Modeling of the magnetosphere of Mercury at the time of the first MESSENGER flyby     

Mehdi Benna  Brian J. Anderson  Scott A. Boardsen  Robert E. Gold  Rosemary M. Killen  Stamatios M. Krimigis  Ralph L. McNutt Jr.  William E. McClintock  James A. Slavin  Thomas H. Zurbuchen 《Icarus》2010,209(1):3-10

The MESSENGER spacecraft flyby of Mercury on 14 January 2008 provided a new opportunity to study the intrinsic magnetic field of the innermost planet and its interaction with the solar wind. The model presented in this paper is based on the solution of the three-dimensional, bi-fluid equations for solar wind protons and electrons in the absence of mass loading. In this study we provide new estimates of Mercury’s intrinsic magnetic field and the solar wind conditions that prevailed at the time of the flyby. We show that the location of the boundary layers and the strength of the magnetic field along the spacecraft trajectory can be reproduced with a solar wind ram pressure P_sw = 6.8 nPa and a planetary magnetic dipole having a magnitude of 210 R_M³ − nT and an offset of 0.18 R_M to the north of the equator, where R_M is Mercury’s radius. Analysis of the plasma flow reveals the existence of a stable drift belt around the planet; such a belt can account for the locations of diamagnetic decreases observed by the MESSENGER Magnetometer. Moreover, we determine that the ion impact rate at the northern cusp was four times higher than at the southern cusp, a result that provides a possible explanation for the observed north-south asymmetry in exospheric sodium in the neutral tail.  相似文献   

Impact of climate change on diffuse pollutant fluxes at the watershed scale          下载免费PDF全文

Mehdi Ahmadi  Rosemary Records  Mazdak Arabi 《水文研究》2014,28(4):1962-1972

This study aims to assess watershed‐scale impacts of changing climate on sediment, phosphorus, nitrogen and pesticide (atrazine) fluxes over the 21st century at the watershed scale. In particular, changes in dissolved and particulate forms of water quality constituents in response to climate change are investigated. The hydrologic model Soil and Water Assessment Tool was calibrated and evaluated in a primarily agricultural watershed in the Midwestern United States to simulate hydrologic and water quality processes on a daily basis over the 2015–2099 time horizon. The model was then driven with 112 distinct statistically downscaled climate projections representing Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios (IPCC SRES) low, moderate and high greenhouse gas emission scenarios. Projected hydrologic and water quality responses were categorized according to the three IPCC SRES emission scenarios for summarizing and synthesizing results over early‐century (2015–2034), mid‐century (2045–2064) and late‐century (2080–2099) assessment. Results revealed clear warming trends in the study area, whereas small increases in precipitation were predicted. Streamflow, sediment and total nutrient loads did not differ noticeably between assessment periods. However, the proportion of dissolved to total nutrients increased significantly from early‐century to late‐century periods. With the exception of total atrazine in the mid‐century period, predicted pollutant loads for a given assessment period did not differ between emission pathways for a given assessment period. Changes in pollutant fluxes showed pronounced monthly variability. The projected increase in readily available forms of nutrients has important implications for the ecological health of water systems and management of drinking water supplies. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

The Millennium Galaxy Catalogue: star counts and the structure of the Galactic stellar halo     

D. J. Lemon  Rosemary F. G. Wyse †  J. Liske  S. P. Driver  Keith Horne 《Monthly notices of the Royal Astronomical Society》2004,347(4):1043-1054

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Editorial     

Bernard Barnier  Yves Du Penhoat  Lee-Lueng Fu  Rosemary Morrow  Jacques Verron  Phil Woodworth 《Ocean Dynamics》2006,56(5-6):377-378

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A multi-station magnetotelluric study in southern Scotland – I. Fieldwork, data analysis and results     

Man G. Jones  Rosemary Hutton 《Geophysical Journal International》1979,56(2):329-349

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The AVA (amplitude-versus-angle) signature of small-scale reflector topography     

Rosemary K. Quinn  Roger A. Clark †  Jürgen W. Neuberg ‡ 《Geophysical Prospecting》2001,49(1):59-70

Routine amplitude‐versus‐offset or amplitude‐versus‐angle (AVA) analysis is founded on the predicted reflectivity of a planar boundary between isotropic homogeneous half‐spaces, yet many real boundaries of interest to hydrocarbon exploration may violate these assumptions. Here, we evaluate consequences of boundary roughness, i.e. small‐scale, sub‐resolution topography, on the reflecting boundary, to find whether sub‐resolution topography can deceive routine AVA analysis and produce misleading hydrocarbon indicators. We use noise‐free synthetic CMP and stacked‐section seismograms, generated with a Kirchhoff‐integral method, for offsets up to 4000 m. The reflecting boundary was at 2000 m depth below a single overburden layer, and comprised isolated mounds or channels (sinusoidal cross‐section, 5–40 m high and 100–750 m wide), and more complex roughness (simulated with seven 1.5–2 km long bathymetric profiles across modern‐day river‐beds, with dune and bar features up to approximately 20 m or 20 ms TWT vertical relief, and 10–100 m or more lateral extent). Flat‐boundary responses were taken as the ‘reference’ against which to compare waveforms and amplitudes through semblance analysis, AVA intercept A and slope B cross‐plots, and inferred Poisson's ratios. Physical properties of the media were based on shales and brine‐ or oil‐sands from an offshore UK oilfield. For the CMP centred on the topographic feature, isolated mounds and channels produced correlated excursions of A and B from the flat‐boundary response (by approximately 35–200%), simulating the familiar ‘background trend’ but sometimes oblique to it. Inferred Poisson's ratios were around 0.3, but for some channels often fell as low as 0.2, potentially interpretable as gas sand. For complex boundary topographies on a shale/brine‐sand model, AVA parameters were extracted for 29 CMPs, 100 m apart along each of seven profiles. On a cross‐plot, they spanned the flat‐boundary response on a linear trend B = (0.01 ± 0.02) – (1.72 ± 0.09)A, similar to reported real data and a realistic ‘mudrock trend’ but with outliers both above and below it that could be interpreted as ‘real’ weak anomalies. Poisson's ratios were 0.30 ± 0.01, between the expected values for brine‐ and oil‐sand. This suggests that boundary roughness may contribute to observed trends on cross‐plots and possibly small, but potentially laterally extensive, false AVA anomalies may also be induced.  相似文献   

Temporal variation of isotope and rare earth element abundances in volcanic rocks from Guam: implications for the evolution of the Mariana Arc   总被引：2，自引：0，他引：2  

Rosemary Hickey-Vargas  Mark K. Reagan 《Contributions to Mineralogy and Petrology》1987,97(4):497-508

Volcanic rocks exposed on Guam were erupted during the Late Middle Eocene (Facpi Fm.), Late Eocene-Oligocene (Alutom Fm.) and Miocene (Umatac Fm.). Four magma series are recognized: the boninite series (44 m.y.b.p.), the tholeiite and calc-alkaline series, which were erupted along with boninite series lavas at 32–36 m.y.b.p. and high-K lavas of the Umatac Fm. (14 m.y.b.p.). Isotope and and rare earth element (REE) characteristics of the four magma series are distinct. Boninite series lavas have U-shaped REE patterns, relatively low ¹⁴³Nd/¹⁴⁴Nd (0.51294–0.51298), and high ²⁰⁶Pb/²⁰⁴Pb (19.0–19.2). Tholeiite series lavas are LREE (light REE) depleted, and have high ¹⁴³Nd/¹⁴⁴Nd (0.51304–0.51306) and low ²⁰⁶Pb/²⁰⁴Pb (18.4–18.5). Calc-alkaline series lavas have Sr, Nd and Pb isotope ratios similar to tholeiite series lavas, but flat to U-shaped REE patterns. Umatac Fm. lavas are strongly LREE-enriched, and have higher ⁸⁷Sr/ ⁸⁶Sr (0.70375–0.70380) and ²⁰⁷Pb/²⁰⁴Pb relative to ²⁰⁶Pb/ ²⁰⁴Pb than Facpi and Alutom Fm. lavas. Boninite and tholeiite series magmas, erupted in the position of the Palau-Kyushu Ridge, were probably derived from distinct mantle sources having OIB and N-MORB-like isotopic characteristics, together with fluids derived from subducted Pacific plate basalt. Calc-alkaline series lavas were most likely derived from the tholeiite series by extensive crystal fractionation, wallrock contamination and magma mixing. Lavas of the Umatac Fm., erupted in the position of the West Mariana Ridge, may include up to 2–3% subducted sediment, similar to some active Mariana arc lavas.  相似文献   

The subsidence history of Conoco well 15/30-1, central North Sea     

Rosemary J. Wood 《Earth and Planetary Science Letters》1981,54(2):306-312

The depth of deposition of the sediments from North Sea well Conoco 15/30-1 is determined using faunal and sedimentary evidence. The effects of sedimentary load, corrected for compaction and variations in water depth and sea level are removed, to obtain the subsidence of the basement when covered by water only. A crustal stretching and lithospheric thinning of 25–35% (β=1.35) can account for both the initial fault-controlled subsidence and the later uniform subsidence.  相似文献   

Geochemistry and isotopes of fluids from sulphur springs, Valles Caldera, New Mexico     

Fraser Goff  Jamie Gardner  Rosemary Vidale  Robert Charles 《Journal of Volcanology and Geothermal Research》1985,23(3-4)

Detailed geochemistry supported by geologic mapping has been used to investigate Sulphur Springs, an acid-sulfate hot spring system that issues from the western flank of the resurgent dome inside Valles Caldera. The most intense activity occurs at the intersection of faults offsetting caldera-fill deposits and post-caldera rhyolites. Three geothermal wells in the area have encountered pressures <1 MPa and temperatures of 200°C at depths of 600 to 1000 m. Hot spring and fumarole fluids may discharge at boiling temperatures with pH 1.0 and SO₄ 8000 mg/l. These conditions cause argillic alterations throughout a large area.Non-condensible gases consist of roughly 99% CO₂ with minor amounts of H₂S, H₂, and CH₄. Empirical gas geothermometry suggests a deep reservoir temperature of 215 to 280°C. Comparison of ¹³C and ¹⁸O between CaCO₃ from well cuttings and CO₂ from fumarole steam indicates a fractionation temperature between 200 and 300°C by decarbonation of hydrothermally altered Paleozoic limestone and vein calcite in the reservoir rocks. Tritium concentrations obtained from steam condensed in a mudpot and deep reservoir fluids (Baca #13, 278°C) are 2.1 and 1.0 T.U. respectively, suggesting the steam originates from a reservoir whose water is mostly >50 yrs old. Deuterium contents of fumarole steam, deep reservoir fluid, and local meteoric water are practically identical even though ¹⁸O contents range through 4‰, thus, precipitation on the resurgent dome of the caldera could recharge the hydrothermal system by slow percolation. From analysis of D and ¹⁸O values between fumarol steam and deep reservoir fluid, steam reaches the surface either (1) by vaporizing relatively shallow groundwater at 200°C or (2) by means of a two-stage boiling process through an intermediate level reservoir at roughly 200°C.Although many characteristics of known vapor-dominated geothermal systems are found at Sulphur Springs, fundamental differences exist in temperature and pressure of our postulated vapor-zone. We propose that the reservoir beneath Sulphur Springs is too small or too poorly confined to sustain a “true” vapor-dominated system and that the Sulphur Springs system may be a “dying” vapor-dominated system that has practically boiled itself dry.  相似文献   

Petrogenesis of the Laguna del Maule volcanic complex,Chile (36° S)     

Frederick A. Frey  David C. Gerlach  Rosemary L. Hickey  Leopoldo Lopez-Escobar  Francisco Munizaga-Villavicencio 《Contributions to Mineralogy and Petrology》1984,88(1-2):133-149

From 33°–42° S in central-south Chile, there are numerous volcanoes which form part of the Andean magmatic arc caused by subduction of the Nazca plate beneath western South America. The <0.3 m.y. old Laguna del Maule volcanic complex at 36° S is in a transition region between volcanoes at 33°–34° S formed dominantly of hornblende-bearing andesite and volcanoes south of 37° S dominantly composed of basalt and basaltic andesite. The Laguna del Maule complex ranges in composition from basalt (0.3 m.y.) to rhyolite (post-glacial). Although there is abundant evidence for magma mixing, basalt and rhyolite have similar Sr and Nd isotopic ratios, thereby requiring that the mixing members had the same isotopic ratios (⁸⁷Sr/ ⁸⁶Sr 0.70419 and ¹⁴³Nd/¹⁴⁴Nd 0.51274). In contrast, dacitic dikes and a volcanic neck which also have evidence for magma mixing are isotopically distinct. Major and trace element abundances are consistent with a genetic relationship between the basalt and rhyolite, either by low-pressure, plagioclase-dominated, fractional crystallization or by partial melting of a plagioclase-rich assemblage. There is no evidence that the rhyolites contain more of a crustal component than the associated basic volcanics.  相似文献