identified in the Boriack Bog record highlight the sensitivity of central Texas to environmental change, while disparities in conditions recorded between it and other palaeoenvironmental sites in the southern USA emphasise the need for further work in order to enhance understanding of landscape sedimentary response to climate. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
25.
Pedro Augusto Alastair C. Edge Claire J. Chandler 《Monthly notices of the Royal Astronomical Society》2006,367(1):366-374
We present multifrequency, multi-epoch radio imaging of the complex radio source B2151+174 in the core of the cluster, Abell 2390 ( z ≃ 0.23) . From new and literature data, we conclude that the Faranoff–Riley type II (FRII)-powerful radio source is the combination of a compact, core-dominated 'medium-sized symmetric object' (MSO) with a more extended, steeper spectrum mini-halo. B2151+174 is unusual in a number of important aspects. (i) It is one of the most compact and flat spectrum sources in a cluster core known; (ii) it shows a complex, compact twin-jet structure in a north–south orientation; (iii) the orientation of the jets is 45° misaligned with apparent structure (ionization cones and dust disc) of the host galaxy on larger scales. Since the twin-jet of the MSO has its northern half with an apparent 'twist', it might be that precession of the central supermassive black hole explains this misalignment. B2151+174 may be an example of the early stage (103 –104 yr duration) of a 'bubble' being blown into the intracluster medium where the plasma has yet to expand. 相似文献
26.
Itziar De Gregorio-Monsalvo Claire J. Chandler José F. Gómez Thomas B. H. Kuiper José M. Torrelles Guillem Anglada 《Astrophysics and Space Science》2005,295(1-2):65-70
We present a study of the structure and dynamics of the star-forming region B1-IRS (IRAS 03301+3057) using the properties of different molecules at high angular resolution (4). We have used VLA observations of NH3, CCS, and H2O masers at 1 cm. CCS emission shows three clumps around the central source, with a velocity gradient from red to blue-shifted velocities towards the protostar, probably due to the interaction with outflowing material. Water maser emission is elongated in the same direction as a reflection nebula detected at 2 m by 2MASS, with the maser spots located in a structure of some hundreds of AU from the central source, possibly tracing a jet. We propose a new outflow model to explain all our observations, consisting of a molecular outflow near the plane of the sky. Ammonia emission is extended and anticorrelated with CCS. We have detected for the first time this anticorrelation at small scales (1400 AU) in a star-forming region. 相似文献
27.
Brendon Blue Claire Gregory Kiely McFarlane Marc Tadaki Petra van Limburg‐Meijer Nick Lewis 《New Zealand geographer》2012,68(1):62-66
The fair and effective governance of freshwater is an increasingly prominent issue in New Zealand. Emerging from a complex of cultural, economic and biophysical narratives, freshwater geographies are multiple, varied and increasingly acknowledged as worthy of interdisciplinary scrutiny. In this commentary, we reflect on a series of generative spaces that we – as group of postgraduate geographers (plus supporting staff) – created to engage with the multiplicity of freshwater meanings both within and beyond the academy. Through this evolving epistemic‐political project, we significantly reframed our own understandings about what freshwater ‘is’ and how it ought to be governed. By pursuing a deeper understanding of how the world gets made, we expand our ability to know and make it differently. 相似文献
28.
Marc Poumadère Claire Mays Gabriela Pfeifle Athanasios T. Vafeidis 《Climatic change》2008,91(1-2):123-143
Risk policy and public attitudes appear disconnected from research predicting warmer climate partially due to human activity. To step out of this stalled situation, a worst case scenario of a 5- to 6-m sea level rise (SLR) induced by the collapse of the WAIS and occurring during the period 2030–2130 is constructed and applied to the Rhone delta. Physical and socio-economic scenarios developed with data from the Rhone delta context are developed and submitted to stakeholders for a day-long workshop. Group process analysis shows a high level of trust and cooperation mobilized to face the 5–6 m SLR issue, despite potentially diverging interests. Two sets of recommendations stem from the scenario workshop. A conservative “wait and see” option is decided when the risk of the WAIS collapse is announced in 2030. After WAIS collapse generates an effective 1 m SLR rise by 2050, decisions are taken for total retreat and rendering of the Rhone delta to its hydrological function. The transposition of these results into present-day policy decisions could be considered. The methodology developed here could be applied to other risk objects and situations, and serve for policy exercises and crisis prevention. 相似文献
29.
Yuan Lian Mark I. Richardson Claire E. Newman Christopher Lee Anthony D. Toigo Michael A. Mischna Jean-Michel Campin 《Icarus》2012,218(2):1043-1070
We investigate the ability of modern general circulation models (GCMs) to simulate transport in the martian atmosphere using measurements of argon as a proxy for the transport processes. Argon provides the simplest measure of transport as it is a noble gas with no sinks or sources on seasonal timescales. Variations in argon result solely from ‘freeze distillation’, as the atmosphere condenses at the winter poles, and from atmospheric transport. Comparison of all previously published models when rescaled to a common definition of the argon enhancement factor (EF) suggest that models generally do a poor job in predicting the peak enhancement in southern winter over the winter pole – the time when the capability of the model transport approaches are most severely tested. Despite observed peak EF values of ~6, previously published model predictions peaked at EF values of only 2–3. We introduce a new GCM that provides a better treatment of mass conservation within the dynamical core, includes more sophisticated tracer transport approaches, and utilizes a cube–sphere grid structure thus avoiding the grid-point convergence problem at the pole that exists for most current Mars GCMs. We describe this model – the Ashima Research/Massachusetts Institute of Technology Mars General Circulation Model (Ashima/MIT Mars GCM) and use it to demonstrate the significant sensitivity of peak EF to the choices of transport approach for both tracers and heat. We obtain a peak EF of 4.75 which, while over 50% higher than any prior model, remains well short of the observed value. We show that the polar EF value in winter is primarily determined by the competition between two processes: (1) mean meridional import of lower-latitude air not enriched in argon and (2) the leakage of enriched argon out of the polar column by eddies in the lowest atmospheric levels. We suggest possibilities for improving GCM representation of the CO2 cycle and the general circulation that may further improve the simulation of the argon cycle. We conclude that current GCMs may be insufficient for detailed simulation of transport-sensitive problems like the water cycle and potentially also the dust cycle. 相似文献
30.
The reaction of CN? with cyanoacetylene (HC3N), has been studied as a function of the HC3N pressure in a quadrupole tandem mass spectrometer. The mass spectra revealed the fast depletion of the CN? parent ion and formation of larger anions of rapidly growing size. Most of the ions observed were found to belong to two series of products: (HC3N)x·C2p+1N? and (HC3N)x·C2pN? resulting from the sequential additions of HC3N molecules and loss of HCN or HCCN molecules. The mechanism and energetics of the first two reaction steps are briefly discussed. The laboratory data are compared with those from the Cassini CAPS-ELS spectrometer. It is believed that the reactions observed could account for the growth of anions in Titan’s ionosphere. 相似文献