深圳海岸复杂地形气流与湍流特征的数值模拟     

王卫国  蒋维楣 《气象科学》1997,17(3):274-279

利用三维非静力能量闭合（Ｅ－ε）的边界层模式，以深圳海岸复杂地形进行了实际模拟。结果给出了该地区海陆风情形下气流和湍流孤变化特征。在海风发展盛期，气流方向由大面积的水域和内陆的位置决定，不规则海岸线对局地气流影响不大，夜间陆风时，不规则海岸线对局地气流影响较大，湍流能量高值颁在陆地上空的不稳定层内，水面上湍能很小。模拟结果与实测结果上比较吻合。  相似文献   

论边界层中的大气扩散PDF模式   总被引：3，自引：0，他引：3  

徐大海  朱蓉  李宗恺 《气象学报》1997,55(6):670-680

基于大气扩散Ｋ理论，用作为风速脉动均方差和拉氏时间尺度函数的湍流交换系数，得到了直接利用风速脉动几率密度而不用扩散参数的大气扩散ＰＤＦ模式。分别研究了对流边界层上升气流区与下降区垂直速度的统计特征，求得双正态ＰＤＦ模式。在给定ＣＢＬ自身参数如对流特征速度ｗ＊，顶高ｈｉ和源高度上的平均风速时，该模式计算出的无量纲浓度分布与室内外测试结果一致。  相似文献   

Rapid cooling and exhumation of eclogitic rocks from the Great Caucasus, Russia   总被引：3，自引：0，他引：3  

A. PERCHUK  & P. PHILIPPOT 《Journal of Metamorphic Geology》1997,15(3):299-310

Diffusion modelling of growth-zoned garnet is used in combination with standard geothermometric and geobarometric techniques to estimate cooling and denudation rates from the mafic eclogites of the Red Cliff area, Great Caucasus, Russia. Euhedral garnet porphyroblasts exhibit different degrees of prograde growth zoning depending on the size of the grain (100 μm to several mm in diameter). Zoning patterns are mainly expressed in terms of Fe–Mg exchange, with 100*Mg/(Mg+Fe) increasing from 18–20 to 33–37 from core to rim. Geothermobarometry yields conditions of 680±40 °C and a minimum of 1.6±0.2 GPa and of 660±40 °C and 0.8±0.2 GPa for the high-pressure and retrograde stages of equilibration, respectively. A temperature of 600±40 °C has been recorded for the late-stage metamorphic overprint in the mica schists surrounding the eclogites. Relaxation of garnet zoning profiles was modelled for three different hypothetical P–T –t trajectories, all with an initial temperature of 680 °C and a pressure change of 0.8 GPa. The first two trajectories involve decompression associated with regular cooling down to 660 °C (near isothermal) and 600 °C. The third path is a two-step trajectory comprising near-isobaric cooling down to 600 °C followed by isothermal decompression to 0.8 GPa. These P–T trajectories cover as wide a range of pressure and temperature changes endured by the rocks as possible, thus representing extreme cases for calculating cooling and exhumation rates. Calculations indicate that the zoning pattern of the smallest garnet (i.e. garnet for which the zoning is most easily eliminated during post-growth processes) along the different paths can be preserved for the following average exhumation and cooling rates: path 1, 143 mm a^?1 and 102 °C Ma^?1; path 2, 60 mm a^?1 and 171 °C Ma^?1; path 3, 11–30 mm a^?1 and 200–400 °C Ma^?1. These results are discussed in light of theoretical P–T–t paths extracted from thermal models of regions of thickened crust, and from analogue models of accretionary wedge and continental lithosphere subduction.  相似文献   

Disequilibrium for Ca during growth of pelitic garnet   总被引：14，自引：1，他引：14  

C. B. CHERNOFF  & W. D. CARLSON 《Journal of Metamorphic Geology》1997,15(4):421-438

Compositional zoning in hundreds of almandine-rich garnets in amphibolite by facies micaceous quartzites from the Picuris Range, north-central New Mexico USA, indicates that although Mn, Mg and Fe achieve chemical equilibrium at hand-sample scale during garnet growth, Ca does not. Instead, Ca concentrations at the surface of growing garnets appear to depend strongly on kinetic factors that govern the local chemical environment, yielding disequilibrium for Ca at scales larger than the region immediately surrounding an individual porphyroblast. Detailed zoning profiles were obtained for 371 garnet crystals in a small volume of a single sample of garnetiferous quartzite, and core analyses were made of 97 additional crystals. Each analysis was made on a section that passed precisely through the morphological centre of the crystal, located by means of 3-D imagery from computed X-ray tomography. The data reveal strong correlations between crystal size and concentrations of Mn, Mg and Fe (but not Ca) in garnet cores; a relationship between crystal size and isolation; rigorous cross-correlations among concentrations of Mn, Mg and Fe (but not Ca); and systematic variations in Ca concentrations as a function of crystal size and core composition that are anomalous in comparison to the behaviour of the other divalent cations. We interpret these observations as the result of thermally accelerated diffusion-controlled garnet growth, in circumstances that promoted rapid intergranular diffusion and thus rock-wide equilibration of Mn, Mg and Fe, but that prevented equilibration at similar scale for Ca because of its more sluggish intergranular diffusion. The anomalous behaviour of Ca is made evident in these garnets by the presence of sharp spikes in Ca concentration, which are demonstrably not a consequence of any simultaneous rock-wide event, such as a change in pressure, temperature, or some other intensive parameter. Instead, Ca concentrations probably reflect the local extent of reaction in the immediate vicinity of each porphyroblast. To the degree that such kinetic factors introduce departures from chemical equilibrium for Ca, thermobarometric estimates that involve grossular contents of pelitic garnet will be in error.  相似文献   

A general correspondence principle for time-domain electromagnetic wave and diffusion fields     

Adrianus T. de  Hoop 《Geophysical Journal International》1996,127(3):757-761

A general correspondence principle is presented that relates any time-domain electromagnetic diffusion field to an electromagnetic wavefield in a 'corresponding' configuration. The principle applies to arbitrarily inhomogeneous and anisotropic media and arbitrary transmitters and receivers. For the correspondence between the two types of electromagnetic fields to hold, the electric conductivity in the diffusive case and the permittivity in the wavefield case should have the same spatial variation, while the permeability distributions in space in the two cases are to be identical. Essential steps in the derivation of the correspondence principle are the use of the time Laplace transformation of causal signals, taken at real, positive values of the transform parameter, the Schouten-Van der Pol theorem in the theory of the Laplace transformation, and the reliance upon Lerch's theorem of the uniqueness of the interrelation between causal field quantities and their time-Laplace-transform representations at real, positive values of the transform parameter. Correspondence is then established between the tensorial Green's functions in the two cases, where the Green's functions are the point-receiver responses (either electric or magnetic field) to point-transmitter excitations (either electric- or magnetic-current source).
Through the correspondence principle, all transient electromagnetic wavefields (where losses are neglected) have as a counterpart a transient diffusive electromagnetic field (where the electric displacement current is neglected). The interrelation yields the tool to compare quantitatively the potentialities of the two types of fields in transient electromagnetic geophysical prospecting.
Finally, a general medium-parameter scaling law for time-domain electromagnetic wavefields is presented.  相似文献   

The respiratory environment of the Namib Desert Golden Mole     

Roger S. Seymour  Mary K. Seely 《Journal of Arid Environments》1996,32(4):453-461

We measured the partial pressure of oxygen (PO₂) in the interstitial gas surrounding the sand-swimming Namib moleEremitalpa granti namibensis. At a sand temperature of 26 °C, which produced a nearly maximal rate of oxygen consumption, thePO₂near the noses of the animals averaged only 0·9 kPa (6·7 Torr) below the level in the free atmosphere. High oxygen availability was a result of the notably low metabolic rate in the 20 g mammals and the dry, porous and metabolically inactive nature of dune sand. A mathematical model indicated that normal mammals weighing 200 g or more could comfortably exist completely encased in dune sand. We concluded that the moles' small size and low metabolic rate are not adaptations to hypoxia or hypercapnia underground but are probably related to low food availability and the energetic cost of foraging in their desert environment.  相似文献   

The Influence of Element Diffusion at the Sediment—Water Interface on the Basic Chemical Composition of Overlying Water Mass in Lake Lugu,China     

吴丰昌  万国江等 《中国地球化学学报》1996,15(3):285-288

Little work has been done on the influence of seiments on the basic chemical composition of overlying water mass.This paper deals with the vertical profile of the basic constituents such as Ca^ ,K^ ,Na^ ,and HCO3^-,as well as of pH in the overlying water mass and sediment porewater of Lake Lugu-a semi-closed,deep lake in Yunnan Province.The reand sediment porewater of Lake Lugu- a semi-closed,deep lake in Yunnan Province.The results revealed that those basic constituents may diffuse and transport from bottom sediments to overlying water mass through porewater.In the paper are also quantitatively evaluated the diffusive fluxes and the extent of their influence on overlying water mass,indicating that the lake sediment-water interface diffusion plays an important role in controlling the basic chemical composition of water in the whole lake.  相似文献   

地质速率计—矿物氧扩散的应用     

傅斌  郑永飞 《地球科学进展》1997,12(5):428-433

概述了同位素封闭体系内的矿物氧扩散和同位素交换机制及其在地质速率计上的应用。火成岩从高温冷却或变质岩从高峰主质温度冷却过程中，由于冷却速度不同，扩散作用导致的矿物晶体内部及晶粒间氧同位素再平衡也有所不同。通过实测岩石中各组成矿物氧同位素比值，模式含量和颗粒半径，据矿物氧扩散和同位素交换模型，可以估算出岩石的冷却速率。  相似文献   

Environmental Properties of Minerals and Contaminants Purified by the Mineralogical Method   总被引：2，自引：0，他引：2  

LU Anhuai School of Earth  Space Sciences  Peking University  Beijing 《《地质学报》英文版》2004,78(1):191-202

The investigation of the environmental properties of minerals, i.e., environmental mineralogy, is a branch of science dealing with interactions between natural minerals and spheres of the Earth surface as well as a reflection of global change, prevention of ecological destruction, participation in biomineralogy, and remediation of environmental pollution. Pollutant treatment by natural minerals is based on the natural law and reflects natural self-purification functions in the inorganic world, similar to that of the organic world - a biological treatment. A series of case studies related to natural self-purification, which were mostly completed by our group, are discussed in this paper. In natural cryptomelane there is a larger pseudotetragonal tunnel than that formed by [MnO6] octahedral double chains, with an aperture of 0.462-0.466 nm2, filled with K cations. Cryptomelane might be a real naturally-occurring mineral of the active octahedral molecular sieve (OMS-2). CrⅥ-bearing wastewater can be treate  相似文献   

Global scale annual and semi-annual variations of daytime NmF2 in the high solar activity years     

Tao Yu  Weixing Wan  Libo Liu  Biqiang Zhao 《Journal of Atmospheric and Solar》2004,66(18):1691

The annual and semi-annual variations of the ionosphere are investigated in the present paper by using the daytime F2 layer peak electron concentration (NmF2) observed at a global ionosonde network with 104 stations. The main features are outlined as follows. (1) The annual variations are most pronounced at magnetic latitudes of 40–60° in both hemispheres, and usually manifest as winter anomalies; Below magnetic latitude of 40° as well as in the tropical region they are much weaker and winter anomalies that are not obvious. (2) The semi-annual variations, which are usually peak in March or April in most regions, are generally weak in the near-pole regions and strong in the far-pole regions of both hemispheres. (3) Compared with their annual components, the semi-annual variations in the tropical region are more significant.In order to explain the above results, we particularly analyze the global atomic/molecular ratio of [O/N2] at the F2 layer peak height by the MSIS90 model. The results show that the annual variation of [O/N2] is closely related with that of NmF2 prevailing in mid-latitudes and [O/N2] annual variation usually may lead to the winter anomalies of NmF2 occurring in the near-pole region. Moreover, NmF2 semi-annual variations appearing in the tropical region also have a close relationship with the variation of [O/N2]. On the other hand, the semi-annual variations of NmF2 in the far-pole region cannot be simply explained by that of [O/N2], but the variation of the solar zenith angle may also have a significant contribution.  相似文献