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221.
The magnitude and spatial distribution of snow on sea ice are both integral components of the ocean–sea‐ice–atmosphere system. Although there exists a number of algorithms to estimate the snow water equivalent (SWE) on terrestrial surfaces, to date there is no precise method to estimate SWE on sea ice. Physical snow properties and in situ microwave radiometry at 19, 37 and 85 GHz, V and H polarization were collected for a 10‐day period over 20 first‐year sea ice sites. We present and compare the in situ physical, electrical and microwave emission properties of snow over smooth Arctic first‐year sea ice for 19 of the 20 sites sampled. Physical processes creating the observed vertical patterns in the physical and electrical properties are discussed. An algorithm is then developed from the relationship between the SWE and the brightness temperature measured at 37 GHz (55°) H polarization and the air temperature. The multiple regression between these variables is able to account for over 90% of the variability in the measured SWE. This algorithm is validated with a small in situ data set collected during the 1999 field experiment. We then compare our data against the NASA snow thickness algorithm, designed as part of the NASA Earth Enterprise Program. The results indicated a lack of agreement between the NASA algorithm and the algorithm developed here. This lack of agreement is attributed to differences in scale between the Special Sensor Microwave/Imager and surface radiometers and to differences in the Antarctic versus Arctic snow physical and electrical properties. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
222.
Himalayan magmatism and porphyry copper–molybdenum mineralization in the Yulong ore belt, East Tibet
Summary ?The NW–SE-trending Yulong porphyry Cu–Mo ore belt, situated in the Sanjiang0 area of eastern Tibet, is approximately 400 km
long and 35 to 70 km wide. Complex tectonic and magmatic processes during the Himalayan epoch have given rise to favorable
conditions for porphyry-type Cu–Mo mineralization.
Porphyry masses of the Himalayan epoch in the Yulong ore belt are distributed in groups along regional NW–SE striking tectonic
lineaments. They were emplaced mainly into Triassic and Lower Permian sedimentary-volcanic rocks. K–Ar und U–Pb isotopic datings
give an intrusion age range of 57–26 Ma. The porphyries are mainly of biotite monzogranitic and biotite syenogranitic compositions.
Geological and geochemical data indicate that the various porphyritic intrusions in the belt had a common or similar magma
source, are metaluminous to peraluminous, Nb–Y–Ba-depleted, I-type granitoids, and belong to the high-K calc-alkaline series.
Within the Yulong subvolcanic belt a number of porphyry stocks bear typical porphyry type Cu–Mo alteration and mineralization.
The most prominent porphyry Co–Mo deposits include Yulong, Malasongduo, Duoxiasongduo, Mangzong and Zhanaga, of which Yulong
is one of the largest porphyry Cu (Mo) deposits in China with approximately 8 × 106 tons of contained Cu metal. Hydrothermal alteration at Yulong developed around a biotite–monzogranitic porphyry stock that
was emplaced within Upper Triassic limestone, siltstone and mudstone. The earliest alteration was due to the effects of contact
metamorphism of the country rocks and alkali metasomatism (potassic alteration) within and around the porphyry body. The alteration
of this stage was accompanied by a small amount of disseminated and veinlet Cu–Mo sulfide mineralization. Later alteration–mineralization
zones form more or less concentric shells around the potassic zone, around which are distributed a phyllic or quartz–sericite–pyrite
zone, a silicification and argillic zone, and a propylitic zone.
Fluid inclusion data indicate that three types of fluids were involved in the alteration–mineralization processes: (1) early
high temperature (660–420 °C) and high salinity (30–51 wt% NaCl equiv) fluids responsible for the potassic alteration and
the earliest disseminated and/or veinlet Cu–Mo sulfide mineralization; (2) intermediate unmixed fluids corresponding to phyllic
alteration and most Cu–Mo sulfide mineralization, with salinities of 30–50 wt% NaCl equiv and homogenization temperatures
of 460–280 °C; and (3) late low to moderate temperature (300–160 °C) and low salinity (6–13 wt% NaCl equiv) fluids responsible
for argillic and propylitic alteration. Hydrogen and oxygen isotopic studies show that the early hydrothermal fluids are of
magmatic origin and were succeeded by increasing amounts of meteoric-derived convective waters. Sulfur isotopes also indicate
a magmatic source for the sulfur in the early sulfide mineralization, with the increasing addition of sedimentary sulfur outward
from the porphyry stock.
Received August 29, 2001; revised version accepted May 1, 2002
Published online: November 29, 2002 相似文献
223.
L. A. Nolan J. S. Dunlop R. Jimenez A. F. Heavens 《Monthly notices of the Royal Astronomical Society》2003,341(2):464-476
We explore whether the rest-frame near-ultraviolet spectral region, observable in high-redshift galaxies via optical spectroscopy, contains sufficient information to allow the degeneracy between age and metallicity to be lifted. We do this by first testing the ability of evolutionary synthesis models to reclaim the correct metallicity when fitted to the near-ultraviolet spectra of F stars of known (subsolar and supersolar) metallicity. F stars are of particular interest because the rest-frame near-ultraviolet spectra of the oldest known elliptical galaxies at z > 1 appear to be dominated by F stars near to the main-sequence turn-off.
We find that, in the case of the F stars, where the Hubble Space Telescope ultraviolet spectra have a high signal-to-noise ratio, fitting models in which the metallicity is allowed to vary as a free parameter is rather successful at deriving the correct metallicity. As a result, the estimated turn-off ages of these stars yielded by model-fitting are well constrained. Encouraged by this we have fitted these same variable-metallicity models to the deep, optical spectra of the z ≃ 1.5 mJy radio galaxies 53W091 and 53W069 obtained with the Keck telescope. While the age and metallicity are not so easily constrained for these galaxies, we find that even when metallicity is allowed as a free parameter, the best estimates of their ages are still ≥3 Gyr, with ages younger than 2 Gyr now strongly excluded. Furthermore, we find that a search of the entire parameter space of metallicity and star formation history using MOPED leads to the same conclusion. Our results therefore continue to argue strongly against an Einstein–de Sitter universe, and favour a Λ-dominated universe in which star formation in at least these particular elliptical galaxies was completed somewhere in the redshift range z = 3–5 . 相似文献
We find that, in the case of the F stars, where the Hubble Space Telescope ultraviolet spectra have a high signal-to-noise ratio, fitting models in which the metallicity is allowed to vary as a free parameter is rather successful at deriving the correct metallicity. As a result, the estimated turn-off ages of these stars yielded by model-fitting are well constrained. Encouraged by this we have fitted these same variable-metallicity models to the deep, optical spectra of the z ≃ 1.5 mJy radio galaxies 53W091 and 53W069 obtained with the Keck telescope. While the age and metallicity are not so easily constrained for these galaxies, we find that even when metallicity is allowed as a free parameter, the best estimates of their ages are still ≥3 Gyr, with ages younger than 2 Gyr now strongly excluded. Furthermore, we find that a search of the entire parameter space of metallicity and star formation history using MOPED leads to the same conclusion. Our results therefore continue to argue strongly against an Einstein–de Sitter universe, and favour a Λ-dominated universe in which star formation in at least these particular elliptical galaxies was completed somewhere in the redshift range z = 3–5 . 相似文献
224.
225.
The IRAS and 2MASS associations for 193 T Tauri stars are identified in this paper. From the color–color diagrams and spectral index, it is found that the IR excesses for most samples are due to thermal emission from the circumstellar material, as suggested previously. It is also found that the IR excesses at IRAS region for few T Tauri stars and the near-IR excesses for some T Tauri stars are likely attributed to free-free emission or free-bound emission from the circumstellar ionized gas. Moreover, It is found in deredened J–H versus H–K color–color diagram that there is a slight separation in different spectral groups. The T Tauri stars locus equation in J–H versus H–K color–color diagram for our sample is also presented. 相似文献
226.
The collisional instability of the drift wave in a multi-component plasma is investigated. It is shown that when the electron and ion density gradients are different, e.g., due to the presence of a static third component or due to neutral drag effects, the drift mode becomes unstable. The instability is caused by the simultaneous action of the electron collisions with all other plasma species and the spatial difference of the density of the plasma components. This instability may be expected as a natural consequence of the stratification of a multi-component plasma placed in an external gravity field where it can operate for any amount of charge on heavy particles. Therefore it could develop in weakly ionized cold interstellar regions for example, when the heavy particles, i.e. charged grains, are a few tens of Å in size, and carry typically ±1,±2 charge. In the solar atmosphere, it may appear in the weakly ionized photospheric layers due to the convective motion of the neutral component. 相似文献
227.
228.
The seasonal variation of the surface temperature is calculated for various idealized paleogeographic conditions with a 1.5-dimensional (1.5-D) coupled climate-sea ice model. The sensitivity of the annual and summer polar temperatures to the meridional oceanic heat transport and to the parameterizations adopted for the snow and sea ice albedos is examined in connection with the location and size of a polar global super-continent. It is shown that the high latitude summer temperatures remain below the freezing point in all numerical simulations with a polar super-continent, thus suggesting the potential role played by a large polar continental mass in the initiation of glaciations. These results are in agreement with a previous 1.5-D energy balance model (EBM) study but in conflict with two-dimensional (2-D) EBMs suggesting above-freezing high latitude summer temperatures in the case of a polar-centered super-continent. It is also found that the amount of seasonality is strongly dependent on the details of the surface albedo feedback parameterizations and could explain the various model diverging results.If a simplified temperature dependence of the silicate weathering rate controlling the long-term carbon cycle is included, the atmospheric CO2 level is significantly increased in the case of a polar-centered continent but summer temperatures still remain below freezing. 相似文献
229.
We study the dynamics of extended shells of relatively low-mass particles around and inside the orbit of two heavy centres of gravity (a binary) by computer simulations. The binary components are surrounded byN = 16 000 small mass particles in uniform random distribution on few spherical envelopes with different radii expanding with respective velocities. Some shells are inside the orbit of binary.We apply this model to binary galaxy systems with baryonic dark matter, e.g., massive black holes. In principle, we can apply this model to different kinds of objects (from binary star systems until superclusters of galaxies).It is shown that the shell expands homologously with a decreasing velocity and then, falls back into the binary system forming zones of compressed matter. At some moment of time there could be a collapse of these particles on to the heavier component of the binary. Further in time, some part of particles which were outside the binary orbit escape from the system. Other particles which were initially inside of the orbit are captured by binary components.We consider a number of different models with different initial parameters. For models with smaller radii of shells, about one-half of the particles escape from systems; whereas for larger values the shell disrupts as a whole. Escaping particles form collimated flows in planes of orbits of binaries. Positions of flows and directions of motion depend on positions of heavier components of binaries at the moment of a closest approach of particles and on ratios of masses of binary components.We show that during evolution of our models different kinds of structures of systems often are very similar to the observed structures of galaxies: spiral and elliptical galaxies, interacting galaxies, different kinds of flows and jets. Totally systems are expanding - after 40 periods of rotation of the binary the system expands by 300 times. 相似文献
230.
The aim of the present paper is to analyze the light variation as well as the period changes of the eclipsing binary RZ Cas. New photometric elements are computed using the frequency-domain method. The possibility of the light-time effect and the apsidal motion is discussed. 相似文献