Field-aligned currents and magnetospheric generator in experiments on a laser-produced plasma flowing around a magnetic dipole

A laboratory experiment on modeling the magnetospheric generator of the field-aligned currents and the Earth’s transpolar potential in the absence of IMF is illustrated. The measurements of the total field-aligned current in the generator shorted mode and the transpolar potential in the circuit disconnection mode made it possible to determine the generator internal resistance. A model that explains the saturation current and internal resistance by the feedback between the field-aligned current and plasma flank motions has been proposed. This feedback is described through the effective resistance, which is proportional to the flow rate and the ratio of the boundary layer to the dimension of the magnetosphere. For the experimental conditions, the calculated generator resistance was in good agreement with the measured value. The estimates for the Earth’s magnetosphere indicate that the MHD generator internal resistance in the boundary layer is usually much lower than the reverse integral conductivity of the ionosphere.     

Structure of the Disturbed Magnetosphere

The quasitrapping region (QTR) at the night side of a disturbed magnetosphere in the majority of models is either absent completely or merges with the plasma sheet of the magnetosphere tail. At the same time these two regions are different both in the topology of the magnetic field and in the character of motion of charged particles. Moreover, it is the region of quasitrapping that is conjugate to the zone of auroral active forms; i.e., it can be called the auroral magnetosphere. Models of the magnetosphere in which the tail structures of the magnetic field are directly adjacent to the boundary of stable trapping (in particular, the isotropic boundary model) are based on erroneous assumptions. Our understanding of the processes of magnetosphere substorms and magnetic storms depends on a correct understanding of the magnetosphere structure.     

A Magnetospheric Substorm and the Motion of the Magnetopause

Using a single event as an example, we make an analysis of the time development of a substorm and estimate its influence on the motion of the low-latitude boundary of the magnetosphere. To this end, we compare the data on plasma and magnetic field obtained by five spacecraft (WIND, INTERBALL-1, GEOTAIL, GOES-8, and GOES-9) with measurements made by ground-based stations. It is shown that the release of energy of the geomagnetic tail begins from a disruption of the current sheet near the Earth. The high-speed plasma stream that transfers a magnetic flux to the Earth and can have an effect on the magnetic field configuration near the Earth is detected later. Almost simultaneously with a substorm onset a series of magnetopause crossings has been detected by the INTERBALL-1 satellite on the evening side of the low-latitude magnetosphere. In this paper we consider some of possible causes of this motion of the magnetosphere boundary, including variations of parameters of the solar wind, Kelvin-Helmholtz instability, and substorm processes. It is shown that fast motions of the magnetopause are detected almost simultaneously with field variations in the near magnetotail of the Earth and geomagnetic pulsations Pi2 on ground-based stations. A sufficiently high degree of correlation (K = 0.67) between the amplitude of Pi2 pulsations and the amplitude of magnetic field variations near the magnetopause is probably indicative of the connection of short-term motions of the magnetosphere boundary with the tail current disruption and the process of formation of a substorm current wedge.__________Translated from Kosmicheskie Issledovaniya, Vol. 43, No. 4, 2005, pp. 248–259.Original Russian Text Copyright © 2005 by Nikolaeva, Parkhomov, Borodkova, Klimov, Nozdrachev, Romanov, Yermolaev.     

Low Altitude Cusp–Cleft Region Signatures of Strong Geomagnetic Disturbances

The polar cusp being a region of the free access of the solar wind into the inner magnetosphere is also the site of turbulent plasma flow. The cusp area at low altitudes acts like a focus of a variety type of instability and disturbances from different regions of the Earth. Daily f ₀ F2 frequencies are discussed regarding the cusp position. The high time resolution wave measurements together with electron and ion energetic spectra measurements registered on the board the Freja satellite and Magion-3 and the electron density at the peak of f ₀ F2 layers collected from ground-based ionosonde measurements were used to study the response of ionospheric plasma within the cusp–cleft region to the strong geomagnetic storm. In this paper we present the response of the ionospheric plasma to the disturbed conditions seen in the topside wave measurements and in the ionospheric characteristics maps obtained from the ground-based VI network. The need of the cusp feature model for radio communication purposes is advocated.     

Finding the dispersion of low-frequency waves in cosmic plasma from the results of multi-satellite measurements

An improved method of analysis of low-frequency wave processes in the interplanetary plasma using the results of multi-satellite measurements is presented. The new method develops the phase difference method and is distinguished by the fact that it allows one to analyze wavelengths several times shorter than the mean separation between spacecraft that perform the measurements. Its capabilities and the feasibility of analyzing events in different regions where spacecraft plasma measurements are undertaken are demonstrated using several examples of dispersion functions obtained by this method from the results of processing the magnetic field measurements on four spacecraft of the Cluster mission. The remarkable role played by ion-cyclotron oscillations in the outer magnetosphere cusp region is demonstrated, which manifests itself in wave generation and nonlinear structure formation.     

Pressure balance on the magnetopause near the subsolar point according to observational data of the THEMIS project satellites

An analysis of the pressure balance on the magnetopause near the subsolar point has been made for 18 crossings of the magnetopause by the THEMIS project satellites under magneto-quiet conditions. Dynamic and static pressures of plasma are determined, as well as magnetic pressure in the magnetosheath, and magnetic and plasma static pressure inside the magnetosphere. Variations of the total pressure have been studied in the case when one satellite is located inside the magnetosphere and another one stays in the magnetosheath near the magnetopause. It is demonstrated that for 18 investigated events the condition of pressure balance at the subsolar point is valid on average with an accuracy of 7%, within measurement errors and under applicability of the approximation of anisotropic magnetic hydrodynamics to collisionless plasma of the magnetosheath and magnetosphere.     

Calculation of the Initial Magnetic Field for Mercury’s Magnetosphere Hybrid Model

Several types of numerical models are used to analyze the interactions of the solar wind flow with Mercury’s magnetosphere, including kinetic models that determine magnetic and electric fields based on the spatial distribution of charges and currents, magnetohydrodynamic models that describe plasma as a conductive liquid, and hybrid models that describe ions kinetically in collisionless mode and represent electrons as a massless neutralizing liquid. The structure of resulting solutions is determined not only by the chosen set of equations that govern the behavior of plasma, but also by the initial and boundary conditions; i.e., their effects are not limited to the amount of computational work required to achieve a quasi-stationary solution. In this work, we have proposed using the magnetic field computed by the paraboloid model of Mercury’s magnetosphere as the initial condition for subsequent hybrid modeling. The results of the model have been compared to measurements performed by the Messenger spacecraft during a single crossing of the magnetosheath and the magnetosphere. The selected orbit lies in the terminator plane, which allows us to observe two crossings of the bow shock and the magnetopause. In our calculations, we have defined the initial parameters of the global magnetospheric current systems in a way that allows us to minimize paraboloid magnetic field deviation along the trajectory of the Messenger from the experimental data. We have shown that the optimal initial field parameters include setting the penetration of a partial interplanetary magnetic field into the magnetosphere with a penetration coefficient of 0.2.     

Geocorona of Hot Plasma

This review deals with basic results of experimental and theoretical studies (numerical simulations included) of the distributions, composition, and dynamics of particles of a hot plasma in the geomagnetosphere. Attention is drawn mainly to the ring current and the plasma sheet of the magnetotail, which play a key role in physics of the magnetosphere. The integrity (unity) of the system outer radiation belt–ring current–near plasma sheet is substantiated (the concept of a hot plasma geocorona). From the viewpoint of this concept, the physical processes and theories are considered that were suggested in order to explain the structure and dynamics of the hot magnetosphere plasma. An emphasis is made on disputable issues and topical problems so far unsolved.     

Distribution of Plasma Pressure in the Geomagnetic Tail in the Transition Region from Dipole to Quasidipole and Stretched Magnetic Field Lines: Events on October 13, 1995 and March 13, 1996

The results of an analysis of the pressure distribution of the hot magnetosphere plasma and transverse currents in the plasma at distances from 8R _E to 12R _E are presented. The data were taken in the vicinity of the equatorial plane onboard the Interball-1 satellite during its passages on October 13, 1995 and March 13, 1996. The pressure was determined from the measurements of particle fluxes by the CORALL, DOK-2, and SKA-2 instruments. The specific features of this experiment made it possible to calculate the pressure with a high accuracy and to determine the distribution of the magnetostatically equilibrium currents in the plasma. It is shown that at the parts of the monotonous increase of the pressure in the earthward direction one can detect regions of plateau in the plasma pressure. A possible origin of the small-scale variations and regions with plateau are discussed. A comparison of the measured pressure profiles with the pressure profiles in the Tsyganenko and Mukai-2003 model is performed. Transverse currents flowing in the plasma are calculated assuming magnetostatic equilibrium.     

The Earth's Magnetosphere Response to Solar Wind Events according to the INTERBALL Project Data

The results of studying the interaction of two types of the solar wind (magnetic clouds and solar wind of extremely low density) with the Earth's magnetosphere are discussed. This study is based of the INTERBALL space project measurements and on the other ground-based and space observations. For moderate variations of the solar wind and interplanetary magnetic field (IMF) parameters, the response of the magnetosphere is similar to its response to similar changes in the absence of magnetic clouds and depends on a previous history of IMF variations. Extremely large density variations on the interplanetary shocks, and on leading and trailing edges of the clouds result in a strong deformation of the magnetosphere, in large-scale motion of the geomagnetic tail, and in the development of magnetic substorms and storms. The important consequences of these processes are: (1) the observation of regions of the magnetosphere and its boundaries at great distances from the average location; (2) density and temperature variations in the outer regions of the magnetosphere; (3) multiple crossings of geomagnetic tail boundaries by a satellite; and (4) bursty fluxes of electrons and ions in the magnetotail, auroral region, and the polar cap. Several polar activations and substorms can develop during a single magnetic cloud arrival; a greater number of these events are accompanied, as a rule, by the development of a stronger magnetic storm. A gradual, but very strong, decrease of the solar wind density on May 10–12, 1999, did not cause noticeable change of geomagnetic indices, though it resulted in considerable expansion of the magnetosphere.     

The development of compression long-period pulsations on the recovery phase of the magnetic storm on May 23, 2007

The features of the excitation of spatially localized long-period (10–15 min) irregular pulsations with a maximum amplitude of ~200 nT at a geomagnetic latitude of 66° in the morning sector 5 MLT are considered. Fluctuations were recorded against the background of substorm disturbances (maximum AE ~ 1278 nT). Antiphase variations of plasma density and magnetic field accompanied by vortex disturbances of the magnetic field both in the magnetosphere and the ionosphere have been recorded in the magnetosphere in this sector. Compression fluctuations corresponding to a slow magnetosonic wave have been recorded in the interplanetary medium in the analyzed period. It is assumed that pulsations have been excited in the localization of the cloud of injected particles in the plasma sheet by compression fluctuations caused by variations of the dynamic pressure of solar wind.     

Vertical structure of the magnetic field in active regions of the sun at coronal heights

High-altitude measurements and magnetic field distribution in active regions are always an important problem to verify existing models at heights from units to hundreds of Mm. Optical methods of analysis of the magnetic structure work well only at the photosphere level. At the same time, the progress of radio astronomy methods of analyzing the solar radio emission [1] and of the theory of solar plasma radiation [2] facilitates introduction of new methods for measuring the magnetic field strength at various altitudes in the solar atmosphere. In this paper we use multi-wave observations of polarization of the radio emission of active regions in the microwave range together with precise magnetosphere data in order to develop a method of projection for measuring the height distribution of the magnetic field.     

On the dynamics of latitudinal profiles of low-energy solar protons in the Earth magnetosphere

Many works have been devoted to studying the boundaries of the penetration of solar protons into the Earth’s magnetosphere. This work first considers the dynamics of not only the boundary, but the latitudinal profiles of penetration in general depending on the energy and local time of measurement according to the data of the low-altitude CORONAS-F satellite. When flying through the polar cap, the isotropic pitchangle distribution of protons leads to the equality of the recorded precipitating flux and the proton flux in the interplanetary space. Beginning at a particular latitude, the proton flux begins to drop and, over time, reaches the level of the background of galactic cosmic rays. The latitudinal profile measured in this manner on the night side reaches the bending point when the Larmor radius of the proton becomes comparable with the radius of the curvature of the line of force; after partial trapping, the flux of precipitating protons successively drops. The protons are transferred to the day side by the magnetic drift and, unlike the night profile, the character of the day profile depends on the configuration of the entire magnetosphere. The character of latitudinal profiles has been studied depending on the local time and energy of the particles, which enabled the features of the magnetosphere deformation to be evaluated at certain times of magnetic storms.     

Radial propagation velocity of energetic particle injections according to measurements onboard the <Emphasis Type="Italic">Cluster</Emphasis> satellites

Injections of energetic electrons with a dispersion over energies were observed during the February 23, 2004 (at about 03:20 UT) substorm onboard the Cluster satellites in the vicinity of perigee near the midnight meridian. The delays in the particle observation caused by the energy dependence of the magnetic drift velocities made it possible to determine the position and time of the beginning of the drift, tracing the trajectories of the leading center of particles back in time in the magnetospheric model. The comparisons of the measurements of four satellites allowed us to determine the radial propagation of the injection front with a velocity of 100–150 km/s at a distance of 7–9 R _E. The comparison with a few previous measurements shows a substantial slowing down of injections as they approached the Earth, and this confirms the prospects of this method for more detailed study of propagation of plasma injection into the inner magnetosphere.     

Verification of the Accuracy of the Magnetopause Empirical Models Using the INTERBALL-1 Satellite Data

A statistical analysis of the shape and location of the magnetopause according to the INTERBALL-1 satellite data for the period 1995–1997 is carried out. The instants of crossing the magnetosphere boundaries obtained by the plasma and magnetic data are compared with computations based on three empirical models, namely, Petrinec and Russel, 1996; Shue et al., 1997; and Shue et al., 1998. The state of the interplanetary medium (dynamic pressure of the solar wind plasma P _d and the B _z component of the interplanetary magnetic field) was determined by the measurements onboard the WIND spacecraft. We estimate the accuracy of the considered models for different groups of boundary crossings: single, multiple with small duration (less than 40 min), and multiple with large duration (more than 40 min). It is demonstrated that the small-scale motions of the boundary (<1R _E) are observed more often in the dayside magnetosphere, especially near the cusp region. Large-scale boundary oscillations (>1R _E) are more common in the tail region of the magnetosphere, namely, its flanks. Various models give similar results: about 50% of all events have deviations by more than 1R _E from the model locations. In some cases, the deviation of the measured location of the magnetosphere boundary from the model prediction may be as large as 5–6R _E for all three models considered, the actual boundary being more often located nearer to the Earth than the result of model computations. The best model is that of Shue et al., 1998, but it does not differ significantly from the other models.     

The effect of heavy ions on the spectrum of oscillations of the magnetosphere

Some issues concerning the influence of multi-ion composition of plasma on the spectrum of ultralow frequency (ULF) oscillations in the magnetosphere are analyzed. Main emphasis is made on the effects that are perceptible by analyzing the results of observations of ULF oscillations. The resonator confining ion cyclotron waves in the equatorial zone high above the Earth is considered, as well as the near-equatorial waveguide existing under the plasmasphere arch and canalizing magnetosonic waves in the azimuth direction. It is shown that the very existence of the ion-cyclotron resonator would be impossible, if only one species of ions were contained in plasma. It is emphasized that the problem of excitation of magnetosonic waves with harmonics of the gyrofrequency of O⁺ needs further investigation. The effect of heavy ions on the spectrum of Alfvén oscillations of the magnetosphere is considered. Some arguments are presented giving evidence that existence of alpha-particles in the solar wind leads to an asymmetry of the spectrum of magnetosonic oscillations in front of the Earth’s bow shock. Anomalously large asymmetry is expected at immersion of the Earth into the “plasmasphere” of the flare-associated stream of solar plasma. The general conclusion is made that even a small admixture of heavy ions can have a substantial effect on the spectrum of ULF oscillations.     

Study of the magnetospheres of active regions on the sun by radio astronomy techniques

In the 1990s, based on detailed studies of the structure of active regions (AR), the concept of the magnetosphere of the active region was proposed. This includes almost all known structures presented in the active region, ranging from the radio granulation up to noise storms, the radiation of which manifests on the radio waves. The magnetosphere concept, which, from a common point of view, considers the manifestations of the radio emission of the active region as a single active complex, allows one to shed light on the relation between stable and active processes and their interrelations. It is especially important to identify the basic ways of transforming nonthermal energy into thermal energy. A dominant role in all processes is attributed to the magnetic field, the measurement of which on the coronal levels can be performed by radio-astronomical techniques. The extension of the wavelength range and the introduction of new tools and advanced modeling capabilities makes it possible to analyze the physical properties of plasma structures in the AR magnetosphere and to evaluate the coronal magnetic fields at the levels of the chromosphere–corona transition zone and the lower corona. The features and characteristics of the transition region from the S component to the B component have been estimated.     

Plasma flow disturbances in the magnetospheric plasma sheet during substorm activations

We have considered variations in fields and particle fluxes in the near-Earth plasma sheet on the THEMIS-D satellite together with the auroral dynamics in the satellite-conjugate ionospheric part during two substorm activations on December 19, 2014 with K _p = 2. The satellite was at ~8.5R_E and MLT = 21.8 in the outer region of captured energetic particles with isotropic ion fluxes near the convection boundary of electrons with an energy of ~10 keV. During substorm activations, the satellite recorded energetic particle injections and magnetic field oscillations with a period of ~90 s. In the satellite-conjugate ionospheric part, the activations were preceded by wavelike disturbances of auroral brightness along the southern azimuthal arc. In the expansion phase of activations, large-scale vortex structures appeared in the structure of auroras. The sudden enhancements of auroral activity (brightening of arcs, auroral breakup, and appearance of NS forms) coincided with moments of local magnetic field dipolarization and an increase in the amplitude Pi2 of pulsations of the B_z component of the magnetic field on the satellite. Approximately 30–50 s before these moments, the magnetosphere was characterized by an increased rate of plasma flow in the radial direction, which initiated the formation of plasma vortices. The auroral activation delays relative to the times when plasma vortices appear in the magnetosphere decreased with decreasing latitude of the satellite projection. The plasma vortices in the magnetosphere are assumed to be responsible for the observed auroral vortex structures and the manifestation of the hybrid vortex instability (or shear flow ballooning instability) that develops in the equatorial magnetospheric plane in the presence of a shear plasma flow in the region of strong pressure gradients in the Earthward direction.     

Radiative Electrification of Spacecraft Construction Elements: Physical Modeling of Charge Accumulation and Neutralization

The basic principles of physical modeling of spacecraft radiative electrification in the ionosphere and the magnetosphere are formulated. It is shown that recorded cyclograms and current pulses of discharges provide complete information on the electrophysical properties of materials. The efficiency of plasma neutralization of electro-radiative effects depends on the density of low temperature plasma and the structure of the irradiated surface.     

Features of whistling electromagnetic wave propagation descending from above upon the night ionosphere

The results of numerical solution of the wave equations for the oblique incidence of whistling electromagnetic waves upon the night ionosphere from above have been obtained and analyzed. In the studied region of altitudes, within the wavelength scale, charged particle concentration varies drastically, and damping caused by collisions between the charged and neutral particles decreases considerably. Below, the sharp lower boundary of the ionosphere, the refractive index of the whistler wave approaches unity, and plasma turbulence transform into atmospheric electromagnetic waves. The dependences of the whistler reflection factor are found in terms of energy and horizontal magnetic component of the electromagnetic wave near the Earth’s surface on the frequency and the wave vector transverse component for the plain-layered medium model at two values of latitude. Strong dependences have been found on the wave angle of incidence and frequency. At rather small angles of incidence, the wave disturbances reach the Earth’s surface, and the module of reflection coefficient logarithm is in the range of 0.4–1. At large angles of incidence, the reflection coefficient module varies over a wide range depending on specific conditions. The obtained results explain the absence of oscillation modes of plasma magnetosphere maser in the night magnetosphere.