High-resolution climate simulation of the last glacial maximum     

Seong-Joong Kim  Thomas J. Crowley  David J. Erickson  Bala Govindasamy  Phillip B. Duffy  Bang Yong Lee 《Climate Dynamics》2008,31(1):1-16

The climate of the last glacial maximum (LGM) is simulated with a high-resolution atmospheric general circulation model, the NCAR CCM3 at spectral truncation of T170, corresponding to a grid cell size of roughly 75 km. The purpose of the study is to assess whether there are significant benefits from the higher resolution simulation compared to the lower resolution simulation associated with the role of topography. The LGM simulations were forced with modified CLIMAP sea ice distribution and sea surface temperatures (SST) reduced by 1°C, ice sheet topography, reduced CO₂, and 21,000 BP orbital parameters. The high-resolution model captures modern climate reasonably well, in particular the distribution of heavy precipitation in the tropical Pacific. For the ice age case, surface temperature simulated by the high-resolution model agrees better with those of proxy estimates than does the low-resolution model. Despite the fact that tropical SSTs were only 2.1°C less than the control run, there are many lowland tropical land areas 4–6°C colder than present. Comparison of T170 model results with the best constrained proxy temperature estimates (noble gas concentrations in groundwater) now yield no significant differences between model and observations. There are also significant upland temperature changes in the best resolved tropical mountain belt (the Andes). We provisionally attribute this result in part as resulting from decreased lateral mixing between ocean and land in a model with more model grid cells. A longstanding model-data discrepancy therefore appears to be resolved without invoking any unusual model physics. The response of the Asian summer monsoon can also be more clearly linked to local geography in the high-resolution model than in the low-resolution model; this distinction should enable more confident validation of climate proxy data with the high-resolution model. Elsewhere, an inferred salinity increase in the subtropical North Atlantic may have significant implications for ocean circulation changes during the LGM. A large part of the Amazon and Congo Basins are simulated to be substantially drier in the ice age—consistent with many (but not all) paleo data. These results suggest that there are considerable benefits derived from high-resolution model regarding regional climate responses, and that observationalists can now compare their results with models that resolve geography at a resolution comparable to that which the proxy data represent.  相似文献   

Relative clustering and the joint halo occupation distribution of red sequence and blue-cloud galaxies in COMBO-17     

P. Simon  M. Hetterscheidt  C. Wolf  K. Meisenheimer  H. Hildebrandt  P. Schneider  M. Schirmer  T. Erben 《Monthly notices of the Royal Astronomical Society》2009,398(2):807-831

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The STAGES view of red spirals and dusty red galaxies: mass-dependent quenching of star formation in cluster infall     

Christian Wolf  Alfonso Aragón-Salamanca  Michael Balogh  Marco Barden  Eric F. Bell  Meghan E. Gray  Chien Y. Peng  David Bacon  Fabio D. Barazza  Asmus Böhm  John A. R. Caldwell  Anna Gallazzi  Boris Häußler  Catherine Heymans  Knud Jahnke  Shardha Jogee  Eelco van Kampen  Kyle Lane  Daniel H. McIntosh  Klaus Meisenheimer  Casey Papovich  Sebastian F. Sánchez  y Taylor  Lutz Wisotzki  Xianzhong Zheng 《Monthly notices of the Royal Astronomical Society》2009,393(4):1302-1323

We investigate the properties of optically passive spirals and dusty red galaxies in the A901/2 cluster complex at redshift ∼0.17 using rest-frame near-ultraviolet–optical spectral energy distributions, 24-μm infrared data and Hubble Space Telescope morphologies from the STAGES data set. The cluster sample is based on COMBO-17 redshifts with an rms precision of  σ _cz ≈ 2000 km s⁻¹  . We find that 'dusty red galaxies' and 'optically passive spirals' in A901/2 are largely the same phenomenon, and that they form stars at a substantial rate, which is only four times lower than that in blue spirals at fixed mass. This star formation is more obscured than in blue galaxies and its optical signatures are weak. They appear predominantly in the stellar mass range of  log  M _*/M_⊙=[10, 11]  where they constitute over half of the star-forming galaxies in the cluster; they are thus a vital ingredient for understanding the overall picture of star formation quenching in clusters. We find that the mean specific star formation rate (SFR) of star-forming galaxies in the cluster is clearly lower than in the field, in contrast to the specific SFR properties of blue galaxies alone, which appear similar in cluster and field. Such a rich red spiral population is best explained if quenching is a slow process and morphological transformation is delayed even more. At  log  M _*/M_⊙ < 10  , such galaxies are rare, suggesting that their quenching is fast and accompanied by morphological change. We note that edge-on spirals play a minor role; despite being dust reddened they form only a small fraction of spirals independent of environment.  相似文献   

A multiphysics and multiscale software environment for modeling astrophysical systems     

Simon Portegies Zwart  Steve McMillan  Stefan Harfst  Derek Groen  Michiko Fujii  Breanndán Ó Nualláin  Evert Glebbeek  Douglas Heggie  James Lombardi  Piet Hut  Vangelis Angelou  Sambaran Banerjee  Houria Belkus  Tassos Fragos  John Fregeau  Evghenii Gaburov  Rob Izzard  Mario Jurić  Stephen Justham  Andrea Sottoriva  Marcel Zemp 《New Astronomy》2009,14(4):369-378

We present MUSE, a software framework for combining existing computational tools for different astrophysical domains into a single multiphysics, multiscale application. MUSE facilitates the coupling of existing codes written in different languages by providing inter-language tools and by specifying an interface between each module and the framework that represents a balance between generality and computational efficiency. This approach allows scientists to use combinations of codes to solve highly coupled problems without the need to write new codes for other domains or significantly alter their existing codes. MUSE currently incorporates the domains of stellar dynamics, stellar evolution and stellar hydrodynamics for studying generalized stellar systems. We have now reached a “Noah’s Ark” milestone, with (at least) two available numerical solvers for each domain. MUSE can treat multiscale and multiphysics systems in which the time- and size-scales are well separated, like simulating the evolution of planetary systems, small stellar associations, dense stellar clusters, galaxies and galactic nuclei. In this paper we describe three examples calculated using MUSE: the merger of two galaxies, the merger of two evolving stars, and a hybrid N-body simulation. In addition, we demonstrate an implementation of MUSE on a distributed computer which may also include special-purpose hardware, such as GRAPEs or GPUs, to accelerate computations. The current MUSE code base is publicly available as open source at http://muse.li.  相似文献   

Optimal identification of potential-radiation hydrodynamics for moored floating structures—a new general approach in state space     

《Ocean Engineering》2004,31(14-15):1859-1914

In this paper, a new state-space model of the potential-radiation hydrodynamics in moored ocean engineering floating structures and its parameter identification are presented. The raw data for this goal are the added mass and potential-damping matrices in frequency-discrete domain.In a preliminary study of existing approaches in the literature, two mathematical models and their estimation are comparatively analysed in detail. These served in the development of the new approach that shares certain main advantages of the previous approaches.The model is identified in a least-squares sense using a weighted norm and a free control parameter to accomplish a trade-off between quality and stability. This reduces numerical instability problems and also keeps the analytical and computational benefits of a parametric state-space model. The model can be conveniently expressed in any usual canonical form in state space.The application of the model acceptably accurate reproduces the behaviour of the potential-radiation hydrodynamic forces in time. Case studies involving a semisubmersible and buoys are shown to demonstrate the features of the proposed approach.  相似文献   

The dark matter environment of the Abell 901/902 supercluster: a weak lensing analysis of the HST STAGES survey     

Catherine Heymans  Meghan E. Gray  Chien Y. Peng  Ludovic Van Waerbeke  Eric F. Bell  Christian Wolf  David Bacon  Michael Balogh  Fabio D. Barazza  Marco Barden  Asmus Böhm  John A. R. Caldwell  Boris Häußler  Knud Jahnke  Shardha Jogee  Eelco van Kampen  Kyle Lane  Daniel H. McIntosh  Klaus Meisenheimer  Yannick Mellier  Sebastian F. Sánchez  y N. Taylor  Lutz Wisotzki  Xianzhong Zheng 《Monthly notices of the Royal Astronomical Society》2008,385(3):1431-1442

We present a high-resolution dark matter reconstruction of the   z = 0.165  Abell 901/902 supercluster from a weak lensing analysis of the Hubble Space Telescope STAGES survey. We detect the four main structures of the supercluster at high significance, resolving substructure within and between the clusters. We find that the distribution of dark matter is well traced by the cluster galaxies, with the brightest cluster galaxies marking out the strongest peaks in the dark matter distribution. We also find a significant extension of the dark matter distribution of Abell 901a in the direction of an infalling X-ray group Abell 901α. We present mass, mass-to-light and mass-to-stellar mass ratio measurements of the structures and substructures that we detect. We find no evidence for variation of the mass-to-light and mass-to-stellar mass ratio between the different clusters. We compare our space-based lensing analysis with an earlier ground-based lensing analysis of the supercluster to demonstrate the importance of space-based imaging for future weak lensing dark matter 'observations'.  相似文献   

On the extraction of extended structure from Herschel-SPIRE scanning observations in the presence of 1/f noise     

B. Sibthorpe  P. Chanial  T. J. Waskett  M. J. Griffin 《Monthly notices of the Royal Astronomical Society》2008,388(4):1787-1791

We present results from a study of the impact of uncorrelated 1/ f noise on the extraction of spatial structure, on a range of scales, from sky mapping observations made using the Herschel-SPIRE (the spectral and photometric imaging receiver) photometer in the scan-map mode. These studies were carried out using a detailed instrument simulator, and the output reduced using the map-making algorithm to be implemented in the SPIRE data pipeline. The influence of source size scale, telescope-scanning rate and 1/ f noise knee frequency is investigated, and operational bounds to the expected losses are presented, using the case of zero 1/ f (white) noise as a benchmark. Both cross-linked and non-cross-linked observing options are studied. The results presented here represent the best current estimate of the sensitivity of the SPIRE photometer to emission on arbitrary scales. The data presented are general and scalable to any SPIRE observation made using the scanning mode.  相似文献   

Detrital zircon U-Pb ages in the Rif Belt (northern Morocco): Paleogeographic implications     

《Gondwana Research》2019

Detrital zircon U-Pb age distributions in Mesozoic and Cenozoic rocks from the External Rif and Maghrebian Flysch Complex (including the so-called Mauretanian internal flysch units) are very similar, strongly suggesting that the External Rif and the entire Maghrebian Flysch Complex were part of the same NW African paleomargin. These patterns include scarce Paleozoic zircon grains that show influence from the Sehoul Block. Neoproterozoic and Paleoproterozoic grains are abundant with a dominant Ediacaran zircon population at ca. 590 Ma, which could have been sourced from the Variscan Moroccan Mesetas, the northern components of the West African Craton, or from Triassic sediments from the Central High Atlas and Argana basins. Mesoproterozoic zircon ages between 1.1 and 1.6 Ga were also observed (15% in the combined age spectra), the nearest sources for these being in the central part of the West African Craton. Transport of the Mesoproterozoic grains to the NW African paleomargin requires northward-directed fluvial systems parallel to the Central Atlantic continental margin of Africa. In contrast, samples from the Internal Rif or Alborán Domain are different to those from the External Rif and Maghrebian Flysch Complex, especially in the scarcity of Mesoproterozoic zircons, suggesting that the Alborán Domain was not a source area for zircons found in the NW African paleomargin.  相似文献   

Circular features in the Trans-Mexican Volcanic Belt     

《Journal of Volcanology and Geothermal Research》2001,107(4):265-274

One hundred and ninety-one circular or elliptical features have been located on Landsat imagery of the Trans-Mexican Volcanic Belt (TMVB). The origin of most of these features is unknown. Nine have been recognized as collapse calderas (clearly visible on Landsat imagery) and studied in detail, while an equally small number have been tentatively identified as such but not thoroughly investigated. On the basis of the identification of at least five of the nine calderas through their detection on Landsat images, it is proposed that the present inventory is a reliable base to extend the census of the TMVB confirmed calderas, now clearly too small for a population of roughly 8000 volcanic centers, many of which emitted large volumes of felsic pyroclastic products.  相似文献   

Improvements to source protection for private water supplies in Scotland,UK     

《Water Policy》2001,3(4):273-281

Private water supplies are defined as any water supply which is not provided by a statutory water undertaker and in which the responsibility for its maintenance lies with the owner or person who uses the supply. In Scotland around 60,000 people rely on such supplies from which they will be receiving water subject to either limited or no statutory requirement for quality sampling. Further, while 60,000 is the resident population, a large number of people attending campsites, hotels, guesthouses or using food outlets will be exposed to private supplies for transitory periods of time. Of greatest concern is the threat of microbial contamination resulting in an increased threat to public health. In an effort to improve the microbiological quality of the drinking water from private supplies a microbiological risk assessment protocol was developed to enhance the source protection of such supplies. This paper details the development of this protocol.  相似文献