Orientation of Middle-Scale Structures in the Solar Wind Plasma

An estimation of the value and orientation of the inclination of middle-scale structures in the solar wind plasma is obtained on the basis of time lags of simultaneous correlated measurements on three spacecraft: INTERBALL-1, IMP-8, and WIND. It is shown that middle-scale plasma structures, in the majority of cases, are not perpendicular to the Sun–Earth line, but inclined to it (presumably, in the ecliptic plane), on average, at an angle of approximately 63° (or 27° to the Y _SE axis). However, this inclination is significantly less than the inclination of the Parker spiral for the interplanetary magnetic field (45° at the Earth's orbit).     

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.     

Sharp Boundaries of Solar Wind Plasma Structures and an Analysis of Their Pressure Balance

This work is devoted to studying the sharp boundaries of small-scale structures of the solar wind according to the data of measurements with high time resolution onboard the INTERBALL-1 satellite and simultaneous measurements of the WIND spacecraft. Such issues as the character of change of various plasma and magnetic field parameters on these boundaries, the duration of boundary passage and the balance of the total (thermal plus magnetic) pressure on the boundaries of the structures are considered. On the basis of the vast statistical material available, the typical conditions in the solar wind are investigated, in which such sharp boundaries are observed.__________Translated from Kosmicheskie Issledovaniya, Vol. 43, No. 3, 2005, pp. 163–170.Original Russian Text Copyright © 2005 by Riazantseva, Khabarova, Zastenker, Richardson.     

Relationship between the fluxes of relativistic electrons at geosynchronous orbit and the level of ULF activity on the Earth’s surface and in the solar wind during the 23rd solar activity cycle

We present the results of a cross-correlation analysis made on the basis of Spearman’s rank correlation method. The quantities to correlate are daily values of the fluence of energetic electrons at a geosynchronous orbit, intensities of ground and interplanetary ultra-low-frequency (ULF) oscillations in the Pc5 range, and parameters of the solar wind. The period under analysis is the 23rd cycle of solar activity, 1996–2006. Daily (from 6 h to 18 h of LT) magnetic data at two diametrically opposite observatories of the Intermagnet network are taken as ground-based measurements. The fluxes of electrons with energies higher than 2 MeV were measured by the geosynchronous GOES satellites. The data of magnetometers and plasma instruments installed on ACE and WIND spacecraft were used for analysis of the solar wind parameters and of the oscillations of the interplanetary magnetic field (IMF). Some results elucidating the role played by interplanetary ULF waves in the processes of generation of magneospheric oscillations and acceleration of energetic electrons are obtained. Among them are (i) high and stable correlation of ground ULF oscillations with waves in the solar wind; (ii) closer link of mean daily amplitudes of both interplanetary and ground oscillations with ‘tomorrow’ values of the solar wind velocity than with current values; and (iii) correlation of the intensity of ULF waves in the solar wind, normalized to the IMF magnitude, with fluxes of relativistic electrons in the 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.     

Turbulent fluctuations of plasma and magnetic field parameters in the magnetosheath and the low-latitude boundary layer formation: Multisatellite observations on March 2, 1996

The results of simultaneous analysis of plasma and magnetic field characteristics measured on the INTERBALL/Tail Probe, WIND and Geotail satellites on March 2, 1996, are presented. During these observations the INTERBALL/Tail Probe crossed the low-latitude boundary layer, and the WIND and Geotail satellites measured the solar wind’s and magnetosheath’s parameters, respectively. The plasma and magnetic field characteristics in these regions have been compared. The data of the Corall, Electron, and MIF instruments on the INTERBALL/Tail Probe satellite are analyzed. Fluctuations of the magnetic field components and plasma velocity in the solar wind and magnetosheath, measured onboard the WIND and Geotail satellites, are compared. The causes resulting in appearance of plasma jet flows in the low-latitude boundary layer are analyzed. The amplitude of magnetic field fluctuations in the magnetosheath for a studied magnetosphere boundary crossing is shown to exceed the magnetic field value below the magnetopause near the cusp. The possibility of local violation of pressure balance on the magnetopause is discussed, as well as penetration of magnetosheath plasma into the magnetosphere, as a result of magnetic field and plasma flux fluctuations in the magnetosheath.     

Structure of the earth’s magnetosheath at small fluctuations in the interplanetary magnetic field direction

Spatial structure of the magnetosheath of the Earth was studied under the conditions when no sharp (more than 40° during 5 min) changes in the interplanetary magnetic field direction were observed. On the basis of 24 flights of the Interball-1 satellite through the magnetosheath, it is found that three regions differing from each other by parameters of the field and plasma can be observed in the magnetosheath under the above-indicated conditions. These regions also differ from the solar wind region before front of the Earth’s magnetospheric bow shock. Empirical distributions of parameters were studied in each region. Taking into account the influence of the interplanetary magnetic field direction on the processes in the magnetosheath, the cases of quasi-perpendicular and quasi-parallel shock waves were considered separately. The study showed that the distribution of parameters in the selected regions (in the solar wind before front of the bow shock, in the magnetosheath behind the bow shock (post-shock), in the region of the magnetosheath with minimal fluctuations in the field, and in the inner magnetosheath) differ from each other at any interplanetary magnetic field direction.     

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.     

Properties of Sharp and Large Changes in the Solar Wind Ion Flux (Density)

The results of a detailed study of large (by 20% and more) and sharp (faster than ten minutes) changes of the ion flux in the solar wind are presented. The data are provided by regular measurements onboard the INTERBALL-1 satellite in the period 1996–1999. Using statistical analysis, we obtained the distribution of these changes in their absolute and relative strength. It is shown that, for a considerable proportion of the events, such sharp and large changes of the ion flux (density) take place under conditions of fairly constant values of the solar wind velocity and of both the magnitude and components of the interplanetary magnetic field.     

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.     

Coronal mass ejections in July 2005 and an unusual heliospheric event

Using the events in July 2005 as an example, the causes and peculiarities of Forbush effects produced by solar sources remote from the central zone are discussed. The event in question differs from other effects observed at the periphery of interplanetary disturbances by strong variations in cosmic rays on the background of weak disturbances in the solar wind and magnetic field of the Earth. The cloud of magnetized plasma ejected from the Sun was large and fast, but it passed to the west from the Sun-Earth line. According to performed estimates, the mass of the ejected substance was close to the upper boundary of mass for coronal mass ejections (CMEs). Anomalous parameters and high modulation capability of the formed solar wind disturbance are explained, in particular, by the fact that it combined several CMEs and that the last fast disturbance was prepared by a series of impulsive events in the active region of the Sun. Usually, such a great mass is ejected directly after the main energy release in strong solar flares. In the given case, a powerful MHD disturbance occurred approximately half an hour after a maximum of hard X-ray burst under the conditions when gas pressure in the flare loops became close to magnetic pressure, which was just a premise of the largescale ejection.     

Effect of large and sharp changes of solar wind dynamic pressure on the earths’s magnetosphere: analysis of several events

The magnetosphere and ionosphere response to arrival of large changes of the solar wind dynamic pressure with sharp fronts to the Earth is considered. It is shown that, under an effect of an impulse of solar wind pressure, the magnetic field at a geosynchronous orbit changes: it grows with increasing solar wind pressure and decreases, when the solar wind pressure drops. Energetic particle fluxes also change: on the dayside of the magnetosphere the fluxes grow with arrival of an impulse of solar wind dynamic pressure, and on the nightside the response of energetic particle fluxes depends on the interplanetary magnetic field (IMF) direction. Under the condition of negative Bz-component of the IMF on the nightside of the magnetosphere, injections of energetic electron fluxes can be observed. It is shown, that large and fast increase of solar wind pressure, accompanied by a weakly negative Bz-component of the IMF, can result in particless’ precipitation on the dayside of the auroral oval, and in the development of a pseudobreakup or substorm on the nightside of the oval. The auroral oval dynamics shows that after passage of an impulse of solar wind dynamic pressure the auroral activity weakens. In other words, the impulse of solar wind pressure in the presence of weakly negative IMF can not only cause the pseudobreakup/substorm development, but control this development as well.     

Catalog of large-scale solar wind phenomena during 1976–2000

The main goal of this paper is to compile a catalog of large-scale phenomena in the solar wind over the observation period of 1976–2000 using the measurement data presented in the OMNI database. This work included several stages. At first the original OMNI database was supplemented by certain key parameters of the solar wind that determine the type of the solar wind stream. The following parameters belong to this group: the plasma ratio β, thermal (NkT) and kinetic (mNV ²) pressures of the solar wind, the ratio T/T _exp of measured and expected temperatures, gradients of the plasma velocity and density, and the magnetic field gradient. The results of visualization of basic plasma parameters that determine the character of the solar wind stream are presented on the website of the Space Research Institute, Moscow. Preliminary identification of basic types of the solar wind stream (FAST and SLOW streams, Heliospheric Current Sheet (HCS), Corotating Interaction Region (CIR), EJECTA (or Interplanetary Coronal Mass Ejections), Magnetic Cloud (MC), SHEATH (compression region before EJECTA/MC), rarified region RARE, and interplanetary shock wave IS) had been made with the help of a preliminary identification program using the preset threshold criteria for plasma and interplanetary magnetic field parameters. Final identification was done by comparison with the results of visual analysis of the solar wind data. In conclusion, histograms of distributions and statistical characteristics are presented for some parameters of various large-scale types of the solar wind.     

Statistical Relationships between Solar, Interplanetary, and Geomagnetospheric Disturbances, 1976–2000

Within the framework of the Space Weather program, 25-year data sets for solar X-ray observations, measurements of plasma and magnetic field parameters in the solar wind, and D _st index variations are analyzed to reveal the factors that have had the greatest influence on the development of magnetospheric storms. The correlation between solar flares and magnetic storms practically does not exceed a level of correlation for random processes. In particular, no relation was found between the importance of solar flares and the minimum of the D _st index for storms that could be connected with considered flares by their time delay. The coronal mass ejections (CME; data on these phenomena cover a small part of the interval) result in storms with D _st < –60 nT only in half of the cases. The most geoeffective interplanetary phenomena are the magnetic clouds (MC), which many believe to be interplanetary manifestations of CMEs, and compressions in the region of interaction of slow and fast streams in the solar wind (the so-called Corotating Interaction Region, CIR). They correspond to about two-thirds of all observed magnetic storms. For storms with –100 < D _st < –60 nT, the frequencies of storms from MC and CIR being approximately equal. For strong storms with D _st < – 100 nT, the fraction of storms from MC is considerably higher. The problems of reliable prediction of geomagnetic disturbances from observations of the Sun and conditions in interplanetary space are discussed.     

Peculiarities of long-wave radio bursts from solar flares preceding strong geomagnetic storms

Radio bursts in the frequency range of 100–1500 kHz, recorded in 1997–2000 on the INTERBALL-1 satellite during the solar flares preceding the strong geomagnetic storms with D _st < ?100 nT, are analyzed in this paper. The observed long-wave III-type radio bursts of solar origin at frequencies of 1460 and 780 kHz were characterized by large values of the flux S _f = 10^?15 ?10^?17 W/m² Hz and duration longer than 10 min. The rapid frequency drift of a modulated radio burst continued up to a frequency of 250 kHz, which testified that the exciting agent (a beam of energetic electrons) propagated from the Sun to the Earth. All such flares were characterized by the appearance of halo coronal mass ejections, observed by the LASCO/SOHO, and by the presence of a southward B_z-component of the IMF, measured on the ACE and WIND spacecraft. In addition, shortly after radio bursts, the INTERBALL-1 satellite has recorded the fluxes of energetic electrons with E > 40 keV.     

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.     

Theory of type III radio bursts in the interplanetary space: I. Derivation of permittivity tensor for the system consisting of electron beam and solar wind plasma

The tensor of permittivity for the system “electron beam - plasma of the interplanetary space” is derived in the approximation of geometrical optics. The problem is one-dimensional; all parameters such as density of the beam and of the solar wind plasma, and the induction of the interplanetary magnetic field are assumed to be dependent only on the distance to the Sun. The beam is generated by an active region during a solar flare, and it is a source of radio bursts of type III in the interplanetary space. The tensor of permittivity was obtained to close field equations by a material equation. On the basis of these equations it becomes possible to study theoretically the amplitude-frequency characteristics of the radio bursts as disturbances of the above-described beam-plasma system.     

Why does the total pressure on the subsolar magnetopause differ from the solar wind dynamic pressure?

Based on analysis of MHD equations and the results of numerical simulation in the magneto-sheath it is demonstrated that the total pressure on the magnetopause differs from the solar wind dynamic pressure in the majority of cases. From the equation of motion it follows that the total pressure is reduced due to deflection from the Sun-Earth line. At the same time, it increases because of formation of a magnetic barrier. This result is consistent with experimentally observed expansion of the magnetosphere for the radial direction of the interplanetary magnetic field, when no magnetic barrier is formed. In this paper we compare the behavior of pressure along the Sun-Earth line for the northward and radial interplanetary field, using the results of numerical MHD simulation and observational data from THEMIS. In the isotropic MHD approximation, the difference between the total pressure on the subsolar magnetopause at northern and radial IMFs does not exceed 10–12 percent. However, in the anisotropic approximation this difference increases up to 15–20 percent. The results of anisotropic modeling well agree with observed averaged profiles of pressure components in the subsolar magnetosheath.     

Statistical Relationships between Solar,Interplanetary, and Geomagnetic Disturbances, 1976–2000: 3

In this paper we continue the analysis of the influence of solar and interplanetary events on magnetic storms of the Earth that was started in [9, 10]. Different experimental results on solar-terrestrial physics are analyzed in the study and the effects are determined that arise due to differences in the methods used to analyze the data. The classifications of magnetic storms by the K _p and D _st indices, the solar flare classifications by optical and X-ray observations, and the classifications of different geoeffective interplanetary events are compared and discussed. It is demonstrated that quantitative estimations of the relationships between two types of events often depend on the direction in which the events are compared. In particular, it was demonstrated that the geoeffectiveness of halo CMEs (that is, the percentage of Earth-directed coronal mass ejections that result in geomagnetic storms) is 40–50%. Higher values given in some papers were obtained by another method, in which they were defined as the probability of finding candidates for a source of geomagnetic storms among CMEs, and, strictly speaking, these values are not true estimates of the geoeffectiveness. The latter results are also in contrast with the results of the two-stage tracing of the events: first a storm—an interplanetary disturbance, and then an interplanetary disturbance—a CME.     

Ascending flows in the solar atmosphere and formation of the solar wind

Some morphological features of solar magnetic fields in the chromosphere and corona are considered based on studying various observational data. These data are compared to the results of observation of the solar wind and interplanetary magnetic field, as well as to the data on fluxes of solar cosmic rays. New specific features are found in the solar wind structure, and new additional indications of sources of the solar wind are obtained. The properties of the active regions and coronal holes are considered. A model of the ascending stream-like plasma flow is suggested. It flows around the discrete arched magnetic field tubes in the solar atmosphere and stretches them out into interplanetary space.