Infrasonic wave magnetic field in the oceanic waveguide

The magnetic field generated by an acoustic wave, propagating in the oceanic wave guide, has been considered. It has been indicated that the induced field is most substantial at frequencies when only the first normal mode exists. The dependences of the induced field component on the depth, frequency, and direction of the geomagnetic field have been obtained in this frequency band. The possibility of determining coordinates of a strong underwater earthquake using the acoustic field magnetic field has been considered.     

Magnetic field of a nonstationary point acoustic source in a deep sea

The magnetic field generated by an acoustic wave from a nonstationary point source in an infinite marine medium has been considered. The spatial-temporal structure of the induced field has been studied in a quasistatic approximation and taking into account self-induction. The magnetic field in the transient and stationary regimes has been considered.     

Special points in 11-year variations in the latitudinal characteristics of sunspot activity

It has been indicated that special moments (turning points), when certain characteristics of the latitudinal (equatorward) drift of the sunspot drift zone suddenly change, exist in each 11-year solar cycle. The moment when a sunspot formation low-latitude boundary minimum (T2), coordinated in time with the end of a polar magnetic field polarity reversal, exists has a special place among these points. A conclusion has been drawn that it is impossible to reconstruct polarity reversal moments in the past based on information about turning points T2. The average velocities of the latitudinal drift of the minimal, average, and maximal sunspot group latitudes have been calculated. It has been indicated that the closeness of the relationship between the first two velocities and the maximal activity amplitudes in the cycles differ substantially for the first (before point T2) and second (after point T2) cycle parts. The corresponding values of the correlation coefficients increase substantially in the second cycle (after point T2). It has been established that a relationship exists between some velocities calculated in these cycles and the activity amplitudes at maximums of the next cycles. A model for predicting future cycle maximums has been constructed based on this conclusion. The probable average annual Wolf number at a maximum of cycle 24 has been determined (W(24) = 93).     

Numerical thin-sheet modelling of the telluric field distortions by the hybrid technique. I. Theory and an example for the Baltic Shield

The distortions of the electromagnetic-plane wave field, due to near-surface conductivity inhomogeneities, are considered. The real three-dimensional distribution of the shallow conductivity is approximated by Price's thin-sheet model. As low-frequency magnetotelluric variations are considered it is possible to neglect the self-induction in the thin sheet.The calculation of the current function has been carried out by the alternative Schwarz method. The method combines, in the iterative sense, the finite element solution in the inhomogeneous region and the analytical solution outside of it. The primary electric field is assumed to be circularly polarized. An example for the Baltic Shield shows that the telluric field is mostly very distorted.     

Usage of the near-Earth electric field for detecting underground inhomogeneities

It has been indicated that the electric field that exists above the Earth’s surface contains information about the structure of underground inhomogeneities. Equations have been obtained and are used to illustrate the numerical calculations of the electric field strength along the Earth’s surface and some types of underground objects.     

Electron acceleration in the magnetosphere by whistler-mode waves of varying frequency

Acceleration of relativistic electrons in an inhomogeneous geomagnetic field during their resonant interaction with longitudinally propagating whistler-mode waves of varying frequency has been considered. Specific features of acceleration of electrons trapped by the wave field have been studied. Previous estimates of the efficiency of such acceleration have been generalized with regard to relativistic effects, and the simple formula for energy gain in a wide range of initial energies has been obtained. It has been indicated that the energy gain during a single interaction between electron and a whistler-mode wave packet, with typical parameters of an element of chorus emissions in the Earth’s magnetosphere, can reach several keV. The conditions of this acceleration mechanism realization are discussed. Specifically, it has been found that, in the case of chorus emissions in the Earth’s magnetosphere, this mechanism can be effective for electrons with perpendicular energies several times as high as such an energy of electrons generating chorus.     

Conditions for MAC-wave stability in the Earth’s core

The condition of stability for the model of MAC-wave propagation in the toroidal region with an infinite radius and the numerical results in the toroidal region with a finite radius have been obtained analytically, taking into account a nonuniform distribution of the magnetic field and compressibility. It has been indicated that the frequency of unstable MAC-waves depends on the azimuthal velocity. Instability mostly develops in the Earth’s outer core with a decreased value of the azimuthal magnetic field. It has been qualitatively indicated that close drift velocities are typical of multiple-frequency variations. The MAC-wave frequencies for instabilities that develop near the outer boundary decrease if compressibility of a substance in the Earth’s outer core is taken into account.     

VERTICAL FREQUENCY EFFECT SOUNDING IN INDUCED POLARIZATION AND GALVANIC RESISTIVITY METHODS *

It has been shown that for a polarizable layer as a transmission medium there is an indirect proportionality between the frequency effect (fe) in induced polarization (IP) and the wave number of the electrical induced field. Making use of this relationship for a two layered earth a polarization transform function has been obtained. Since the mathematical expression for the polarization transform function is the same as that of the resistivity transform function, it is possible to make direct interpretation for IP frequency effect field curves. Thus, AA or QQ type resistivity sequences can be interpreted from induced polarization response of a horizontally stratified earth without resistivity extrema. A depth factor has been defined in order to obtain the true depth using the apparent depth. In this way, some electromagnetic effects between horizontal layers with different polarizabilities can partly be eliminated.     

Plumes of the plasmasphere and variations in the geomagnetic field horizontal component

The effects of the dayside and dusk plumes of the plasmasphere during the ring current recovery phase on the disturbance level of the ground geomagnetic field horizontal component have been considered. It has been indicated that the geomagnetic field horizontal component changes specifically and synchronously in the region corresponding to the plasmaspheric dayside plume. Outside the plume the time variations in the geomagnetic field horizontal component pronouncedly differs. A spectral analysis of disturbances in the geomagnetic field horizontal components in the range of geomagnetic pulsations indicated that the intensity in the range of Pc4 pulsations increases at magnetic stations located on field lines corresponding to the dayside and dusk plumes of the plasmasphere. These pulsations detected in the dynamic spectrum of the geomagnetic field horizontal components in the dayside plume region of the plasmasphere, probably reflect the resonance oscillations of magnetic field lines in the region of field-aligned currents at comparatively low altitudes. We assume that this is caused by the instability of field-aligned currents originating as a result of the interaction between the ring current energetic ions and electromagnetic waves in the region with a relatively dense background plasma of the dayside plume.     

Nonlinear modification of magnetospheric plasma under the action of the ULF-wave ponderomotive force on the dayside

Nonlinear modification of the plasma magnetospheric density near the dayside magnetospheric boundary, caused by the ponderomotive force induced by ULF geomagnetic pulsations, has been studied analytically and numerically. An expression for the ponderomotive force, which differs from the previous similar results, has been obtained. It has been indicated that the well-known Pitaevskii formula for magnetic moment is incomplete. The action of the ponderomotive, gravitational, and centrifugal forces on magnetospheric plasma modification in a two-dipole geomagnetic field according to the (Antonova and Shabanskii, 1968) model has been considered.     

川滇强震前地下流体短临前兆综合信息特征

本文选取川滇相对均匀分布的地下流体观测台点的资料,提取其中的中高频信息,然后采用幂函数衰减的方式进行中高频信息场的空间曲面拟合,研究相同物理量的多测点的短临综合信息场.川滇地下流体短临综合信息空间扫描结果表明:在川滇强震发生前短期内孕震邻近区域的短临综合信息明显出现,且大幅度起伏变化;川滇地下流体短临综合信息时间扫描结果表明:川滇强震发生前3个月内中高频信息均表现出较大幅度的增强波动变化,从而突出了震前的多台异常综合信息.     

随钻声波测井FDTD模拟及钻铤波传播特性研究

幅度大的钻铤波掩盖地层信号是困扰随钻声波测井技术的难题,认识钻铤波特性对于消除或有效降低钻铤波至关重要.记录岩石动电效应引起电磁场的随钻动电测井,被认为有望彻底解决钻铤波干扰问题.本文采用有限差分法,模拟不同钻铤、不同井孔结构的随钻声场,对比分析了单极源钻铤波的传播特性,阐明存在伴随钻铤波动电信号的原因.结果表明:钻铤声波在沿钻铤传播时向外部介质辐射能量,透过井壁进入地层的具有视钻铤波速度的声波,与地层纵横波一样可发生动电转化,因而可导致随钻动电测井时产生钻铤波速度的电磁信号.计算还表明,高频情况下,随钻声波测井钻铤波呈现两阶模式:具有低频截止频率的高阶钻铤波幅度较小,其速度略低于钻铤纵波速度;无截止频率的低阶钻铤波幅度较大,其波速在高频时甚至低于钻铤横波速度.这种频散特性和多阶模式特性,是径向多分层开波导结构的导波属性.     

Magnetic cloud in the solar wind: A comparison with the classical model

The solar wind magnetic field distribution near the Earth has been studied and compared with the distribution anticipated according to the classical model. It has been indicated that a two-hump distribution of the IMF values discovered previously is not an artifact of averaging but reflects the actual structure of the magnetic field within the sector. In this case the magnetic field of polarity corresponding to the leading spot in the Northern Hemisphere is encountered more frequently. Not only the magnetic field magnitude but also the fields of either polarity increase with increasing activity. The distance between the peaks on the histogram of the magnetic field near the Earth increases from 6 to 10 nT. The quasi-22-year, 11-year, and quasibiennial (2.6 ± 0.3 years) cycles are observed in an alternate increase in the peaks, in the strength of the fields of either polarity, and in the ratio of the peaks to the occurrence frequency of zero values, respectively. The classical model is violated in approximately 25% of cases.     

Effect of a self-induced electric field on the electron beam kinetics and resulting hard X-ray and microwave emissions in flares

The kinetics of beam electron precipitation from the top of a loop into the solar atmosphere with density gradients and an increasing magnetic field have been generally described. The Fokker-Planck equations are solved with regard to Coulomb collisions and the effect of the electric field induced by this beam. The photon spectra and polarization degree in hard X-ray (10–300 keV) and microwave (1–80 GHz) emissions are simulated under different assumptions regarding the beam electron distribution function. The simulation results are compared with the flare observations on March 10, 2001, and July 23, 2002, visible at different position angles. It has been indicated that the coincidence of the theoretical photon spectra with simultaneous observations of the hard X-ray and microwave emissions of these flares is the best for models that not only take into account collisions, but also the electric field induced by electron fluxes propagating in flare loops with very weakly or moderately converging magnetic fields.     

Wave emission during a plasma density jump in the auroral zone of the topside ionosphere according to the APEX satellite data

The intensity of the wave emission in the 0.1–10 MHz band measured in the ionosphere (the APEX satellite experiment) has been presented. A jump of the plasma density and an increase in the emission intensity at a plasma frequency have been registered at altitudes of ～1300 km in the topside auroral ionosphere. The emission intensity in the whistler-mode band nonmonotonically increased along the satellite trajectory near the plasma jump wall. It has been indicated that waveguides could be formed near the wall during damping of electrostatic oscillations generated by precipitating electron fluxes. A spatially nonmonotonous separation of waveguides from the plasma inhomogeneity stretched along geomagnetic field lines is possible in this case.     

Specific features of resonance structures in spectra of ULF electromagnetic noise at high latitudes (Barentsburg observatory)

Results of studying resonance spectral structures (RSSs) of the noise background in the frequency range 0.1–5 Hz at Barentsburg high-latitude observatory (Spitsbergen) are presented. It has been indicated that the diurnal variations in the observation probability and the long-term variations in the RSS observation cannot be explained by variations in the illumination of the ionosphere by the Sun. Based on an analysis of the magnetic measurements, the conclusion is drawn that a decrease in the RSS registration probability in daytime hours and in winter months are related to an increase in the variability of ionospheric parameters. It has been indicated that the RSS source is located in the region above an observation point, and the horizontal scale of this source is 100–200 km, which agrees with the concepts of the role of the ionospheric Alfvén resonator in the formation of RSS.     

Magnetic field behavior in the magnetosheath when the IMF slightly differs from the solar wind velocity vector

The magnetic field behavior in the magnetosheath, when the IMF and the solar wind velocity are almost collinear, has been analyzed based on the perturbation method. Magnetic disturbances are considered against a background of the stationary MHD solar wind flow around the magnetosphere when the magnetic field and the solar wind velocity are strictly collinear. It has been indicated that the angle between the magnetic field and velocity vectors increases considerably in a relatively thin layer near the magnetopause. The angle rise factor profiles have been determined for different distances from the subsolar point. The thickness of the layer, where the angle reaches values of about unity and more, has been estimated. It is important to take this layer into account when the magnetopause stability with respect to Kelvin-Helmholtz waves is analyzed.     

Geomagnetic field variations induced by internal and surface waves in the four-layer model of the marine environment

The layered model of the marine environment, including the atmosphere, two seawater layers with different conductivity and density, and the bottom rock layer, has been considered. The geomagnetic field variations, generated by internal and surface waves with different frequency and propagation direction, have been found in the scope of this model. The effect of magnetic permeability and electric conductivity of bottom rocks on induced magnetic field has been taken into account. The transfer functions and spectral densities of these variations have been analytically determined and numerically estimated.     

Prediction of the field strength fading forms by means of weather situations

Summary In this study the different forms of the electromagnetic field strength recordings at the Thera-Crete microwave line of link are examined, in comparison with the corresponding weather situations prevailing over that area. According to the amplitude of fluctuations, the different forms of recordings have been classified in three basic typesA, B, C and the annual frequency of the appearance of these types has been observed. Finally, the influence of weather situations on radio wave propagation was examined and it has been found that in most cases a close relationship exists between weather situations and the different fading forms of the electromagnetic field so that a prediction of the fading form be possible by means of the weather forecast.This study was sponsored by a research grant from NATO's Scientific Committee.     

多孔径瞬变电磁场物理模拟

为了提高瞬变电磁法对地探测精度,提出了一种新颖的瞬变电磁装置一多孔径发射装置,并进行了多孔径瞬变电磁场物理模拟观测.分别使用四孔径发射装置和常规回线发射装置,进行不同收一发距情况下的一次场观测,并对铜板在不同埋藏深度情况下的二次响应进行观测,通过比较两种不同装置下的响应曲线和计算观测数据误差,最终发现使用四孔径发射装置可使一次场强度提高34%,可使二次场强度提高31%.结论表明,多孔径发射源可以改变电磁场的空间分布,认为瞬变电磁场存在类相干现象.研究成果对提高瞬变电磁的探测精度具有很重要的意义.