Generation of magnetic field Pc5 pulsations and particle fluxes during the recovery phase of a magnetic storm on October 31, 2003

The spatial structure of intensive Pc5 pulsations of the geomagnetic field and riometer absorption during the recovery phase of a strong magnetic storm that occurred on October 31, 2003, have been considered in detail. The global structure of disturbances has been analyzed based on a global network of magnetometers and riometers supplemented by the data of magnotometers and particle detectors on geostationary satellites GOES and LANL. The local spatial structure was studied by the data of a regional network of Finland vertical riometers and the stations at the IMAGE magnetic network. Quasiperiodic variations in the magnetic field and riometer absorption are generally similar and have a close frequency composition; nevertheless, their local spatial structures are different, as a result of which the concept that riometer absorption pulsations represent a purely modulation process is doubtful. It is assumed that the observed variations are oscillations of two related systems: the magnetospheric MHD waveguide/resonator and systems including cyclotron noise and electrons. Geomagnetic Pc5 oscillations during the recovery phase of a strong magnetic storm supposedly result from the generation of the magnetospheric waveguide on magnetospheric flanks. An analysis of azimuthal propagation phase velocities indicates that these oscillations depend on intramagnetospheric parameters rather than on the solar wind velocity. The magnetospheric waveguide is in a metastable state when solar wind velocities are high, and the quasiperiodic fluctuations of the solar wind pressure stimulate the excitation of the waveguide.     

Contribution of global Pc5 oscillations to magnetic disturbance during geomagnetic storms

The contribution of global magnetospheric oscillations to magnetic disturbance during magnetospheric storms is studied. The bases of magnetic data from the INTERMAGNET global network in combination with the interplanetary and intramagnetospheric measurements of the magnetic field and plasma and the sets of the Kp, Dst, and AE indices are used for this purpose. The most favorable conditions in the solar wind and magnetosphere for generation of global Pc5 have been revealed. The contribution of these oscillations to the variations in the magnetic disturbance level, characterized by the AE index, has been estimated. The findings confirm that magnetospheric MHD oscillations participate in the processes of energy income from the solar wind and energy dissipation in the magnetosphere.     

Upward acceleration of magnetospheric ions by oscillatory centrifugal force

The paper addresses the issue of upward acceleration of ions along geomagnetic field lines. It has been shown that ion acceleration by electric field oscillations (formerly known as magnetic moment “pumping” or MMP) may be treated as a centrifugal acceleration mechanism. More precisely, the case in point is oscillatory centrifugal acceleration; this brings up the question on comparing the MMP with the centrifugal acceleration caused by the quasi-static magnetospheric convection field. It has been found that at high geomagnetic latitudes, the oscillatory centrifugal force is weaker or stronger than the centrifugal force of magnetospheric convection if the ratio of the electric field oscillation amplitude to the mean field is correspondingly lower or higher than \(\sqrt 2 \). Analysis of data from measurements and calculations of magnetospheric electric fields suggests that, contrary to current opinion, the oscillatory centrifugal force may be comparable to the centrifugal force of magnetospheric convection and even exceed it when strong global Pc5 pulsations are excited in the magnetosphere.     

Precipitation of energetic magnetospheric electrons and accompanying solar wind characteristics

From 1957 up to the present time, the Lebedev Physical Institute (LPI) has performed regular monitoring of ionizing radiation in the Earth’s atmosphere. There are cases when the X-ray radiation generated by energetic magnetospheric electrons penetrates the atmosphere and is observed at polar latitudes. The vast majority of these events occurs against the background of high-velocity solar wind streams, while magnetospheric perturbations related to interplanetary coronal mass ejections (ICMEs) are noneffective for precipitation. It is shown in the paper that ICMEs do not cause acceleration of a sufficient amount of electrons in the magnetosphere. Favorable conditions for acceleration and subsequent scattering of electrons into the loss cone are created by magnetic storms with an extended recovery phase and with sufficiently frequent periods of negative Bz component of the interplanetary magnetic field (IMF). Such geomagnetic perturbations are typical for storms associated with high-velocity solar wind streams.     

Injection of relativistic electrons into the internal magnetosphere during magnetic storms: Connection with substorms

The connection between rapid increases in the intensity of electrons with energies >0.3 MeV and magnetospheric substorms was studied for the first time by measurements of energetic electrons on the low-orbit SERVIS-1 satellite. In addition to the well-known process of radial diffusion detected at the recovery phase, the increases during a period of time no longer than 1.5 h at the main phase of six magnetic storms in a channel of 0.3–1.7 MeV (in three of them, in a channel of 1.7–3.4 MeV) were measured. An analysis of auroral zone magnetograms demonstrated that the increases occurred at the instant of magnetospheric substorm activation. A conclusion is made that the increases are caused by the radial injection of electrons by a pulse electric field induced during substorm activations. Pulse injections are shown to be one of the main mechanisms of electron radiation belt completion in the inner magnetosphere and, in combination with moderate radial diffusion, to be responsible for the appearance of large fluxes of energetic electrons (“killers”) in the magnetosphere after magnetic storms.     

Quasi-periodic precipitation with periods between 40 and 60 minutes

Intervals of periodic enhancements of E-region electron density have been found in EISCAT (European Incoherent SCATter) data. The periods are typically between 40 and 60 min. The phenomenon is observed during relatively quiet times, though after geomagnetic disturbances; it may last up to 6 h. The events can occur at all times of day with a maximum probability in the MLT morning sector. Using the EISCAT database from recent years, the statistical characteristics of these events, and their relation to magnetospheric conditions defined by the Dst index and the d.c. electric field perpendicular to B\= have been derived. The latitudinal extent is found to be several degrees, but the longitudinal extent is not known. It is concluded that these events are due to the periodically modulated flux of electron precipitation controlled by oscillations in the magnetospheric tail.     

电离层人工调制激发的VLF波在磁层的传播特性及应用研究

电离层人工调制可以激发甚低频（VLF）波,其中向上传播进入磁层的VLF波,不但能够用来研究磁层中的各种物理现象,且具有人工沉降高能粒子,消除辐射带等实际用途.本文使用射线追踪方法,模拟电离层调制激发的VLF波在磁层的传播路径,分析激发纬度和调制频率对传播路径和传播特性的影响;并基于低频波的色散方程和波粒共振条件,分析VLF波传播路径上与磁层高能粒子的最低共振能及其分布.研究表明,VLF波通过在磁层来回反射向更高的L-shell传播,最终稳定在某一L-shell附近.以较低的调制频率或者从较高的纬度激发的VLF波能够传播到更高的L-shell,但是,当激发纬度过高时,低频波也可能不发生磁层反射而直接进入电离层和大气层.低频波在磁层的传播过程中,在较高的纬度或者较低的L-shell能够与较高能量的电子发生共振相互作用,在较高的L-shell并且低纬地区,能够与较低能量的电子发生共振相互作用.共振谐数越高,能发生波粒共振的电子能量越高.     

Numerical modeling of the behavior of super-small-scale irregularities in the ionospheric <Emphasis Type="Italic">F</Emphasis>2 layer

Using a mathematical modeling method, evolutions of super-small-scale irregularities of electron concentration stretched along the geomagnetic field which could be formed in the magnetized ionospheric plasma of the F2 layer both in a natural way and at an artificial impact on it, in particular, during heating experiments, are studied. Evolution in time of the initially formed irregularities of two types having different shape of the cross sections lateral to the magnetic field (types of direct narrow long band and with a circular cross section) is calculated. It is found that such irregularities during times tens of times shorter than the time of the electron free path time spread out and disappear, accomplishing thereby periodic attenuating oscillations. The period of these oscillations can be equal to both the period of Langmuir oscillations of electrons and the period of cyclotron oscillations of electrons depending on the irregularity type and its initial parameters.     

Impact of Different Types of Interplanetary Medium Disturbances of High-Energy Electrons on the Geostationary Orbit

Geomagnetism and Aeronomy - Specific features of the behavior of streams of relativistic magnetospheric electrons at energies higher than 2 MeV on geostationary orbits during different types of...     

Range finding of Alfvén oscillations and direction finding of ion-cyclotron waves by using the ground-based ULF finder

A new approach to the problem of direction and distance finding of magnetospheric ULF oscillations is described. It is based on additional information about the structure of geoelectromagnetic field at the Earths surface which is contained in the known relations of the theory of magnetovariation and magnetotelluric sounding. This allows us to widen the range of diagnostic tools by using observations of Alfvén oscillations in the PC 3–5 frequency band and the ion-cyclotron waves in the PC 1 frequency band. Preliminary results of the remote sensing of the magnetosphere at low-latitudes using the MHD ranger technique are presented. The prospects for remote sensing of the plasmapause position are discussed.     

Variations in planetary radiation belt fluxes and their radiative observations

The variations in the fluxes of the relativistic electrons in the planetary radiation belts are due to a set of different physical processes which violate one or more of the adiabatic invariants. We survey the mechanisms which break down these invariants and investigate the time scales for the processes and the resulting effects on the observed fluxes. The mechanisms include (a) sudden deformation of the magnetic field configuration, (b) radial diffusion due to low-frequency electromagnetic oscillations, (c) transit-time damping due to fast waves and (d) diffusion due to electromagnetic ion-cyclotron (emic) or whistler waves. It is indicated how the waves which interact resonantly with the relativistic electrons are responsible for enhancement in the radiative spectra of the gyrosynchrotron emissions in the GHz frequency range and the X-ray bremsstrahlung emissions at the MeV energy range.     

Diagnostics of the magnetosphere based on the outer belt relativistic electrons and penetration of solar protons: A review

The present-day state of the studies of the outer radiation belt relativistic electrons and the boundary of the solar proton penetration into the magnetosphere during magnetic storms is briefly reviewed. The main attention is paid to the results from studying the interrelation between these structural formations and other magnetospheric plasma structures. It has been indicated that the relationship between the position of the maximum of belt of relativistic electrons injected during magnetic storms (L _max) and the magnetic storm amplitude (|Dst|_max = 2.75 × 10⁴/L _max⁴) can be used to predict the extreme latitudinal position of such magnetospheric plasma formations as a trapped radiation region boundary, the nighttime equatorial boundary of the auroral oval, and westward electrojet center during a storm. Using the examples of still rare studies of the solar proton boundary dynamics in the magnetosphere based on the simultaneous measurements on several polar satellites, it has been demonstrated that a change in the geomagnetic field topology during magnetic storms can be diagnosed.     

Weimer电场模式在地球磁层内的特征

地球磁层中的电场是研究磁层物理的重要参数,目前常用的对流电场有均匀晨昏电场和投影电场.电离层电场可以看做磁层电场沿磁力线在电离层的投影,本文选取的电离层电场模型为Weimer(2001模式)电场.利用T96磁场模式,沿磁力线将电离层电场投影到磁层空间,得到一个新的磁层电场模式,并讨论了磁暴、行星际磁场(IMF)、太阳风参数和亚暴等对磁层电场的影响.利用该模型计算的电场结果与卫星探测结果相符.     

Large-scale LF electromagnetic waves in the Earth’s magnetosheath

The model equations describing the dynamics of the solar wind and interplanetary magnetic field in the dayside Earth’s magnetosheath have been studied. The large-scale flow structure near the critical point of the magnetosphere is determined in an approximation of the Chaplygin stagnation zone identified with the magnetosheath focal part. It has been indicated that magnetic gradient waves (MGWs), which represent a special branch of ULF electromagnetic oscillations of the magnetospheric resonator, can be generated in a magnetized plasma in the case when the magnetic field distribution is spatially inhomogeneous. The characteristic frequencies, periods, phase velocities, wavelengths, and amplitudes of MGW magnetic pulsations have been determined.     

Energetic Particles Observed in the CUSP Region During a Storm Recovery Phase

In this paper we report energetic ion behavior and its composition variations observed by the Cluster/RAPID instrument when the spacecraft was travelling in the high latitude magnetospheric boundary region on the day of the 31 March, 2001, strongest magnetic storm in the past 50 years. The Dst index reached −360 nT at about 09:00 UT. During its early recovery phase, large amounts of oxygen and helium ions were observed; the ratio of oxygen to hydrogen in the RAPID energy range reached as high as 250%, which suggests that the observed energetic particles might be of magnetospheric origin. The observations further show that enhanced energetic electron fluxes are confined in a very narrow region, while protons have occupied a larger region, and heavy ions have been observed in an even larger region. The flux of energetic electrons show a slight enhancement in a region where the magnetic field magnitude is around zero. These observed energetic ions could be quasi-trapped by the current sheet in the stagnation region of the cusp.     

Resonant enhancement of relativistic electron fluxes during geomagnetically active periods

The strong increase in the flux of relativistic electrons during the recovery phase of magnetic storms and during other active periods is investigated with the help of Hamiltonian formalism and simulations of test electrons which interact with whistler waves. The intensity of the whistler waves is enhanced significantly due to injection of 10–100 keV electrons during the substorm. Electrons which drift in the gradient and curvature of the magnetic field generate the rising tones of VLF whistler chorus. The seed population of relativistic electrons which bounce along the inhomogeneous magnetic field, interacts resonantly with the whistler waves. Whistler wave propagating obliquely to the magnetic field can interact with energetic electrons through Landau, cyclotron, and higher harmonic resonant interactions when the Doppler-shifted wave frequency equals any (positive or negative) integer multiple of the local relativistic gyrofrequency. Because the gyroradius of a relativistic electron may be the order of or greater than the perpendicular wavelength, numerous cyclotron, harmonics can contribute to the resonant interaction which breaks down the adiabatic invariant. A similar process diffuses the pitch angle leading to electron precipitation. The irreversible changes in the adiabatic invariant depend on the relative phase between the wave and the electron, and successive resonant interactions result in electrons undergoing a random walk in energy and pitch angle. This resonant process may contribute to the 10–100 fold increase of the relativistic electron flux in the outer radiation belt, and constitute an interesting relation between substorm-generated waves and enhancements in fluxes of relativistic electrons during geomagnetic storms and other active periods.     

The contribution of magnetospheric currents toSq

Since the discovery of the magnetosphere, it has been known that the currents flowing in the magnetosphere contribute toSq, the regular daily variation in the earth's surface magnetic field. The early models, however, were not very accurate in the vicinity of the earth. The magnetospheric contribution toSq has therefore been recalculated by direct integration over the three major magnetospheric current systems; magnetopause, tail and ring. The finite electrical conductivity of the earth, which increases the horizontal and decreases the vertical components of the magnetospheric field at the earth's surface, has been taken into account. The magnetospheric currents are found to contribute 12 nanotesla to the day to night difference in the mid-latitudeSq pattern for steady, quiet magnetospheric conditions. They also contribute to the annual variation in the surface field and must be considered an important source of the observed day to day variation in theSq pattern.     

Effect of magnetic storms in variations in the atmospheric electric field at midlatitudes

The observations of the variations in the vertical component of the atmospheric electric field (E _z ) at Swider midlatitude Poland observatory (geomagnetic latitude 47.8°) under the conditions of fair weather during 14 magnetic storms have been analyzed. The effect of the magnetic storm main phase in the daytime midlatitude variations in E _z in the absence of local geomagnetic disturbances has been detected for the first time. Considerable (～100–300 V m^?1) decreases in the electric field strength (E _z ) at Swider observatory were observed in daytime simultaneously with the substorm onset in the nighttime sector of auroral latitudes (College observatory). The detected effects indicate that an intensification of the interplanetary electric field during the magnetic storm main phase, the development of magnetospheric substorms, and precipitation of energetic electrons into the nighttime auroral ionosphere can result in considerable disturbances in the midlatitude atmospheric electric field.     

A determination of the hydromagnetic waves polarization from their perturbations on the terminator

The influence of the homogeneous and inhomogeneous ionosphere on the orientation angle of the horizontal magnetic vectors of the long-time geomagnetic pulsations is under consideration in this study. It was realized that this angle is small in the case of the homogeneous ionosphere for both the Alfvén and magnetosonic types of oscillations. An increase in the ionospheric electric field was discovered as the ionospheric conductivity changes during the switch from day to night conditions. It is valid only for the initial Alfvén wave. The ionospheric equivalent current systems excited by the initial magnetospheric waves of Alfvén and magnetosonic types as well as their behavior near the terminator were studied for different seasons. For the Alfvén source, seasonal variations of the orientation angle close to sunrise at the equator depend on the type of source: odd or even modes of Alfvén oscillations excite observable pulsations. It was found that the ionospheric two-vortex equivalent current system of the long-period pulsations arising in high-latitudes in the equatorial region alters not only its direction, but its intensity too. The largest anomaly (\sim25% of the source value) would be expected near the terminator. A new experimental method was suggested to recognize the type of incident magnetospheric waves by implementing observations either at a single observatory or at a couple of observatories. In the case of a single observatory it is proposed to study the frequency dependence of the orientation angle of their magnetic components close to sunrise. If the initial wave is magnetosonic, this angle must not be changed as a function of the local time within the wide frequency range of pulsations. When pulsations have an orientation angle sensitive to the presence of the terminator, they may be classified as both Alfvén and magnetosonic. For the Alfvén waves no frequency dependence of the orientational angle is peculiar. On the contrary, magnetosonic waves should be determined as oscillations with an orientational angle proportional to the frequency. These oscillations may be revealed at observatories located on the high-resistance cross sections. The example of the spectral-temporal analysis of pulsation at the equatorial observatory in Huancayo was demonstrated to confirm the proposed experimental technique. A weak dependence of the orientation angle anomaly on the frequency near the terminator was found. The latter is evidence for the dominant contribution of the Alfvén waves to low-latitude and equatorial oscillations.