S. A. Zaitseva

Growth rate and decay of magnetospheric ring current

Abstract The rate of energy input to the ring current is studied as a function of solar wind parameters. The ring current dissipation rate is also examined. The decay constant τ in the main phase of a storm has been shown to be independent of its intensity and to equal (4 ± 2) h. In the recovery phase τ rises with increasing storm intensity.

The structure of the solar flare stream magnetic field

The structure of the interplanetary magnetic field within the flare streams as well as associated variations of the geomagnetic disturbancy are considered. It is shown that in the main body of the flare stream the magnetic field is determined by the configuration of the large scale magnetic field on the Sun at the flare region. Within the head part of the flare stream the magnetic field represents by itself the compressed field of the background solar wind and hence is determined by the distribution of the super large scale solar magnetic field outside the flare region.A certain asymmetry in the parameters of the magnetic field within the streams associated with geoeffective and non-effective flares is shown to exist.

Magnetosheath model in the Chew–Goldberger–Low approximation

Parameters of the solar wind plasma and magnetic field in the magnetosheath are calculated for an anisotropic plasma model in the Chew–Goldberger–Low approximation. It is shown that in the case when the energy transfer between the perpendicular and parallel (with respect to the magnetic field) degrees of freedom is absent, the resulting temperature anisotropy may significantly affect the plasma density and magnetic field intensity profiles across the magnetosheath. However, in this case, the value of the temperature anisotropy (the ratio of the perpendicular to the parallel component of the temperature with respect to the magnetic field, T⊥/T‖) becomes unrealistic high. To bring agreement between the model values of the temperature anisotropy and experimental data, the existence of an intensive proton pitch-angle diffusion is assumed. In the case when the temperature anisotropy relaxation time is much smaller than the time taken by the solar wind plasma to move from the bow shock to the magnetopause, one ...

Electric fields and currents in the earth's polar caps

Abstract A model for solar wind flow around the magnetopause incorporating a stagnation line at the frontside magnetopause is used to derive a formula for the electric field intensity and polar cap potential drop. These relationships are compared to experimental data from polar orbiting satellites. The relation between solar wind parameters and auroral arc velocity is also studied.

Dynamics of aurorae in the cusp region and characteristics of magnetic reconnection at the magnetopause

The development of dayside auroral breakups is studied, and results are compared with the magnetic field reconnection model. It is shown that periods of poleward motion of auroral arcs are preceded by relatively short (T ∼ 100 s) intervals of equatorward auroral expansion. These equatorward motions are analogous in some aspects to poleward jumps of aurorae at the night side of the oval during auroral substorms, and they are thought to be the direct signatures of magnetic field reconnection pulses at the magnetopause. FTEs associated with dayside breakups are shown to be rather large-scale phenomena, the lengths of the reconnection line at the magnetopause equals 4–6 RE, and “the meridional” extent of the reconnected tube along the magnetopause is also about 4 RE. The rate of energy input into the reconnection region is estimated.

LARGE-SCALE ELECTRIC FIELDS IN SOLAR FLARE REGIONS

A method of separating electric field in the flare region in the potential and vortex (induced) parts is discussed. According to the proposed model, the motion of flare ribbons from the central line of the flare region is caused by the vortex component of the coronal electric field, while the motion of bright spots within the flare region towards the central line is driven by the potential component of that field. The intensity of both the components of the flare region electric field is estimated to equal approximately 1–3 V cm−1, which provides the input of the electromagnetic energy into the active region at a rate of about 1010 erg cm−2 s−1.

MHD-modelling of the magnetosheath

Abstract A short discussion of some problems of magnetosheath physics is presented. In particular, anisotropic MHD models of the magnetosheath are discussed. A method to estimate the value of the characteristic relaxation time (τ) of the proton temperature anisotropy from experimental data is proposed. Another problem considered in the review concerns the conditions of formation of a magnetic barrier within the magnetosheath. The existing controversy in this question is explained in the authors’ opinion by different definitions of the term “magnetic barrier” used in papers by Pudovkin et al. J. Geophys. Res., 87 (1982) 8131; Ann. Geophys. 13 (1995) 828) and Phan et al. J. Geophys. Res. 99 (1994) 121). Experimental data on the magnetic barrier dependence on the IMF orientation are discussed.

Proton pitch angle diffusion rate and wave turbulence characteristics in the magnetosheath plasma

[1] Results of the analysis of variations of the proton temperature anisotropy (A) across the magnetosheath along with some plasma wave turbulence characteristics are discussed. It is shown that the deviation of the observed values of A from the bounded anisotropy model may be explained by a finite value of the temperature isotropization time t. In turn, the obtained values of t have a tendency to decrease with the increase of the intensity of the magnetic field oscillations. The discovered dependence of t on the intensity of mirrorwave-like turbulence seems to confirm the supposition by Hill et al. [1995] on a significant role of mirror waves in the pitch angle scattering of protons in the magnetosheath plasma. It is shown that the observed periods of abnormally low values of A in some cases correspond to the periods of relatively high intensive magnetic field oscillations, most probably of an external origin. INDEX TERMS: 2728 Magnetospheric Physics: Magnetosheath; 2752 Magnetospheric Physics: MHD waves and instabilities; 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions; 2724 Magnetospheric Physics: Magnetopause, cusp, and boundary layers; KEYWORDS: proton temperature anisotropy, magnetosheath, proton pitch angle scattering, AMPTE/ IRM, plasma wave turbulence

Dependence of the flare stream velocity on magnetic field orientation

The main parameters of a flare stream-its velocity, magnetic field intensity, plasma density, and temperature - are shown to depend on the mutual orientation of magnetic fields in the main body of the stream and within its compressed solar wind region. In particular, the plasma velocity and frozen-in magnetic-field intensity within the main body of the stream, as well as the plasma density and temperature, and the magnetic field intensity within the compressed solar wind region, are maximum when the magnetic fields in the two regions are antiparallel to each other, and minimum when the fields are parallel.The mutual orientation also affects the characteristics of the flares and, in particular, the probability of solar type IV radio emission.The results obtained are explained within the framework of a model that takes into account magnetic field reconnection at the front surface of the stream body.

The magnetopause erosion and the magnetosheath magnetic field penetration into the dayside magnetosphere

Abstract The earthward displacement of the magnetopause observed during a southward IMF (or the magnetopause erosion) and its dependence on the solar wind plasma and magnetic field parameters is studied by investigating data of about 30 magnetopause crossings by the ISEE 1 and 2 spacecraft. It is shown that the magnetopause erosion may be explained by a depression of the magnetic field intensity in the dayside magnetosphere caused by the penetration of the magnetosheath magnetic field (component perpendicular to the reconnection line) into the magnetosphere. The penetration coefficient (the ratio of the intensity of the penetrated field to the intensity of the magnetosheath magnetic field) is estimated and found to equal approximately 1.