共查询到20条相似文献，搜索用时 46 毫秒
1.
S. N. Grover 《Pure and Applied Geophysics》1976,114(4):521-539
Summary The electrostatic force between a charged conducting sphere and a charged dielectric sphere in a uniform, arbitrarily oriented external electric field is obtained and presented in terms of force coefficients which depend only on the relative geometry of the two spheres and the dielectric constants of the dielectric sphere and the medium. When the dielectric constant of the dielectric sphere is allowed to approach infinity, the resulting computed force agrees with that ofDavis (1964) for two conducting spheres, and when the external field and the charge on the dielectric sphere are set to zero, the resulting force agrees with that ofHall andBeard (1975) for a charged conducting sphere near an uncharged dielectric sphere. 相似文献
2.
Subhash Chandra Ghosh 《Pure and Applied Geophysics》1970,80(1):71-83
Summary The displacement produced in the half-space by uniform impulsive pressure acting over a circular portion of the surface has been obtained in terms of definite integrals. FollowingCagniard andGarvin, the displacement at an interior point on the axis of symmetry has been calculated. The approximate displacement at points far off from the axis of symmetry has been obtained by using saddle point method and Tauberian limit theorem. 相似文献
3.
M. G. S. el Mohandis 《Pure and Applied Geophysics》1969,72(1):155-176
Summary In paper I, (Mohandis [2]2)), the author contributes to the discussion of the origin of the secular variation of the earth's magnetic field. A mathematical solution of magnetohydrodynamic disturbances and fluid motion due to the sudden introduction of an oscillating dipole in the earth's core has been obtained. Only the symmetrical case of the problem, where the axis of the dipole is placed perpendicular to the mantle and parallel to a poloidal field, has been discussed.In this paper, the source of disturbance is still considered to be the oscillating dipole, but the exciting field is taken as a toroidal field always parallel to the mantle. Two unsymmetric different cases of the problem are considered but the disturbed field is sonsidered only in the mantle. It is worth to note here that simpler results can be obtained by applying more conditions than those used in the present work. The new method will be illustrated in a forthcoming paper of this series, Magnetolydrodynamic disturbances in the earth's core, IV where another case of the problem will be discussed. 相似文献
4.
S. G. H. Philander 《地球物理与天体物理流体动力学》2013,107(1):105-123
AbstractThe flow properties of an homogeneous fluid which is bounded by two concentric spheres and two meridional planes which intersect along a diameter of the spheres are investigated. The spheres rotate about this diameter with slightly different angular velocities. As in the axisymmetric case studied by Proudman (1956) and Stewartson (1966) the viscous terms in the equations of motion are important only in boundary layers on the spheres and on the cylinder C which circumscribes the inner sphere and which has generators parallel to the axis of rotation, provided the Ekman number E is small. In the inviscid region the velocities are independent of the coordinate measuring distance along the axis of rotation and are much weaker, by a factor 0(E ½), than the velocities in the Ekman layer on the driving surface (outer sphere). (It is assumed that the reference frame is fixed in the slower rotating inner sphere.) If the separation of the spheres is small compared to their radii then the asymmetric circulation inside C is characterized by an intense jet along the western wall. Loss of fluid from this jet sustains the eastward and northward flow in the inviscid interior where motion is driven by the suction of the Ekman layer on the outer sphere. (Geophysical conventions have been adopted.) Outside C an intense current is present on the eastern, not western, wall while motion in the inviscid region is westward, and away from the axis of rotation. Though there is no transport across C in the inviscid region, the meridional transport of the Ekman layer on the outer sphere is continuous across C and increases, through suction, as the equator is approached until it drains into an eastward flowing equatorial current of width 0(E 1/7). The eastern boundary current outside C and shear layers on C carry this fluid to the intersection of C and the western wall where it feeds the western boundary current inside C.The relation between this study and the experiments of Baker and Robinson (1970) is discussed. 相似文献
5.
2001年3月2日11:00 至11:15 UT 期间,Cluster Ⅱ在南半球极尖区晨侧附近磁鞘内探测到3个通量传输事件（简称FTEs）. 本文利用Cluster Ⅱ星簇4颗卫星观测到的磁场和等离子体资料研究了这些通量传输事件的磁场形态和粒子特征. 并利用它们探测到的空间磁场梯度资料由安培定律直接求出星簇所在区域的电流分布. 结果指出：（1）BY占优势的行星际磁场结构在磁层顶的重联可以在极尖区附近发生;（2）FTEs通量管形成初期内外总压差和磁箍缩应力不一定平衡,达到平衡有一发展过程;（3）FTEs通量管截面在L M平面内的线度约为1.89RE;（4）FTEs通量管中等离子体主要沿轴向场方向流动,整个通量管以慢于背景等离子体的速度沿磁层顶向南向尾运动;（5）FTEs通量管中不仅有轴向电流,也存在环向电流. 轴向电流基本沿轴向磁场方向流动. 轴向和环向电流在管内均呈体分布,因而轴向电流产生的环向磁场接近管心时不断减小到零,而环向电流生成的轴向场则不断增大到极值;（6）在通量管的磁鞘部分观测到磁层能量粒子流量的增强,这表明通量管通过磁层顶将磁鞘和磁层内部连通起来了. 相似文献
6.
B. N. Satpathy 《Pure and Applied Geophysics》1971,90(1):153-162
Summary Expressions are obtained for the currents induced in a conducting sphere placed in an oscillating uniform field. The induced currents are plane circular loops around the axis of symmetry with respect to the external field. Current profiles are presented at three latitudinal planes inside the sphere for three parametric values of
that are of importance in prospecting. Magnetic fields created by these currents loops at a point on the axis of the sphere are calculated. This study reveals some interesting results like the existence of zones contributing positively and negatively to the signal measured outside the sphere and behaviour of these zones with parameter. 相似文献
7.
M. G. S. El Mohandis 《Pure and Applied Geophysics》1969,74(1):45-56
Summary In Paper III (Mohandis [1]2) we considered the sudden introduction of amagnetic dipole in the earth's core to act as a source of disturbance to the exitation field taken as a poloidal one. A symmetrical case was considered where the dipole axis is placed parallel to the original field and perpendicular to the earth's mantle. In the present work, we consider an unsymmetric case where the axis of themagnetic dipole is placed perpendicular to both the mantle and the exitation field which is taken as a toroidal one. A mathematical study is made for the resulting fluid motion in the core as well as for the generated hydromagnetic perturbations in both the mantle and the earth's fluid core. A more powerful method has been adopted than those used in previous cases. 相似文献
8.
Peter Furness 《Geophysical Prospecting》1994,42(5):405-416
The superposition integral expressing the field due to a magnetic source body is relatively simple to evaluate in the case of a homogeneous magnetization. In practice this generally requires that any remnant component is uniform and the susceptibility of the body is sufficiently low to permit the assumption of a uniform induced magnetization. Under these conditions the anomalous magnetic field due to a polyhedral body can be represented in an intuitive and physically appealing manner. It is demonstrated that the components of the magnetic field H can be expressed as a simple combination of the potentials due to two elementary source distributions. These are, firstly, a uniform double layer (normally directed dipole moment density) located on the planar polygonal faces of the body and, secondly, a uniform line source located along its edges. In practice both of these potentials (and thus the required magnetic field components) are easily computed. The technique is applicable to polyhedra with arbitrarily shaped faces and the relevant expressions for the magnetic field components are suitable for numerical evaluation everywhere except along the edges of the body where they display a logarithmic singularity. 相似文献
9.
Takesi Yukutake 《Physics of the Earth and Planetary Interiors》1981,24(4):253-258
An examination of the westward drift of the geomagnetic field indicates that the drift velocity is almost independent of latitude, suggesting a uniform rigid rotation of spherical shape. When the geomagnetic field is separated into standing and drifting components and expressed in a spherical harmonic series, a lack of sectorial terms is noted in the standing field. It is shown that these features are well explained by a stratified core model.The core is supposed to be stratified near the surface where toroidal fluid motions are predominant. In the deeper part, the fluid motion is two-dimensional, forming Taylor columns. A simplified core model is assumed to represent these features, in which the core is divided into two parts, an outer spherical shell that rotates westwards at a uniform rate of 0.3° y?1 and a central sphere in which the two-dimensional columnar motions reside. The toroidal motions in the outer spherical interact with the dipole field to induce the drifting field, whereas the columnar motions generate the standing field through interaction with a toroidal field. It follows that a small velocity as 5 × 10?3 cm s?1 for the stratified motion is sufficient to create the observed drifting field. 相似文献
10.
Ataru Sakuraba 《地球物理与天体物理流体动力学》2013,107(4):291-318
A linear analysis of thermally driven magnetoconvection is carried out with emphasis on its application to convection in the Earth's core. We consider a rotating and self-gravitating fluid sphere (or spherical shell) permeated by a uniform magnetic field parallel to the spin axis. In rapidly rotating cases, we find that five different convective modes appear as the uniform field is increased; namely, geostrophic, polar convective, magneto-geostrophic, fast magnetostrophic and slow magnetostrophic modes. The polar convective (P) and magneto-geostrophic (E) modes seem to be of geophysical interest. The P mode is characterized by such an axisymmetric meridional circulation that the fluid penetrates the equatorial plane, suggesting that generation of quadrapole from dipole fields could be explained by a linear process. The E mode is characterized by a few axially aligned columnar rolls which are almost two-dimensional due to a modified Proudman-Taylor theorem. 相似文献
11.
Summary Expressions are obtained for the currents induced inside a conducting sphere placed in the field of an oscillating magnetic dipole. Interesting conclusions can be drawn from an analysis of the formulas for the current induced due to different orientations of the dipole. 相似文献
12.
A new exact analytical solution of the magnetohydrostatic problem describes the equilibrium of a solitary, dense-cool solar filament maintained against the gravity by magnetic force in hot solar corona at heights up to 20–40 Mm. The filament is assumed to be uniform along the axis (the translation symmetry). The magnetic field of the filament has the helical structure (magnetic flux rope) with a typical strength of a few Gauss in the region of minimal temperature (about 4000 K). The model can be applied to the quiescent prominence of both normal and inverse magnetic polarity.
相似文献13.
P. M. Davis 《Pure and Applied Geophysics》1974,112(5):811-819
Summary A method has been developed to determine the stress distribution and resultant piezomagnetic surface anomaly field due to the load imposed on the earth's crust from filling man-made lakes of variable depths and arbitrary geometries but uniform elastic properties. The dam-magnetic effect observed byDavis andStacey [1] on Talbingo reservoir in the Snowy Mountains of SE Australia is adequately explained in terms of the piezomagnetic effect if more highly magnetic rock than that measured on the surface is present at depth. 相似文献
14.
15.
A. Tilgner 《地球物理与天体物理流体动力学》2013,107(3):225-234
In geodynamo simulations which simulate the generation of an axial dipolar magnetic field, the generation mechanism appears to be adequately described as an α2-dynamo with an anisotropic α-effect. The anisotropy in the α-effect favors an equatorial dipole field, however, which calls into question the interpretation in terms of an α2-dynamo. It is shown in this article with kinematic dynamo calculations and exemplary velocity fields with an anisotropic α-effect that both types of dipolar magnetic field can be generated. Two examples of working dynamos in a sphere with flows with zero α-effect are also provided. 相似文献
16.
In applied studies on electromagnetic well-logging and electric prospecting, a medium is supposed to be either isotropic or
with conventional anisotropy of conductivity. However, in the meantime, there is a clear hint that a medium may exhibit even
biaxial anisotropy; i.e., the resistances along all three directions X, and Y, Z are different. Based on the analytical solution by the method of separation of variables, the paper considers an algorithm
for the calculation of the electromagnetic field in a layered medium with biaxial conductivity anisotropy involving an arbitrary
direction of horizontal conductivities in each layer. In this case, the theoretical solution and the algorithm display substantial
peculiarities, and the numerical implementation involves many complexities. These problems were examined and solved mainly
due to the constant comparison with the calculations carried by the finite element method and their analysis. Programs for
the calculation of electromagnetic fields in the frequency and time domains were developed, and results of geoelectric interest
were obtained. For example, the excitement of a horizontally-layered section by a magnetic dipole produces a vertical electric
component of the field. 相似文献
17.
The steady velocity, perturbation pressure and perturbation magnetic field, driven by an isolated buoyant parcel of Gaussian shape in a rapidly rotating, unconfined, incompressible electrically conducting fluid in the presence of an imposed uniform magnetic field, are obtained by means of the Fourier transform in the limit of small Ekman number. Lorentz and inertial forces are neglected. The solution requires at most evaluation of a single integral and is found in closed form in some spatial regions. The solution has structure on two disparate scales: on the scale of the buoyant parcel and on the scale of the Taylor column, which is elongated in the direction of the rotation axis. The detailed structures of the flow and pressure depend linearly on the relative orientation of gravity and rotation, with the solution for arbitrary orientation being a linear combination of two limiting cases in which these vectors are colinear (polar case) and perpendicular (equatorial case). The perturbation magnetic field depends additionally on the relative orientation of the imposed magnetic field, and three limiting cases of interest are presented in which gravity and rotation are colinear (polar–toroidal case), gravity and imposed field are colinear (equatorial–radial case) and all three are mutually perpendicular (equatorial–toroidal case). Visualization and analysis of the velocity and perturbation magnetic field vectors are facilitated by dividing these vector fields into geostrophic and ageostrophic protions. In all cases, the geostrophic and ageostrophic portions have different structure on the Taylor-column scale. The buoyancy force is balanced by a pressure force in the polar case and by a flux of momentum in the equatorial case. The pressure force and momentum flux do not decay in strength with increasing axial distance. Far from the parcel, the axial mass flux varies as the inverse one-third power of distance from the parcel. The velocity has a single geostrophic vortex in the polar case and two vortices in the equatorial case. The perturbation magnetic field has two, four and one geostrophic vortices in the polar–toroidal, equatorial–radial and equatorial–toroidal cases, respectively. To facilitate comparison of the present results with numerical simulations carried out in a finite domain, a set of boundary conditions are developed, with may be applied at a finite distance from the parcel. 相似文献
18.
The electric field generation at the front of the current pulse, which originates in a coronal magnetic loop owing to the development of the Rayleigh–Taylor magnetic instability at loop footpoints, has been considered. During the τA ≈ l/V A ≈ 5?25 s time (where l is the plasma plume height entering a magnetic loop as a result of the Rayleigh–Taylor instability), a disturbance related to the magnetic field tension B ?(r,t), “escapes” the instability region with the Alfvén velocity in this case. As a result, an electric current pulse Iz(z ? V A t), at the front of which an induction magnetic field E z, which is directed along the magnetic tube axis and can therefore accelerate particles, starts propagating along a magnetic loop with a characteristic scale of Δξ ≈ l. In the case of sufficiently large currents, when B ? 2/8π > p, an electric current pulse propagates nonlinearly, and a relatively large longitudinal electric field originates E z ≈ 2I z 3 V A/c 4a2Bz 2l, which can be larger than the Dreicer field, depending on the electric current value. 相似文献
19.
Willis L. Webb 《Pure and Applied Geophysics》1971,84(1):89-108
Summary The atmospheric electrical structure of the earth is postulated to be controlled by a motivating force in the lower ionosphere which is produced by interaction between neutral atmosphere tidal circulations and the ionospheric plasma in the presence of the earth's magnetic field. Associated electric fields power the dynamo currents through the Hall effect with a resulting development of a gross electric potential distribution in the lower ionosphere. Asymmetries in these hemispheric potential distributions result in exospheric current flows in lowL-shells and larger differences in potential produced by dynamo return current flows in high magnetic latitudes result in strong currents through highL-shells between auroral zones. Vertical thunderstorm currents with their associated lightning discharges effectively connect the earth to a low potential region of the dynamo circuit and thus supply the earth with an average negative charge which motivates a leakage tropospheric electrical circuit. In addition, the dynamo currents maintain the magnetic polar regions at different potentials with a resulting electrical exchange with the solar wind through the earth's near space. These considerations indicate that observed electrical and variable magnetic phenomena near the earth are all part of a single comprehensive electrical current system.This paper was read byH. Dolezalek in an abbreviated form supplied by the author. 相似文献
20.
Summary Using the results of spherical harmonic analyses of the geomagnetic field for some fourteen different epochs, includingGauss' first analysis for epoch 1835, and theErman-Petersen analysis for epoch 1829, the strength and axes of geomagnetic multipoles have been computed. In particular, a dipole from the three first order spherical harmonic coefficients, a quadrupole from five second order coefficients, and an octupole from seven third order coefficients. The axes of the quadrupole and octupole have moved quite rapidly when compared with movements of the dipole axis, and show a general movement westwards. Although the strength of the dipole has generally diminished, the strengths of the quadrupole and octupole have generally increased.On leave National University of La Plata, Argentina 相似文献