Variations of the magnetopause position versus the level of geomagnetic activity (according to data of the INTERBALL-1 Satellite for 1995–1997)

The variations in the deviation of the observed position of the magnetosphere boundary from its mean position predicted by the Shue at al., 1997 (Sh97) model [7] are studied as a function of the substorm activity level (the AE-index value) and magnetic storm intensity (the value of the corrected D _st ^* index). The results obtained make it possible to state that the amplitude of motion of the magnetospheric boundary on the dayside and in the low-latitude tail is small. It is likely that the position of the boundary is either independent of the AE and D _st ^* indices or this dependence is weak. At the same time, the boundary of the high-latitude tail shifts inward on the average by 1.5R _E with an increase of the AE-index in the case of absence of magnetic storms (contraction of the magnetospheric tail). On the contrary, in the presence of magnetic storms, this boundary shifts outward by up to 3R _E with an increase of the AE-index (inflation of the magnetospheric tail). It is also shown that the boundary of the high-latitude tail moves outward with an increase of the D _st ^* index, both at low substorm activity and in periods of high substorm activity. The amplitude of the outward motion of the high-latitude tail of the magnetosphere is by a factor of two higher for moderate magnetic storms with strong substorms than for moderate magnetic storms with weak substorms.     

Geosynchronous magnetopause crossings on October 29–31, 2003

During the period October 29–31, 2003, geosynchronous magnetopause crossings (GMC) have been identified based on the magnetic data of the GOES series spacecraft and plasma data of the LANL series spacecraft. It is shown that most of the time the size of the dayside magnetosphere was highly decreased under the effect of very high pressure associated with high velocities and densities of the solar wind plasma, as well as high negative values of the B_z component of the interplanetary magnetic field (IMF). For tens of hours the subsolar magnetopause was deep inside the geosynchronous orbit. During the main phase and at the maximum of the strong geomagnetic storms that occurred in the period under consideration, the dayside magnetosphere was characterized by a strong dawn-dusk asymmetry, so that its size in the postnoon sector considerably exceeded the size in the pre-noon sector. The geomagnetic disturbances in the morning on October 30 and 31, 2003 were accompanied by global magnetospheric pulsations with periods of 5–10 min and high amplitude (up to 0.8 R_E).Translated from Kosmicheskie Issledovaniya, Vol. 42, No. 6, 2004, pp. 574–584.Original Russian Text Copyright © 2004 by Dmitriev, Suvorova.     

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.     

Observation of the Near Plasma Sheet,Ring Current,and Energetic Electrons from Radiation Belts at a Geosynchronous Orbit,March 11–25, 1992

The dynamics of near plasma sheet electrons and ions (E 0.1–12.4 keV), ring current protons (E _i 41–133 keV), and energetic electrons from the Earth's radiation belts (E _e 97–1010 keV) is considered using the data from the Gorizont-34and Gorizont-35geosynchronous satellites from March 11–25, 1992. Peculiarities of this period are a long (more than 4 days) interval of the northward interplanetary magnetic field (B _z> 0) and a high-speed stream of the solar wind with an enhanced particle density. The SC and compression of the magnetosphere to the geosynchronous orbit (GMC) preceded this interval. Under quiet and moderately disturbed geomagnetic conditions and under a prolonged northward interplanetary magnetic field, we observed a significant decrease of fluxes and softening of spectra of the electron component of plasma in the energy ranges of 0.1–12.4 keV and 97–1010 keV, and of the ion component of plasma at energies of 0.1–4 keV, while the intensity of 5–12.4 keV ion fluxes increases by about one order of magnitude. The peculiarities of distributions of energetic particle fluxes observed in the period under consideration can be associated with significant variations of the convection conditions and a decreased or fully suppressed injection of energetic electrons into the geosynchronous orbit region.     

On the Origin of High-Latitude Boundary Layer of the Earth's Magnetosphere

Localization of the reconnection region at the dayside magnetopause is among the unsolved problems of magnetospheric physics. There are two alternative models, one of which predicts the reconnection at the equatorial magnetopause, and the other predicts the reconnection in the region where the magnetic field of the solar wind flowing around the magnetosphere is antiparallel to the geomagnetic field. The statistical analysis carried out for 53 INTERBALL-1crossings of the high-latitude magnetopause in a special coordinate frame invariant with respect to the interplanetary conditions shows that the model of a reconnection in antiparallel fields agrees well with the experimental data.     

Some features of solar cosmic ray penetration into the Earth’s magnetosphere

We compared fluxes of the 1–100 MeV solar energetic particles (SEP) measured in the interplanetary medium (ACE) and in the magnetosphere (Universitetsky-Tatiana, POES—in polar caps, and GOES-11—at geosynchronous orbit) during several SEP events of 2005–2006. Peak intensities of the SEP fluxes inside and outside the magnetosphere were compared for each event. It is shown that observed inside-outside difference depends mainly on direction of interplanetary magnetic field (IMF), on degree of the SEP anisotropy (pitch-angle distribution) in IMF, and on distance of the dayside magnetopause from the Earth.     

Estimation of the current density and analysis of the geometry of the current system surrounding the Earth

The results of an investigation of the distribution of plasma pressure, pressure gradients, and magnetic field near the equatorial plane in the plasma ring surrounding the Earth under magneto-quiet conditions are presented. Observational data obtained during the international THEMIS mission are used. The picture of the distribution of transverse-current density near the equatorial plane was obtained under assumption of observing the magnetostatic balance condition at geocentric distances from 6 to 12R _E. In estimating the integral transverse current it was accepted that in daytime sector the magnetic-field minima on magnetic field lines are not localized in the equatorial plane. Estimates of the integral transverse current were obtained, which demonstrate the possibility of closing nighttime transverse currents at geocentric distances of up to ～12R _E inside the magnetosphere, which form a high-latitudinal continuation of the ring current.     

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.     

The Fields of Magnetospheric Current Systems on the Earth's Surface in an Interval of the Magnetic Storm Studied under the International Program on Solar–Terrestrial Physics

Using the magnetic storm in January 1997 as an example, we examined the possibilities to employ the magnetospheric field T96 [1, 2] and the dynamic paraboloid model PM of the magnetosphere [3] for modeling the D _st variation. We have revealed the necessity to refine the results of normalizing the free parameters of the model T96 according to the solar wind parameters. The contributions to the D _st variation of magnetic fields of basic large-scale magnetospheric current systems (the field DCF on the magnetopause, the field DR of the ring current, and the field DT in the magnetotail) are estimated for different phases of the storm from model calculations. Possible causes of a discrepancy between the results of modeling D _st using the T96 and PM models are discussed. Special emphasis is made on the ratios of contributions into the D _st variation of the fields of the magnetotail and the ring current in the main phase of magnetic storms and on the contributions to D _st of the fields of various current systems at the recovery phase.     

Penetration of solar cosmic rays into the Earth’s magnetosphere on January 28, 2012

Results of the comparative analysis of the dynamics of SCR fluxes with energies of 1–100 MeV in the interplanetary environment according to the data of the ACE and Wind spacecraft and within the Earth’s magnetosphere according to the data of the GOES-15 and Electro-L satellites in the region of geostationary orbits, and POES-19 and Meteor-M1 in the region of polar caps during two increases in SCR of January 19–31, 2012, are presented. It is shown that the decrease in the efficiency of SCR penetration into the Earth’s magnetosphere in the region of the orbits under study on January 28, 2012, is related to the passage of the Earth’s magnetosphere through the interplanetary environment structure with a quasi-radial interplanetary magnetic field and a small pressure of the solar wind.     

Reflection Model as Applied for the Analysis of Enhancements of Solar Cosmic Rays at Different Heliocentric Distances: An Example of the Event Observed in June 1991 onboard GRANAT and ULYSSES Spacecraft

In this paper we consider a large-scale enhancement of the intensity of solar protons (E = 1–20 MeV) observed in June 1991 for 26 days at different points of interplanetary space, onboard ULYSSES (in the time period under consideration it was located at a heliocentric distance of 3 AU, at an angular distance of 70° to the East of the Sun–Earth line and 3° to the South of the ecliptic plane) and GRANAT (which was orbiting around the Earth spending most of its flight time outside the Earth's magnetosphere). An approximation is made of the complex time profile of the enhancement of the solar cosmic ray (SCR) intensity on the basis of the reflection model of their propagation in the heliosphere. It has been established that, in this event, the transport of SCR particles in the interplanetary space was mainly carried out in the traps made up by the fronts of radially moving flare disturbances. The parameters of these fronts obtained when modeling this enhancement of SCR allow one to estimate the characteristic dimensions of the regions of effective capture of SCR. Comparison of the results of approximations obtained for the data from GRANAT and ULYSSES spacecraft demonstrated an increase in the regions of capture of SCR when the radial distance from the Sun increases.     

On the Accuracy of the Conjugation of High-Orbit Satellites with Small-Scale Regions in the Ionosphere

The degree of uncertainty that arises when mapping high-orbit satellites of the Cluster type into the ionosphere using three geomagnetic field models (T89, T98, and T01) has been estimated. Studies have shown that uncertainty is minimal in situations when a satellite in the daytime is above the equatorial plane of the magnetosphere at the distance of no more than 5 R_E from the Earth’s surface and is projected into the ionosphere of the northern hemisphere. In this case, the dimensions of the uncertainty region are about 50 km, and the arbitrariness of the choice of the model for projecting does not play a decisive role in organizing satellite support based on optical observations when studying such large-scale phenomena as, e.g., WTS, as well as heating experiments at the EISCAT heating facility for the artificial modification of the ionosphere and the generation of artificial fluctuations in the VLF band. In all other cases, the uncertainty in determining the position of the base of the field line on which the satellite is located is large, and additional information is required to correctly compare the satellite with the object in the ionosphere.     

The Structure of Ion Spectra in Outer Regions of the Ring Current: The November 13, 1995 Event

We present the results on variations of ion spectra in the energy range from 1 keV to 3 MeV. The spectra measured onboard the INTERBALL Tail Probe satellite on November 13, 1995, during the satellite's passage from the dipole field lines to the lines stretched into the magnetotail are analyzed. The data of the CORALL, DOK-2, and SKA-2 instruments are used to reconstruct the ion spectra. It is shown that, when the ion spectrum along the satellite trajectory is averaged over 2-min intervals, it is smooth up to geocentric distances of 6R _E. With decreasing distances, the form of the particle spectra in the region under consideration remained virtually unchanged (region from L = 11R _E down to L= 6R _E) and only insignificant variations of the energy of the spectral maxima are observed. Possible reasons for the observed regularities are discussed.     

Statistical study of interplanetary condition effect on geomagnetic storms: 2. Variations of parameters

We investigate the behavior of mean values of the solar wind’s and interplanetary magnetic field’s (IMF) parameters and their absolute and relative variations during the magnetic storms generated by various types of the solar wind. In this paper, which is a continuation of paper [1], we, on the basis of the OMNI data archive for the period of 1976–2000, have analyzed 798 geomagnetic storms with D _st ≤ −50 nT and their interplanetary sources: corotating interaction regions CIR, compression regions Sheath before the interplanetary CMEs; magnetic clouds MC; “Pistons” Ejecta, and an uncertain type of a source. For the analysis the double superposed epoch analysis method was used, in which the instants of the magnetic storm onset and the minimum of the D _st index were taken as reference times. It is shown that the set of interplanetary sources of magnetic storms can be sub-divided into two basic groups according to their slowly and fast varying characteristics: (1) ICME (MC and Ejecta) and (2) CIR and Sheath. The mean values, the absolute and relative variations in MC and Ejecta for all parameters appeared to be either mean or lower than the mean value (the mean values of the electric field E _y and of the B _z component of IMF are higher in absolute value), while in CIR and Sheath they are higher than the mean value. High values of the relative density variation sN/〈N〉 are observed in MC. At the same time, the high values for relative variations of the velocity, B _z component, and IMF magnitude are observed in Sheath and CIR. No noticeable distinctions in the relationships between considered parameters for moderate and strong magnetic storms were observed.     

On the belt of energetic electrons at <Emphasis Type="Italic">L</Emphasis> = 2.75 in the Earth’s magnetosphere

In 1964, during flights of the ELECTRON satellites the narrow belts of energetic electrons (E _e ≈ 6MeV) have been discovered in the Earth’s magnetosphere at L ≈ 2.75. The same structures approximately at the same magnetic shells were found in 2004 by the CORONAS-F and SERVIS-1 satellites. A comparison of the results of these experiments is presented. It is shown that the additional narrow belts of energetic electrons occur after intense magnetic storms (D _st > 100 nT), in our cases, having a double-triple structure. The lifetime of these belts is a few months and their disappearance had a gradual character. The obtained results separated in time by 40 years suggest the constancy of the sources of particles of the Earth’s radiation belts and processes occurring in the magnetosphere, which ensures not only existence of the radiation belts, but also the recurrence of various exotic phenomena in the belts similar to the belt of energetic electrons at the inner magnetic shells.     

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.     

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.     

Bursts of geomagnetic pulsations in the frequency range 0.2-5 Hz excited by large changes of the solar wind pressure

We present the results of studying the magnetospheres’s response to sharp changes of the solar wind flow (pressure) based on observations of variations of the ions flux of the solar wind onboard the Inreball-1 satellite and of geomagnetic pulsations (the data of two mid-latitude observatories and one auroral observatory are used). It is demonstrated that, when changes of flow runs into the magnetosphere, in some cases short (duration ~ < 5 min) bursts of geomagnetic pulsations are excited in the frequency range Δf~ 0.2–5 Hz. The bursts of two types are observed: noise bursts without frequency changes and wide-band ones with changing frequency during the burst. A comparison is made of various properties of these bursts generated by pressure changes at constant velocity of the solar wind and by pressure changes on the fronts of interplanetary shock waves at different directions of the vertical component of the interplanetary magnetic field.     

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.     

Large and sharp changes of solar wind dynamic pressure and disturbances of the magnetospheric magnetic field at geosynchronous orbit caused by these variations

The large and sharp changes of solar wind dynamic pressure, found from the INTERBALL-1 satellite and WIND spacecraft data, are compared with simultaneous magnetic field disturbances in the magnetosphere measured by geosynchronous GOES-8, GOES-9, and GOES-10 satellites. For this purpose, about 200 events in the solar wind, associated with sharp changes of the dynamic pressure, were selected from the INTERBALL-1 satellite data obtained during 1996–1999. The large and sharp changes of the solar wind dynamic pressure were shown to result in rapid variations of the magnetic field strength in the outer magnetosphere, the increase (drop) of the solar wind dynamic pressure always lead to an increase (drop) of the geosynchronous magnetic field magnitude. The value of the geomagnetic field variation strongly depends on the local time of the observation point, reaching a maximum value near the noon meridian. It is shown that the direction of the B _z component of the interplanetary magnetic field has virtually no effect on the geomagnetic field variation because of a sharp jump of pressure. The time shift between an event in the solar wind and its response in the magnetosphere at a geosynchronous orbit essentially depends on the inclination of the front of a solar wind disturbance to the Sun-Earth line.