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1.
在磁化磁场为恒定磁场（无定向磁力仪─-Ａ）与１０ｋＨｚ交变磁场（ＭｉｎｉｓｅＰ旋转磁力仪─-Ｍ）的两种情况下，作岩样比测时发现，后者测得的主磁化率值кＭ较小，而且沿磁性叶理面方向ｆ的主磁化率值кｍａｘ与кｉｎｔ比沿其法线方向ｎ上的кｉｎｔ减少得更多．作者以涡流磁滞机构对磁性载体材料的“磁屏蔽”作用发生了各向异性的影响来解释此现象；并推测磁化率各向异性存在频散现象． 相似文献
2.
F. Hrouda 《Studia Geophysica et Geodaetica》2007,51(3):423-438
The anisotropy of magnetic susceptibility (AMS) within the Rayleigh Law range was investigated theoretically, using mathematical
modelling. It was revealed that the orientations of the principal susceptibilities and the shape parameter vary with field
so weakly that these variations can be regarded as negligible from the practical point of view. The degree of AMS increases
with field according to the degree of anisotropy of the initial susceptibility used and according to the intensity of susceptibility
change with field of the mineral considered. The degree of AMS calculated using linear theory is very near to the degree of
AMS following from the analysis of AMS within the Rayleigh Law range. If it is desirable to correct the field-dependent degree
of AMS, a simple technique is suggested based on measurement of the AMS in two fields.
fhrouda@agico.cz 相似文献
3.
猴石顶太古界重褶皱位于阜平太古宙穹状复合褶皱群中一个钩状褶皱的“钩子”部位。其中一层斜长角闪岩标志层的岩石磁性组构的分布情况为:1.在翼部的磁化率量值椭球是压扁形的,磁性叶理面的方向与变质层面及片麻理的方向基本一致,表现为向北西倾斜的倒转褶皱;2.在太古宙再次变形阶段所形成的转折端部位,磁性叶理面的走向变化较大,并出现拉长形的磁化率量值椭球,反映了经受过拉张作用的变形和多于一次的不同方向应力的作用;3.西翼的磁性线理值与磁性叶理值以及磁化率各向异性度都大,反映它经受过较强的剪切应力与压应力的作用;4.磁性线理主要倾向北半球,而且部分磁性线理近南北方向分布。 推测猴石顶重褶皱可能处于向北倾伏的主体构造的东侧。 上述岩石磁性是由自行设计的静态测量方法,用国产的数字式无定向磁力仪测定的。 相似文献
4.
《Physics of the Earth and Planetary Interiors》2003,135(2-3):137-159
We experimentally characterize magnetic field fluctuations in a strongly turbulent flow of liquid sodium in the presence of a large externally applied field. We reach high interaction parameter (up to N=17) for moderate magnetic Reynolds number (up to Rem=18), a previously unexplored parameter range for liquid metal flows. As the interaction parameter (i.e. the ratio of Lorentz to inertial forces) is increased, the system passes through distinct regimes, which we classify. We find that for certain ranges of the applied magnetic field, particularly at high values, the induced magnetic field exhibits large, coherent oscillations. Spatial structure in these induced field oscillations suggests the formation of non-axisymmetric vortices that precess at a fraction of the impeller rotation rate. We also investigate the effect of rough versus smooth boundaries and relate these results to topographic core–mantle coupling in the Earth. 相似文献
5.
V.A. Osherovich J. Fainberg R.F. Benson R.G. Stone 《Journal of Atmospheric and Solar》1997,59(18):2361-2366
We study cylindrical oscillations of electrons in a plasma where the background magnetic field is parallel to the axis of a cylinder and the ion background is taken to have a constant positive density. Assuming self-similarity, we reduce the problem to two second order nonlinear differential equations, relating fluctuations of electron density and fluctuations of magnetic field. The system studied is shown to have two fundamental frequencies. In the linear domain, these frequencies correspond to the Z and X cold plasma wave cutoff frequencies (R = 0 and L = 0 conditions in the notation of Stix (1992), respectively). Thus they differ by the gyrofrequency. In the nonlinear domain, these frequencies change and resonances at harmonics and at the sum and difference frequencies appear. When the plasma/gyro frequency ratio is close to an integer, our results indicate special resonance conditions which are characterized by an increase of the amplitude and a narrowing of the fundamental resonances. 相似文献
6.
Summary A magnetic study of metabasic dykes of pre-Cambrian age in Gomoh has been done. 9 magnetic profiles have been taken with Schmidt vertical force variometer. Direction and intensity of NRM have been determined for 25 oriented samples with an astatic magnetometer. Magnetic susceptibility of the samples has been determined. The magnetic profiles have been interpreted by considering both natural remanence and susceptibility of the rock samples. The remanent magnetic directions have two groups, one corresponding to the northern hemisphere and the other to the southern hemisphere. The corresponding latitudes of the place would then be 34°N and 42°S. It is suggested here that metamorphism of the basic rocks of this area took place during two distinct geologic epochs, one when India was in northern hemisphere and the other when in southern hemisphere, presuming that continental drift has taken place. 相似文献
7.
John V. Shebalin 《地球物理与天体物理流体动力学》2013,107(3):353-375
We consider an unforced, incompressible, turbulent magnetofluid constrained by concentric inner and outer spherical surfaces. We define a model system in which normal components of the velocity, magnetic field, vorticity, and electric current are zero on the boundaries. This choice allows us to find a set of Galerkin expansion functions that are common to both velocity and magnetic field, as well as vorticity and current. The model dynamical system represents magnetohydrodynamic (MHD) turbulence in a spherical domain and is analyzed by the methods similar to those applied to homogeneous MHD turbulence. We find a statistical theory of ideal (i.e. no dissipation) MHD turbulence analogous to that found in the homogeneous case, including the prediction of coherent structure in the form of a large-scale quasistationary magnetic field. This MHD dynamo depends on broken ergodicity, an effect that is enhanced when total magnetic helicity is increased relative to total energy. When dissipation is added and large scales are only weakly damped, quasiequilibrium may occur for long periods of time, so that the ideal theory is still pertinent on a global scale. Over longer periods of time, the selective decay of energy over magnetic helicity further enhances the effects of broken ergodicity. Thus, broken ergodicity is an essential mechanism and relative magnetic helicity is a critical parameter in this model MHD dynamo theory. 相似文献
8.
Alexander K. H. Pazur 《地球物理与天体物理流体动力学》2014,108(5):536-552
Seawater is the major heat transporter in our global environment, covering more than two-thirds of the surface of the earth. With an average salinity of ～3.5%, it is a moderate electric conductor, which is permanently in motion by thermal and hydrodynamic forces. A magnetic field exerts a Lorentz force on seawater that principally influences both the dissipation of turbulence and the flow properties by magnetic friction. Here we show by experiments on laboratory scale that convection in seawater is slowed down by an external static magnetic field and leads to a reduced heat flux resulting in an increased or decreased heat content in the volume in response to influx or drain of heat, respectively. Experimentally, the application of a vertical magnetic field of 60 mT reduces the convective heat transport on the liquid-air surface within in 5 min by about 8% perpendicular to the field and up to 14% parallel to it. The effect is strongly correlated with the magnetic interaction parameter of the system, which relates the magnetic to the viscous volume force. In the natural environment, the geomagnetic field is omnipresent. It is weaker by about three orders of magnitude compared with the magnetic field applied in the experiments. It has, however, an undisturbed and long-lasting impact on the convection, at low Reynolds numbers, in the large body of water in the deeper ocean below the mixed layer. There are no investigations regarding a possible contribution of this effect to natural saltwater flows, neither by proxy experiments nor by model calculations. The data presented raise the possibility that convective heat transport in the sea could be always slowed down by the geomagnetic field to a certain extent, besides it could be modulated by the geomagnetic secular variation on relatively short timescales like decades. 相似文献
9.
The parameter of cosmic ray fluctuations, which indicates the degree of IMF inhomogeneity, was introduced in order to quantitatively
describe the dynamics of the galactic cosmic ray (GCR) intensity fluctuations during the geoeffective phases of the 11-year
cycle. The 5-min data of the high-latitude neutron monitor at Oulu station (Finland) during cycles 20–23 was used in the calculations.
The nonrandom non-Gaussian character of the GCR fluctuation parameter is caused by the nonstationary semiannual variation
reflecting the transient nonstationary oscillatory process of sign reversal of the general solar magnetic field. This transient
oscillatory process is responsible for the maximal geoeffectiveness and duration of the phase of polarity reversal, which
manifests itself in a sharp and deep GCR intensity minimum during the final stage of the field sign reversal. The invariant
of the 11-year “amplitude-duration” cycle was confirmed on a new basis: the LF drift of the “low” cycle period was detected,
which was observed in an increase in the duration of cycle 23 we anticipated. 相似文献
10.
航空电磁法的探测能力受飞行高度、发射波形、发射磁矩和发射基频等因素的影响,致使不同分量间的勘探能力存在差异.航空电磁如对所有磁场和磁感应分量、on-和off-time数据进行观测和解释,不仅数据量大、耗时长,而且出现大量冗余数据.目前国内针对此问题尚无系统解决方法.本文针对吊舱式直升机航空电磁系统,采用积分方程法求解频率域响应,经汉克尔变换转换到时间域,计算了地下三维目标体的B和dB/dt时间域响应.利用异常体响应与背景场响应作比值,并通过设定响应阀值定义最大勘探深度,进而分析不同发射波形、不同分量以及on-和off-time期间的航空电磁系统的探测能力.基于本文分析手段,可根据实际勘探目标,确定一套探测能力较强的航空电磁最佳参数组合,为野外测量和数据处理提供技术指导,高效完成勘探任务. 相似文献
11.
12.
M. Yu. Reshetnyak 《Izvestiya Physics of the Solid Earth》2017,53(4):581-587
Parker’s two-dimensional (2D) dynamo model with an algebraic form of nonlinearity for the α-effect is considered. The model uses geostrophic distributions for the α-effect and differential rotation, which are derived from the three-dimensional (3D) convection models. The resulting configurations of the magnetic field in the liquid core are close to the solutions in Braginsky’s Z-model. The implications of the degree of geostrophy observed in the 3D dynamo models for the behavior of the mean magnetic field are explored. It is shown that the reduction in geostrophy leads to magnetic field reversals accompanied by the relative growth of the nondipole component of the field on the surface of the liquid core. The simulations with a random α-effect which causes turbulent pulsations are carried out. The approach is capable of producing realistic sequences of magnetic reversals. 相似文献
13.
Summary The effect of an additional homogeneous magnetic field with an intensity of 0–4.5 Oe on the Worden quartz gravity meter No. 961 and on Sharpe quartz gravity meters Nos 173 and 174 was tested. Whereas no effect was observed with the Worden gravity meter, the magnetic field had a measurable effect on both the Sharpe gravity meters. The largest deviation of the reading beam is caused by the horizontal component of the magnetic field which acts in the plane of oscillation of the gravity-meter arm. The Sharpe gravity meter No. 173 is considerably sensitive; a field of 0.2 Oe intensity, corresponding to the magnitude of the horizontal component of the geomagnetic field in mid-latitudes, causes an error in the measurement of gravity of as much as 0.08 mGal. With a view to the different behaviours of the individual quartz gravity meters of the same type in a magnetic field, it should prove expedient to carry out check measurements with all gravity meters and, with regard to the sensitivity of the gravity meter to the magnetic field and the required accuracy of the gravity determination, take into account this perturbing factor in field measurements, as well as laboratory tests of gravity meters. 相似文献
14.
S. O. Feofilaktov S. N. Rychagov Yu. Yu. Bukatov I. A. Nuzhdaev A. A. Nuzhdaev 《Journal of Volcanology and Seismology》2017,11(5):353-366
This paper is concerned with a discussion of a fundamental problem in geothermal research, that of reaching an understanding of the structure and physical nature of zones of thermal discharges, taking the Pauzhetka hydrothermal system as an example along with the eponymous geothermal field situated at the southern tip of Kamchatka. We combined geological and geophysical results from magnetic surveying, electrical surveying, gravity surveying, soil thermometry, pitting and well drilling in hydrothermal clay, to carry out a detailed study of a large zone of hydrothermal discharges in the structure of this hydrothermal system, that is, the East Pauzhetka thermal field. We identified a system of blocks that control aquifers, mineralization zones at the base of the sequence of hydrothermal clay, steam-charged and water-saturated volumes, and volumes where ascending hydrothermal brines circulate via fissures and pores. We hypothesize the existence of a shallow (a few tens of meters) top of a subintrusive body of an intermediate or basic composition. The intrusion of that body may have given rise to the formation of a tectono-magmatic uplift in the East Pauzhetka thermal field. The resulting geological and geophysical data stimulate multidisciplinary surveys of other areas in the Pauzhetka geothermal field and make their contribution to the solution of a major scientific and applied problem, which is to determine the source of heat for the field. 相似文献
15.
S. D. London 《地球物理与天体物理流体动力学》2013,107(3-4):251-268
Abstract Numerical work indicates that resistive instability may be the dominant mode of instability in the Earth's outer core for realistic core parameter regimes. In this paper, we assume that the Elsasser number is large in order to obtain an asymptotic analysis of resistive instability in an electrically conducting fluid confined to a rotating cylindrical shell of infinite extent in the axial direction. The dimensionless equations of motion are linearized about an ambient magnetic field which is purely azimuthal and depends only on the cylindrical radial variable. Applying the theory of ordinary differential equations with a large parameter, we obtain an asymptotic approximation to the solution. Relatively simple analytic expressions for the complex frequencies are obtained by applying the boundary conditions for insulating boundaries at the cylindrical sidewalls and then assuming that the ambient magnetic field vanishes at one or both of those sidewalls. The results appear to be consistent with previous numerical work. 相似文献
16.
The nonlinear perturbation of a dipole field by a system of transverse currents, which arises due to the radial pressure distribution when the pressure is almost independent of the radial distance, is analyzed. This distribution of pressure was observed in the experiment. The radial dependences of the magnetic field depression, transverse current density, and volumes of magnetic flux tubes have been obtained at different values of the plasma parameter via nonlinear simulation. It is shown that a dependence of the volume of magnetic flux tube on the radial distance can change and a region of the negative gradient of volume can appear at some plasma-parameter values. 相似文献
17.
The characteristics of substorm-associated Pi2 pulsations observed by the SABRE coherent radar system during three separate case studies are presented. The SABRE field of view is well positioned to observe the differences between the auroral zone pulsation signature and that observed at mid-latitudes. During the first case study the SABRE field of view is initially in the eastward electrojet, equatorward and to the west of the substorm-enhanced electrojet current. As the interval progresses, the western, upward field-aligned current of the substorm current wedge moves westward across the longitudes of the radar field of view. The westward motion of the wedge is apparent in the spatial and temporal signatures of the associated Pi2 pulsation spectra and polarisation sense. During the second case study, the complex field-aligned and ionospheric currents associated with the pulsation generation region move equatorward into the SABRE field of view and then poleward out of it again after the third pulsation in the series. The spectral content of the four pulsations during the interval indicate different auroral zone and mid-latitude signatures. The final case study is from a period of low magnetic activity when SABRE observes a Pi2 pulsation signature from regions equatorward of the enhanced substorm currents. There is an apparent mode change between the signature observed by SABRE in the ionosphere and that on the ground by magnetometers at latitudes slightly equatorward of the radar field of view. The observations are discussed in terms of published theories of the generation mechanisms for this type of pulsation. Different signatures are observed by SABRE depending on the level of magnetic activity and the position of the SABRE field of view relative to the pulsation generation region. A twin source model for Pi2 pulsation generation provides the clearest explanation of the signatures observed. 相似文献
18.
O. V. Mingalev I. V. Mingalev V. S. Mingalev M. L. Khodachenko 《Geomagnetism and Aeronomy》2009,49(5):574-581
The problem of a smooth field configuration, which should be an initial configuration in modeling (using the method of coarse particles) the problem of a stationary solar wind flow around a magnetic cloud in the case of a spatially two-dimensional statement (when a magnetic cloud is considered as a force-free magnetic cylinder with a finite radius) is considered. It has been indicated that such a statement is possible only when the magnetic field in the solar wind is parallel to the cylinder axis. The method for finding the magnetic field of a force-free cylinder with a finite radius, when some field component is specified and another component is determined based on this one (which makes it possible to construct fields with preassigned properties), has been proposed. The variant for constructing the initial field configuration in the transition region around a cylinder has been proposed. This variant makes it possible to gradually pass from homogeneous crossed fields in the solar wind to a force-free magnetic and zero electric fields within a cylinder, an electric field being potential and orthogonal to a magnetic field (in the reference system related to a magnetic cloud). 相似文献
19.
In the current state of geomagnetic instrument testing, some aspects of geomagnetic instrument performance are difficult to test in the laboratory. If laboratory test results are inadequate, the instrument will have multiple problems while operating in the field, where a geomagnetic instrumentation test platform with a stable natural magnetic field is critical. Here, the magnetic field feedback circuit for geomagnetic field compensation control is studied in detail. That is, the magnetic field measured by the feedback magnetic sensor and the required working magnetic field are compared as input to the system, and the electric signal is transmitted to the feedback coil through an analog circuit to form a closed loop control, which provides compensation to control the magnetic field. Compared with the existing magnetic shielding method, the analog control circuit can achieve the realization of any working magnetic field, and it is not limited to a null magnetic field. The experimental result shows that the system compensates the earth''s magnetic field of 10,000nT with an average error of 10.6nT and average compensation error of 0.106%, providing a high compensation accuracy. The system also shows high sensitivity and excellent stability. The feedback circuit has achieved effective compensation control for the earth''s magnetic field. 相似文献
20.
Masaki Matsushima 《地球物理与天体物理流体动力学》2013,107(6):630-642
A thermal diffusive process in the Earth's core is principally enhanced by small-scale flows that are highly anisotropic because of the Earth's rapid rotation and a strong magnetic field. This means that a thermal eddy diffusivity should not be a scalar but a tensor. The effect of such anisotropic tensor diffusivity, which is to be prescribed, on dynamics in the Earth's core is investigated through numerical simulations of magnetoconvection in a rapidly rotating system. A certain degree of anisotropy has an insignificant effect on the character, like kinetic and magnetic energies, of magnetoconvection in a small region with periodic boundaries in the three directions. However, in a region with top and bottom rigid boundary surfaces, kinetic and magnetic energies of magnetoconvection can be altered by the same degree of anisotropy. This implies that anisotropic tensor diffusivity affects on dynamics in the core, in particular near the boundary surfaces. 相似文献