The dynamics of thin shells with variable viscosity and the origin of toroidal flow in the mantle   总被引：4，自引：0，他引：4  

Neil M. Ribe 《Geophysical Journal International》1992,110(3):537-552

  相似文献   

Paleomagnetism of Late Cretaceous Poços de Caldas alkaline complex,Southern Brazil     

Neil D. Opdyke  William D. MacDonald 《Earth and Planetary Science Letters》1973,18(1):37-44

The paleomagnetism of the Late Cretaceous Poços de Caldas alkaline complex (46.6°W, 21.9°S) was investigated through 42 oriented cores from seven sites. Six sites, reversed relative to the present magnetic field of the Earth, yield a pole at 127°W, 82°S (dp = 8°,dm = 13°). This pole is located close to other Late Cretaceous poles for South America obtained by Creer [1] from untreated paleomagnetic samples. The results are significantly different from those for the nearby Early Cretaceous Serra Geral basalt but close to the Triassic pole for South America. The polar wandering path for South America for the Mesozoic seems to be more complicated than anticipated. The available paleomagnetic information may not yet be precise enough to determine the time of opening of the Atlantic.  相似文献   

Discussion of paper by Mörner and Lanser concerning the paleomagnetism of deep-sea core A179-15     

Neil D. Opdyke 《Earth and Planetary Science Letters》1976,29(1):238-239

  相似文献   

A Saturnian gas ring and the recycling of Titan's atmosphere     

Thomas R. McDonough  Neil M. Brice 《Icarus》1973,20(2):136-145

Atoms which escape Titan's atmosphere are unlikely to possess escape velocity from Saturn, and can orbit the planet until lost by ionization or collision with Titan. It is predicted that a toroidal ring of between ～1 and ～10³ atoms or molecules cm^?3 exists around Saturn at a distance of about 10 times the radius of the visible rings. This torus may be detectable from Earth-orbit and detection of nondetection of it may provide some information about the presence or absence of a Saturnian magnetic field, and the exospheric temperature and atmospheric escape rate of Titan. It is estimated that, if Titan has a large exosphere, ～97% or more of the escaping atoms can be recaptured by Titan, thereby decreasing the effective net atmospheric loss rate by up to two orders of magnitude. With such a reduction in atmospheric loss rates, it becomes more plausible to suggest that satellites previously thought too small to retain an atmosphere may have one. It is suggested that Saturn be examined by Lyman-α and other observations to search for the gaseous torus of Titan. If successful, these could then be extended to other satellites.The effect of a hypothetical Saturnian magnetosphere on the atmosphere of Titan is investigated. It is shown that, if Saturn has a magnetic field comparable to Jupiter's (～10 G at the planetary surface), the magnetospheric plasma can supply Titan with hydrogen at a rate comparable to the loss rates in some of the models of Trafton (1972) and Sagan (1973). A major part of the Saturnian ionospheric escape flux (～ 10²⁷ photoelectrons sec^?1) could perhaps be captured by Titan. At the upper limit, this rate of hydrogen input to the satellite could total ～0.1 atm pressure over the lifetime of the solar system, an amount comparable to estimates of the present atmospheric pressure of Titan.  相似文献   

Mapping of Ozone and Water in the Atmosphere of Mars near the 1997 Aphelion     

Robert E. NovakMichael J. Mumma  Michael A. DiSanti  Neil Dello Russo  Karen Magee-Sauer 《Icarus》2002,158(1):14-23

We present absolute abundances and latitudinal variations of ozone and water in the atmosphere of Mars during its late northern spring (L_s=67.3°) shortly before aphelion. Long-slit maps of the a¹Δ_g state of molecular oxygen (O₂) and HDO, an isotopic form of water, were acquired on UT January 21.6 1997 using a high-resolution infrared spectrometer (CSHELL) at the NASA Infrared Telescope Facility. O₂(a¹Δ_g) is produced by ozone photolysis, and the ensuing dayglow emission at 1.27 μm is used as a tracer for ozone. Retrieved vertical column densities for ozone above ∼20 km ranged between 1.5 and 2.8 μm-atm at mid- to low latitudes (30°S-60°N) and decreased outside that region. A significant decrease in ozone density is seen near 30°N (close to the subsolar latitude of 23.5°N). The rotational temperatures retrieved from O₂(a-X) emissions show a mean of 172±2.5 K, confirming that the sensed ozone lies in the middle atmosphere (∼24 km). The ν₁ fundamental band of HDO near 3.67 μm was used as a proxy for H₂O. The retrieved vertical column abundance of water varies from 3 precipitable microns (pr-μm) at ∼30°S to 24 pr-μm at ∼60°N. We compare these results with current photochemical models and with measurements obtained by other methods.  相似文献   

The outer scale of solar-wind turbulence from GALILEO coronal-sounding data     

A. I. Efimov  I. V. Chashei  L. N. Samoznaev  V. E. Andreev  M. K. Bird  P. Edenhofer  D. Plettemeier  R. Wohlmuth 《Astronomy Reports》2002,46(7):579-590

Radio sounding experiments on of the solar plasma were carried out by the GALILEO spacecraft using S-band (2295 MHz) signals in 1995–1996 a period of minimum solar activity. Equatorial regions at heliocentric distances of 7–80 solar radii were studied. The frequency of the received signal was detected by three ground stations. By carrying out continuous observations of unprecedented duration and processing the data using spectral and correlation methods, we have obtained reliable information on large-scale inhomogeneities of the solar-wind density for the first time. The outer turbulence scale increases with heliocentric distance, the dependence being close to linear. We estimate the outer turbulence scale and analyze its dependence on distance from the Sun and local plasma parameters for a model in which the outer scale is formed due to competition between the linear amplification of Alfven waves in the irregular, moving solar-wind plasma and the nonlinear transfer of turbulent energy to higher frequencies. A comparison of predictions for various specific cases of this model with the observational data suggests that the main nonlinear processes responsible for the formation of the inertial range of the spectrum on the investigated scales are three-wave decay processes involving Alfven and magnetoacoustic waves.  相似文献   

Anisotropy and velocity of small-scale irregularities in the region of solar-wind acceleration     

I. V. Chashei  A. I. Efimov  V. K. Rudash  M. K. Bird 《Astronomy Reports》2000,44(9):634-640

  相似文献   

Arsenic and presumed resistate trace element geochemistry of the Lincolnshire (UK) sedimentary ironstones,as revealed by a regional geochemical survey using soil,water and stream sediment sampling     

Neil Breward 《Applied Geochemistry》2007

A regional geochemical survey using soils, stream sediment and stream water sampling revealed multi-element geochemical anomalies, though of low environmental mobility, associated with Mesozoic sedimentary ironstones in Lincolnshire, UK. The most prominent of these anomalies were of As and V in soils and sediments, but elevated levels of elements such as Cr, La, Ce and Th were also observed. These were initially thought to be part of a residual resistate element or heavy-mineral suite, but careful examination suggests that these too may be primarily associated with the process of Fe oxide precipitation during the initial formation of the ironstones.  相似文献   

Interpreting the Ca isotope record of marine biogenic carbonates     

Neil G. Sime  Edward T. Tipper  Albert Galy 《Geochimica et cosmochimica acta》2007,71(16):3979-3989

An 18 million year record of the Ca isotopic composition (δ^44/42Ca) of planktonic foraminiferans from ODP site 925, in the Atlantic, on the Ceara Rise, provides the opportunity for critical analysis of Ca isotope-based reconstructions of the Ca cycle. δ^44/42Ca in this record averages +0.37 ± 0.05 (1σ SD) and ranges from +0.21‰ to +0.52‰. The record is a good match to previously published Neogene Ca isotope records based on foraminiferans, but is not similar to the record based on bulk carbonates, which has values that are as much as 0.25‰ lower. Bulk carbonate and planktonic foraminiferans from core tops differ slightly in their δ^44/42Ca (i.e., by 0.06 ± 0.06‰ (n = 5)), while the difference between bulk carbonate and foraminiferan values further back in time is markedly larger, leaving open the question of the cause of the difference. Modeling the global Ca cycle from downcore variations in δ^44/42Ca by assuming fixed values for the isotopic composition of weathering inputs (δ^44/42Ca_w) and for isotope fractionation associated with the production of carbonate sediments (Δ_sed) results in unrealistically large variations in the total mass of Ca²⁺ in the oceans over the Neogene. Alternatively, variations of ±0.05‰ in the Ca isotope composition of weathering inputs or in the extent of fractionation of Ca isotopes during calcareous sediment formation could entirely account for variations in the Ca isotopic composition of marine carbonates. Ca isotope fractionation during continental weathering, such as has been recently observed, could easily result in variations in δ^44/42Ca_w of a few tenths of permil. Likewise a difference in the fractionation factors associated with aragonite versus calcite formation could drive shifts in Δ_sed of tenths of permil with shifts in the relative output of calcite and aragonite from the ocean. Until better constraints on variations in δ^44/42Ca_w and Δ_sed have been established, modeling the Ca²⁺ content of seawater from Ca isotope curves should be approached cautiously.  相似文献   

Does variable channel morphology lead to dynamic salmon habitat?     

David A. Reid  Marwan A. Hassan  Stephen Bird  Robin Pike  Peter Tschaplinski 《地球表面变化过程与地形》2020,45(2):295-311

Stream channel morphology forms the template upon which hydraulic aspects of aquatic habitat are created, yet spatial and temporal variability in habitat imposed by changing morphology is not well understood. This paper presents a conceptual model linking sediment supply patterns to spatial and temporal variability in channel form and aquatic habitat. To evaluate this model, change over time in three habitat variables is quantified using a 2D hydrodynamic modeling approach. A 45-year record of topographic data from Carnation Creek, a catchment in coastal British Columbia, is used for the flow modeling. Using the Nays2DH modeling platform, water depths and velocities are simulated in eight channel segments located at different positions relative to locations of historical colluvial input using seven flow levels ranging from 3% to 400% of mean annual discharge (0.02 to 3.31 m s ). Results indicate that habitat availability changes through time as a result of sediment supply-driven changes to channel morphology and wood loads, but patterns in habitat vary as a function of dominant channel segment morphology. Spatial and temporal variability in morphology also influences the relationship between habitat availability and river discharge, leading to non-stationary habitat-discharge rating curves. When habitat areas are predicted by applying these curves to daily flow series spanning annual dry seasons, over 50% of the variance in cumulative seasonal habitat area can be explained by year-to-year changes in channel morphology and wood loading, indicating that changing morphology is an important factor for driving temporal habitat variability. This variance is related to the morphological variability of a channel segment, which in turn is associated with the segment position relative to zones of colluvial input. Collectively, these results suggest that variability in habitat is impacted by channel morphology, and can be evaluated partly on the basis of a channel's sediment supply regime. © 2019 John Wiley & Sons, Ltd.  相似文献