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191.
Gravity field and interior of Rhea from Cassini data analysis 总被引:1,自引:0,他引:1
Luciano Iess Nicole J. Rappaport Jonathan Lunine Sami W. Asmar Francesco Zingoni 《Icarus》2007,190(2):585-593
The Cassini spacecraft encountered Rhea on November 26, 2005. Analysis of the Doppler data acquired at and around closest approach yields the mass of Rhea and the quadrupole moments of its gravity field with unprecedented accuracy. We obtained which corresponds to a density of . Our results for J2 and C22 are (7.947±0.892)×10−4 and (2.3526±0.0476)×10−4, respectively. These values are consistent with hydrostatic equilibrium. From the value of C22, we infer the non-dimensional moment of inertia C/MR2=0.3721±0.0036. Our models of Rhea's interior based on the gravity data favor an almost undifferentiated satellite. A discontinuity between a core and a mantle is possible but not required by the data. Models with a constant silicate mass fraction throughout the body cannot account for the determined quadrupole coefficients. The data exclude fully differentiated models in which the core would be composed of unhydrated silicates and the mantle would be composed of pure ice. If the mantle contains 10% in mass of silicates, the core extends to 630 km in radius and has a silicate mass fraction of 40%. A continuous model in which the silicates are more concentrated toward the center of the body than in the outer layers is allowed by the gravity data but excluded by thermal evolution considerations. The one model that fits the gravity data and is self-consistent when energy transport and ice melting are qualitatively considered is an “almost undifferentiated” Rhea, in which a very large uniform core is surrounded by a relatively thin ice shell containing no rock at all. 相似文献
192.
Sediment cores from two bedrock-dammed lakes in North Fork Big Pine Creek, Sierra Nevada, California, preserve the most detailed and complete record of Holocene glaciation yet recovered in the region. The lakes are fed by outwash from the Palisade Glacier, the largest (~1.3 km2) and presumably longest-lived glacier in the range, and capture essentially all of the rock flour it produces. Distinct late-Holocene (Matthes) and late-Pleistocene (Recess Peak) moraines lie between the modern glacier and the lakes. The lakes have therefore received continuous sedimentation from the basin since the retreat of the Tioga glacier (Last Glacial Maximum) and capture rock flour related to all post-LGM advances. A total of eight long cores (up to 5.5 m sediment depth) and one short surface sediment short core preserve a coherent record of fluctuating rock flour flux to the lakes through the Holocene. Age constraints on rock flour spikes in First and Second lakes based on 31 14C-dated macrofossils indicate Holocene glaciation began ~3200 cal yr B P, followed by a possible glacier maximum at ~2800 cal yr B P and four distinct glacier maxima at ~2200, ~1600, ~700 and ~250-170 cal yr. B.P., the most recent maximum being the largest.Reconstruction of the equilibrium-line altitudes (ELA) associated with each distinct advance recorded in the moraines (Recess Peak, Matthes, and modern) indicates ELA depressions (relative to modern) of ~250 m and 90 m for Recess Peak and Matthes advances, respectively. These differences represent decreases in summer temperatures of 1.7–2.8 °C (Recess Peak) and 0.2–2° (Matthes), and increases in winter precipitation of 22-34 cm snow water equivalent (s.w.e.) (Recess Peak) and 3-26 cm s.w.e. (Matthes) compared to modern conditions. Although small, these changes are significant and similar to those noted in the Cascade Range to the north, and represent a significant departure from historical climate trends in the region. 相似文献
193.
Nicole C. Lautze Thomas W. Sisson Margaret T. Mangan Timothy L. Grove 《Contributions to Mineralogy and Petrology》2011,161(2):331-347
Diffusive coarsening (Ostwald ripening) of H2O and H2O-CO2 bubbles in rhyolite and basaltic andesite melts was studied with elevated temperature–pressure experiments to investigate
the rates and time spans over which vapor bubbles may enlarge and attain sufficient buoyancy to segregate in magmatic systems.
Bubble growth and segregation are also considered in terms of classical steady-state and transient (non-steady-state) ripening
theory. Experimental results are consistent with diffusive coarsening as the dominant mechanism of bubble growth. Ripening
is faster in experiments saturated with pure H2O than in those with a CO2-rich mixed vapor probably due to faster diffusion of H2O than CO2 through the melt. None of the experimental series followed the time1/3 increase in mean bubble radius and time−1 decrease in bubble number density predicted by classical steady-state ripening theory. Instead, products are interpreted
as resulting from transient regime ripening. Application of transient regime theory suggests that bubbly magmas may require
from days to 100 years to reach steady-state ripening conditions. Experimental results, as well as theory for steady-state
ripening of bubbles that are immobile or undergoing buoyant ascent, indicate that diffusive coarsening efficiently eliminates
micron-sized bubbles and would produce mm-sized bubbles in 102–104 years in crustal magma bodies. Once bubbles attain mm-sizes, their calculated ascent rates are sufficient that they could
transit multiple kilometers over hundreds to thousands of years through mafic and silicic melt, respectively. These results
show that diffusive coarsening can facilitate transfer of volatiles through, and from, magmatic systems by creating bubbles
sufficiently large for rapid ascent. 相似文献
194.
The relationships between meteorological conditions (temperature, wind-speed and direction, relative humidity, surface-inversion depth and strength, and stability) and PM2.5 concentrations in Fairbanks, Alaska were investigated using ten years of observational data. The results show that during wintertime (November through February) PM2.5 concentrations exceeding the 24 h National Air Quality Standard (35 μg/m3) occurred under calm wind, extremely low temperature (≤20 °C) and moisture (water-vapor pressure < 2 hPa) multiday surface-inversion conditions that trap the pollutants in the breathing level and inhibit transport of polluted air out of Fairbanks. PM2.5 concentrations tend to be higher under stable than other conditions, but are not sensitive to the degree of stability. The presence of a surface inversion and calm wind are necessary, but in combination with low temperatures and humidity, the conditions are sufficient for high PM2.5 concentrations. The low temperatures are required because they lead to increased emission rates from domestic heating and power production. During multiday inversions with temperatures above ? 20 °C, high relative humidity (> 75%) partly caused by water-vapor emission reduces PM2.5 concentrations. 相似文献
195.
Helsen Samuel van Lipzig Nicole P. M. Demuzere Matthias Vanden Broucke Sam Caluwaerts Steven De Cruz Lesley De Troch Rozemien Hamdi Rafiq Termonia Piet Van Schaeybroeck Bert Wouters Hendrik 《Climate Dynamics》2020,54(3):1267-1280
Climate Dynamics - Convection-permitting models (CPMs) have been proven successful in simulating extreme precipitation statistics. However, when such models are used to study climate change,... 相似文献
196.
Sang Hoang Nicole Meyer-Vernet Michel Moncuquet Alain Lecacheux Bent M. Pedersen 《Planetary and Space Science》1993,41(11-12)
During the Ulysses flyby of Jupiter, the spacecraft crossed the outer part of the Io plasma torus along a basically North-to-South trajectory at a Jovicentric distance of about 8RJ. The quasi-thermal noise measured by the Unified Radio and Plasma Wave (URAP) experiment is used to deduce the electron density and temperature along the trajectory. The density is deduced from the upper hybrid frequency line and the temperature from the spin modulation of Bernstein waves. These results are used to build a simplified Gaussian model of the torus. The density profile is roughly symmetric with respect to the centrifugal equator, with a scale height of about 0.9RJ. The density at equator crossing is twice as large as that expected from the Divine-Garrett Voyager-based model at the same radial distance. The density scale height is lower than that found by Voyager 1; it is consistent with an ion temperature of about 5 × 105K, assuming an effective mass of about 20 proton masses. The fitting of the pressure distribution, symmetric with respect to the centrifugal equator, yields a cold electron temperature of about 1.4 × 105K at the equator, which is of the same order of magnitude as found by Voyager 1. 相似文献
197.
Jan S. Laberg Kiichiro Kawamura Hilde Amundsen Nicole Baeten Matthias Forwick Tom A. Rydningen Tore O. Vorren 《Geo-Marine Letters》2014,34(1):51-58
Swath-bathymetry data and 2D multichannel seismics reveal for the first time an up to ~60 km wide amphitheater-shaped slide scar on the eastern flank of the Jan Mayen Ridge, a micro-continent in the Norwegian–Greenland Sea. The scar opens southeastward where it continues as a narrower, topographically controlled translational area. It includes secondary scars, as well as channels and escarpments. Based on the identification of secondary scars, the slide is classified as a slide complex and the total volume of missing sediments was estimated at ~60 km3. From the overall shape of the scar, the upslope widening from a bottleneck- or channel-like bypass-area, the failure is inferred to have had a retrogressive development. The absence of ridges, slabs and sediment blocks indicates that the failed sediments have been evacuated entirely. The smaller channels were formed from single or repetitive smaller flows post-dating the large failure events. 相似文献
198.
Dustin R. L. Dahn James A. Braid J. Brendan Murphy Cecilio Quesada Nicole Dupuis Christopher R. M. McFarlane 《International Journal of Earth Sciences》2014,103(5):1415-1431
The Peramora Mélange is part of an accretionary complex between the South Portuguese Zone (a fragment of Laurussia) and the Ossa Morena Zone (para-autochthonous Gondwana) and is an expression of the Pangean suture zone in southwestern Iberia. The suture zone is characterized by fault-bounded units of metasedimentary rocks, mélanges, and mafic complexes. Detailed geologic mapping of the Peramora Mélange reveals a complex pattern of imbricated schists and mafic block-in-matrix mélanges. Geochemical signatures of the Pulo do Lobo schist (PDL) are consistent with derivation from both mafic and continental sources. The mafic block-in-matrix mélange displays normal mid-ocean ridge basalt (NMORB) geochemical signature, juvenile Sm–Nd isotopic compositions, and a range of zircon ages similar to those observed in the PDL, suggesting a sedimentary component. Taken together, these data suggest a complex tectonic history characterized by erosion of a NMORB source, mélange formation, and imbrication during underplating occurring during the final stages of continent–continent collision. 相似文献
199.
Multi-method assessment of connectivity between surface water and shallow groundwater: the case of Limarí River basin,north-central Chile 总被引:2,自引:1,他引:1
Ricardo Oyarzún Felisa Barrera Pamela Salazar Hugo Maturana Jorge Oyarzún Evelyn Aguirre Pablo Alvarez Hervé Jourde Nicole Kretschmer 《Hydrogeology Journal》2014,22(8):1857-1873
A study that tests the applicability and consistency of independent but complementary approaches in the assessment of interactions between surface water and shallow groundwater within a water-stressed basin is described. The mostly agricultural Limarí basin in arid north-central Chile was chosen as a suitable case study. The analyses involved: (1) a connectivity index method, (2) hydrochemistry, and (3) water isotopic geochemistry. Chemical and isotopic data were obtained from two sampling campaigns conducted in April (fall) and December (summer) of 2011 in 22 sampling locations, which included surface water and groundwater. The results obtained by each of the methodologies were mutually consistent and indicate high connectivity conditions. Additionally, the relative contribution by different sources was assessed through end-member mixing analysis, and for reaches of the river that showed gaining conditions, the contribution of groundwater inflow to stream discharge was estimated. It is suggested that this multi-method approach is useful for the characterization of surface-water–groundwater interactions, since it at least represents a suitable starting point for obtaining basic information on these relationships. Thus, it may become the base for further studies in arid and semi-arid basins facing water management challenges. 相似文献
200.
Gernot Arp Claudia Kolepka Klaus Simon Volker Karius Nicole Nolte Bent T. Hansen 《Meteoritics & planetary science》2013,48(12):2491-2516
The extent of impact‐generated hydrothermal activity in the 24 km sized Ries impact structure has been controversially discussed. To date, mineralogical and isotopic investigations point to a restriction of hydrothermal activity to the impact‐melt bearing breccias, specifically the crater‐fill suevite. Here, we present new petrographic, geochemical, and isotopic data of postimpact carbonate deposits, which indicate a hydrothermal activity more extended than previously assumed. Specifically, carbonates of the Erbisberg, a spring mound located upon the inner crystalline ring of the crater, show travertine facies types not seen in any of the previously investigated sublacustrine soda lake spring mounds of the Ries basin. In particular, the streamer carbonates, which result from the encrustation of microbial filaments in subaerial spring effluents between 60 and 70 °C, are characteristic of a hydrothermal origin. While much of the primary geochemical and isotopic signatures in the mound carbonates have been obliterated by diagenesis, a postimpact calcite vein from brecciated gneiss of the subsurface crater floor revealed a flat rare earth element pattern with a clear positive Eu anomaly, indicating a hydrothermal fluid convection in the crater basement. Finally, the strontium isotope stratigraphic correlation of the travertine mound with the crater basin succession suggests a hydrothermal activity for about 250,000 yr after the impact, which would be much longer than previously assumed. 相似文献