Modeling and imaging land-cover influences on air temperature in and near Baltimore,MD     

Gordon M. Heisler  Alexis Ellis  David J. Nowak  Ian Yesilonis 《Theoretical and Applied Climatology》2016,124(1-2):497-515

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Present-day and future Antarctic ice sheet climate and surface mass balance in the Community Earth System Model     

Jan T. M. Lenaerts  Miren Vizcaino  Jeremy Fyke  Leo van Kampenhout  Michiel R. van den Broeke 《Climate Dynamics》2016,47(5-6):1367-1381

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Cenozoic evolution of the central Myanmar drainage system: insights from sediment provenance in the Minbu Sub‐Basin          下载免费PDF全文

Alexis Licht  Laurie Reisberg  Christian France‐Lanord  Aung Naing Soe  Jean‐Jacques Jaeger 《Basin Research》2016,28(2):237-251

Located at the southern edge of the eastern Himalayan syntaxis, the Central Myanmar Basin (CMB) is divided into several Tertiary sub‐basins that have been almost continuously filled since the Indo‐Asia collision. They are currently drained by the Irrawaddy River, which flows down the eastern Tibetan Plateau and the Sino‐Burman Ranges. Tracing sediment provenance from the CMB is thus critical for reconstructing the past denudation of the Himalayan‐Tibetan orogen; it is especially relevant since a popular drainage scenario involves the capture of the Tsangpo drainage system in Tibet by a precursor to the Irrawaddy River. Here, we document the provenance of sediment samples from the Minbu Sub‐Basin at the southern edge of the CMB, which is traversed by the modern stream of the Irrawaddy River. Samples ranging in age from middle Eocene to Pleistocene were investigated using Nd isotopes, trace element geochemistry and sandstone modal compositions. Our data provide no evidence of a dramatic provenance shift; however, sandstone petrography, trace element ratios and isotopic values display long‐term trends indicating a gradual decrease of the volcanic input and its replacement by a dominant supply from the Burmese basement. These trends are interpreted to reflect the progressive denudation of the Andean‐type volcanic arc that extended onto the Burmese margin, along the flank of the modern Sino‐Burman Ranges, where most of the post‐collisional deformation of central Myanmar is located. Though our results do not exclude an ephemeral or diluted contribution from a past Tsangpo‐Irrawaddy connection, sedimentation rates suggest that this hypothesis is unlikely before the development of a stable Tsangpo‐Brahmaputra River in the Miocene. These results thus suggest that the central Myanmar drainage basin has remained restricted to the Sino‐Burman Ranges since the beginning of the India‐Asia collision.  相似文献   

Geographically weighted elastic net logistic regression     

Alexis Comber  Paul Harris 《Journal of Geographical Systems》2018,20(4):317-341

This paper develops a localized approach to elastic net logistic regression, extending previous research describing a localized elastic net as an extension to a localized ridge regression or a localized lasso. All such models have the objective to capture data relationships that vary across space. Geographically weighted elastic net logistic regression is first evaluated through a simulation experiment and shown to provide a robust approach for local model selection and alleviating local collinearity, before application to two case studies: county-level voting patterns in the 2016 USA presidential election, examining the spatial structure of socio-economic factors associated with voting for Trump, and a species presence–absence data set linked to explanatory environmental and climatic factors at gridded locations covering mainland USA. The approach is compared with other logistic regressions. It improves prediction for the election case study only which exhibits much greater spatial heterogeneity in the binary response than the species case study. Model comparisons show that standard geographically weighted logistic regression over-estimated relationship non-stationarity because it fails to adequately deal with collinearity and model selection. Results are discussed in the context of predictor variable collinearity and selection and the heterogeneities that were observed. Ongoing work is investigating locally derived elastic net parameters.  相似文献   

Seismic‐stratigraphic record of a deglaciation sequence: from the marine Laflamme Gulf to Lake Saint‐Jean (late Quaternary,Québec,Canada)     

Alexis Nutz  Jean‐François Ghienne  Mathieu Schuster  Raphaël Certain  Nicolas Robin  Claude Roquin  Olivier Raynal  Frédéric Bouchette  Philippe Duringer  Pierre A. Cousineau 《Boreas: An International Journal of Quaternary Research》2014,43(2):309-329

The stratigraphy of the last deglaciation sequence is investigated in Lake Saint‐Jean (Québec Province, Canada) based on 300 km of echo‐sounder two dimensional seismic profiles. The sedimentary archive of this basin is documented from the Late Pleistocene Laurentidian ice‐front recession to the present‐day situation. Ten seismic units have been identified that reflect spatio‐temporal variations in depositional processes characterizing different periods of the Saint‐Jean basin evolution. During the postglacial marine flooding, a high deposition rate of mud settling, from proglacial glacimarine and then prodeltaic plumes in the Laflamme Gulf, produced an extensive, up to 50 m thick mud sheet draping the isostatically depressed marine basin floor. Subsequently, a closing of the water body due to glacio‐isostatic rebound occurred at 8.5 cal. ka BP, drastically modifying the hydrodynamics. Hyperpycnal flows appeared because fresh lake water replaced dense marine water. River sediments were transferred towards the deeper part of the lake into river‐related sediment drifts and confined lobes. The closing of the water body is also marked by the onset of a wind‐driven internal circulation associating coastal hydrodynamics and bottom currents with sedimentary features including shoreface deposits, sediment drifts and a prograding shelf‐type body. The fingerprints of a forced regression are well expressed by mouth‐bar systems and by the shoreface–shelf system, the latter unexpected in such a lacustrine setting. In both cases, a regressive surface of lacustrine erosion (RSLE) has been identified, separating sandy mouth‐bar from glaciomarine to prodeltaic muds, and sandy shoreface wedges from the heterolithic shelf‐type body, respectively. The Lake Saint‐Jean record is an example of a regressive succession driven by a glacio‐isostatic rebound and showing the transition from late‐glacial to post‐glacial depositional systems.  相似文献   

<Emphasis Type="Italic">In Situ</Emphasis> Signatures of Interchange Reconnection between Magnetic Clouds and Open Magnetic Fields: A Mechanism for the Erosion of Polar Coronal Holes?     

Benoit Lavraud  Mathew J. Owens  Alexis P. Rouillard 《Solar physics》2011,270(1):285-296

We outline a method to determine the direction of solar open flux transport that results from the opening of magnetic clouds (MCs) by interchange reconnection at the Sun based solely on in-situ observations. This method uses established findings about i) the locations and magnetic polarities of emerging MC footpoints, ii) the hemispheric dependence of the helicity of MCs, and iii) the occurrence of interchange reconnection at the Sun being signaled by uni-directional suprathermal electrons inside MCs. Combining those observational facts in a statistical analysis of MCs during solar cycle 23 (period 1995 – 2007), we show that the time of disappearance of the northern polar coronal hole (1998 – 1999), permeated by an outward-pointing magnetic field, is associated with a peak in the number of MCs originating from the northern hemisphere and connected to the Sun by outward-pointing magnetic field lines. A similar peak is observed in the number of MCs originating from the southern hemisphere and connected to the Sun by inward-pointing magnetic field lines. This pattern is interpreted as the result of interchange reconnection occurring between MCs and the open field lines of nearby polar coronal holes. This reconnection process closes down polar coronal hole open field lines and transports these open field lines equatorward, thus contributing to the global coronal magnetic field reversal process. These results will be further constrainable with the rising phase of solar cycle 24.  相似文献   

Determination of physical properties of the Asteroid (41) Daphne from interferometric observations in the thermal infrared     

Alexis Matter  Marco Delbo  Nicolas Crouzet  Paolo Tanga 《Icarus》2011,215(1):47-56

We describe interferometric observations of the Asteroid (41) Daphne in the thermal infrared obtained with the Mid-Infrared Interferometric Instrument (MIDI) and the Auxiliary Telescopes (ATs) of the European Southern Observatory (ESO) Very Large Telescope Interferometer (VLTI). We derived the size and the surface thermal properties of (41) Daphne by means of a thermophysical model (TPM), which is used for the interpretation of interferometric data for the first time. From our TPM analysis, we derived a volume equivalent diameter for (41) Daphne of 189 km, using a non-convex 3-D shape model derived from optical lightcurves and adaptive optics images (B. Carry, private communication). On the other hand, when using the convex shape of Kaasalainen et al. (Kaasalainen, M., Mottola, S., Fulchignoni, M. [2002]. Icarus 159, 369-395) in our TPM analysis, the resulting volume equivalent diameter of (41) Daphne is between 194 and 209 km, depending on the surface roughness. The shape of the asteroid is used as an a priori information in our TPM analysis. No attempt is made to adjust the shape to the data. Only the size of the asteroid and its thermal parameters such as, albedo, thermal inertia and roughness are adjusted to the data. We estimated our model systematic uncertainty to be of 4% and of 7% on the determination of the asteroid volume equivalent diameter depending on whether the non-convex or the convex shape is used, respectively. In terms of thermal properties, we derived a value of the surface thermal inertia smaller than 50 J m⁻² s^−0.5 K⁻¹ and preferably in the range between 0 and ∼30 J m⁻² s^−0.5 K⁻¹. Our TPM analysis also shows that Daphne has a moderate macroscopic surface roughness.  相似文献   

Paleolakes, paleofloods, and depressions in Aurorae and Ophir Plana, Mars: Connectivity of surface and subsurface hydrological systems     

Goro Komatsu  Gaetano Di Achille  Ciprian Popa  Stefano Di Lorenzo  Jose Alexis Palmero Rodriguez 《Icarus》2009,201(2):474-491

The plains of Aurorae and Ophir in the equatorial region of Mars display geomorphic evidence indicative of extensive but generally short-lived paleohydrological processes. Elaver Vallis in Aurorae Planum south of Ganges Chasma is an outflow channel system >180 km long, and here inferred to have formed by cataclysmic spillover flooding from a paleolake(s) contained in the Morella crater basin. Ganges Cavus is an enormous 5-km-deep depression of probable collapse origin located in the Morella basin. The fluid responsible for the infilling of the Morella basin likely emerged at least partially through Ganges Cavus or its incipient depression, and it may have been supplied also from small-scale springs in the basin. Similar paleohydrological processes are inferred also in Ophir Planum. It is reasonable to assume that water, sometimes sediment-laden and/or mixed with gases, was the responsible fluid for these phenomena although some of the observed features could be explained by non-aqueous processes such as volcanism. Water emergence may have occurred as consequences of ground ice melting or breaching of cryosphere to release water from the underlying hydrosphere. Dike intrusion is considered to be an important cause of formation for the cavi and smaller depressions in Aurorae and Ophir Plana, explaining also melting of ground ice or breaching of cryosphere. Alternatively, the depressions and crater basins may have been filled by regional groundwater table rising during the period(s) when cryosphere was absent or considerably thin. The large quantities of water necessary for explaining the paleohydrological processes in Aurorae and Ophir Plana could have been derived through crustal migration from the crust of higher plains in western Ophir Planum where water existed in confined aquifers or was produced by melting of ground ice due to magmatic heating or climatic shift, or from a paleolake in Candor Chasma further west.  相似文献   

Définition de la perméabilité équivalente des massifs fracturés par des méthodes d'homogénéisationDefinition of the permeability of fractured rock masses by homogenisation methods     

Ahmad Pouya  Alexis Courtois 《Comptes Rendus Geoscience》2002,334(13):975-979

In the methods used for determination of the hydraulic behaviour at large scale of fractured rock masses, based on the simulation of flow in a fracture network, the mean flux and the mean pressure gradient in the network are not rigorously determined. A method is given for deriving these quantities, in a heterogeneous permeable block, from pressure and flux values on the boundary of the block. A block conductivity tensor is then defined, based on the condition of linear variation of the pressure on the boundary of the block. It is shown that this conductivity tensor is symmetric and positive-definite. An example of application to a model of fractured medium is given. To cite this article: A. Pouya, A. Courtois, C. R. Geoscience 334 (2002) 975–979.  相似文献   

Genesis and evolution of low-Al orthopyroxene in spinel peridotite xenoliths, Grand Canyon field, Arizona, USA     

D. Smith  J. C. Alexis Riter 《Contributions to Mineralogy and Petrology》1997,127(4):391-404

Orthopyroxene porphyroblasts zoned to interiors abnormally low in Al and Cr and containing numerous inclusions of olivine occur in some spinel peridotite xenoliths from the Colorado Plateau. Rims of these orthopyroxene grains contain 2.5–3.0 wt% Al₂O₃, consistent with equilibration in spinel peridotite at temperatures near 850 °C, but interiors contain as little as 0.20 wt% Al₂O₃ and 0.04 wt% Cr₂O₃. The Al-poor compositions are inferred to have equilibrated in chlorite peridotite, before porphyroblast growth during heating and consequent reactions that eliminated talc, tremolite, and chlorite. The distinctive orthopyroxene textures are inferred to have formed during reaction of talc and olivine. Rare intergrowths of orthopyroxene plus diopside are attributed to olivine-tremolite reaction. Al and Cr have gradients at grain rims that appear little modified by diffusion, but divalent elements are almost homogeneous throughout the porphyroblasts. Judging from the relative gradients, diffusion of Ca was at least 100 times faster than that of Al and Cr at the temperatures near and below 850 °C. Diffusion of Al and Cr was most effective along subgrain boundaries, and along these boundaries it appears to have been at least ten times faster than within the lattice: diffusion along such boundaries may be a dominant mechanism for re-equilibration of orthopyroxene at low mantle temperatures. Orthopyroxene with similar low Al and Cr occurs in chlorite peridotite xenoliths from the Navajo field, 300 km east of the Grand Canyon localities, and in spinel peridotite xenoliths from the Sierra Nevada, 500 km west across the extended Basin and Range province. Chlorite peridotite may therefore have been a significant minor component in much of the mantle lithosphere of western North America, although evidence for it would be erased at the higher temperatures recorded by xenoliths from the Basin and Range. Chemical changes during hydration may have been important in the evolution of these mantle volumes, and the case for addition of Sr is particularly strong. Dehydration reactions during heating could have influenced patterns of extension and crustal magmatism. Received: 1 July 1996 / Accepted: 2 December 1996  相似文献