A. Bochev’s research while affiliated with Bulgarian Academy of Sciences and other places

We show examples of long period Pc5 magnetic field pulsations near field-aligned current (FAC) regions in the high-latitude magnetosphere, observed by INTERBALL-Au, and coordinated with POLAR, GOES-9 and ground-based observations during 11 January and 11 April 1997. Identification of corresponding magnetosphere regions and subregions is provided by electrons and protons in the energy-range of 0.01–100 keV measured onboard the spacecraft. The ULF Pc5 wave occurrence is observed in both upward and downward FACs. A fairly good correlation is demonstrated between these ULF Pc5 waves and the consecutive injection of magnetosheath low energy protons. The constancy of the observed frequency peak at 1.8 mHz during quite unsteady solar wind pressure conditions could be reconciled with the surface wave mode model. The 3.1 mHz peak location area probably resembles field-line fluctuations with an interesting appearance of poloidal mode oscillation. It is suggested that the 1.3 mHz wave and its harmonic 2.6 mHz represent global compressional oscillations.

In this paper we study a possible existence of surface wave (SW) global modes of the outer magnetosphere. The SW modes are supported by two plasma discontinuities: the plasmapause and the boundary between the open and closed field lines of the magnetosphere. Conditions under which the SW global modes can propagate azimuthally and along the magnetic field lines are examined. The ionosphere at the ends of the field lines is considered as reflecting boundaries of these SW modes. As a result SW standing wave structures along the magnetic field fluxes can be formed. Two branches of SW modes are derived. The low frequency branch, fs,1 falls in the Pc5 range, while the high frequency branch, fs,2—in the Pc4 range, where fs,1(2) is the fundamental SW global mode frequency. Their frequencies possess quantized properties in the following way: f≡(1,2,3, …)fs,1(2). The high frequency SW branch, fs,2 exists only for relatively great azimuthal wavenumbers k⊥. It is pointed out that most of the SW global mode characteristics are similar to those of the FLR. These results are applied to 1.8 mHz global mode observations on 11 January 1997. Spectral, phase and polarization properties of this Pc5 pulsation event under northward IMF conditions are examined as we see them from ground-based (L’Aquila and TNB observatories) and satellite (POLAR and INTERBALL) observations.

This paper discusses observations of dynamic magnetic field variations on auroral field lines at mid and high altitudes, utilizing a conjunction of POLAR and INTERBALL-Auroral spacecraft in the dusk magnetosphere on January 11, 1997. Both spacecraft indicate the presence of periodic magnetic variations in the Pc5 frequency range in the field-aligned current region 1. The satellites are believed to be closely on the same field line or within a flux tube (radius 130 km of its projection in the ionosphere). The polarization analysis shows an interesting event: a rotation of the main polarization axis by about 90° between POLAR and INTERBALL. When the two spacecraft are very close to a common field line, the difference between their observed magnetic fields might arise from a rotation of the field between the two altitudes. We cannot exclude different polarization properties arising from different horizontal positions (although small) of both satellite with respect to local plasma boundary. Frequency analysis of both solar wind density (WIND) and INTERBALL magnetic field showed that the solar wind pressure variation contains the same spectrum (2.4–4.4 mHz). It appears that the solar wind pressure variations are sufficient for a parametric mechanism of excitation of compressional disturbances propagating along the magnetopause and within the magnetospheric cavity.

We present magnetograms suggestive for unusual field-aligned currents (FACs) appearance in mid-altitude cusp of the magnetosphere at height 20,000 km during ejecta on 11 April 1997. In fact FACs are different as compared with Potemra model nevertheless that current direction may coincide with the classical system. We demonstrate: (1) an appearance of two or more current sheets with opposite polarities in the dusk flank of the cusp; (2) appearance of FAC system in a comparatively large magnetic field depletion or diamagnetic cavity. The examination of energetic particles gives evidence to suppose a simultaneous formation of cusp energetic particle (CEP) event in the region of field-aligned currents and diamagnetic cavity; (3) an unusually intense FAC system is documented in the cusp during low geomagnetic activity (Kp=2), when the magnetic field disturbance was in the order of 150 nT. This result together with POLAR study [16] is more confident conclusion that the driving process for this event including the reversed convection (sunward) through the polar cap was the reconnection between interplanetary field lines and the lobe field lines.

We study an excitation mechanism of the field line resonances FLR by the solar wind pressure changes that induces magnetic field component disturbance b z parallel to the Earth s magnetic field at the magnetopause The latitudinal FLR magnetic field amplitude and phase distributions are to be well related to this magnetic component b z The theoretically predicted FLR characteristics with the use of measured solar wind and IMF parameters are compared with the amplitude and phase properties of Pc 5 pulsations observed on 11 January 1997 both on board the Interball and Polar satellites in the dusk magnetosphere and on the ground The comparison with the satellite observations demonstrates that the localization and polarization feature of the Pc 5 pulsation seems to be explainable by the FLR theory However comparison with ground based data reveals differences that are not compatible with this theory Other mechanisms e g cavity and surface wave modes etc are invoked in order to understand the diversity of the ground based data

In this work, the cases of magnetic field disturbances registered aboard the INTERBALL-Auroral Probe satellite /IMAP Magnetometer in the north mid-altitude cusp have been analyzed. Cusp subregions are investigated by the energetic particle experiments (PROMICS-3 and DOK-2) on the same spacecraft. Images from the DMSP satellite are used for a better definition of the auroral oval. Unusual cases of field-aligned current (FAC) concentration are demonstrated: (1) Strong and highly structured FACs concentrated in the dawn cusp flank; (2) FACs concentrated in a zone of diamagnetic cavity in the dusk flank of the cusp probably related to a cusp energetic particle (CEP) event. The examined cases demonstrate that these regions of concentrations of FACs connect to the outer magnetosphere.

In the present work we analyse the magnetic cloud (MC) at 1 AU on 9 November 1997. The appearance of a hotter and dense part (dense filament), with radial extent 106 km, immediately behind the frontal part of the MC, is a distinctive feature of the event. The INTERBALL - Aurora] Probe had a chance to observe field-aligned currents in the mid - altitude magnetosphere during the substorm expansion phase intensification related to the dense filament. We emphasise the appearance of unusual “N”- shape magnetic structure, duration 3 min, amplitude 50 nT between field-aligned current region 1 and the magnetosphere lobe in the late evening hours. To explain some of the MC features we refer to a model scenario of the 6 November 1997 coronal mass ejection.

Assuming an assembly of field-aligned current (FAC) elements, the interaction of FAC elements irrespective from their wave/static nature is examined. Considering that the FAC assembly elements are governed by the Gibbs distribution module Θ we arrive to a macroscopic/fluid description of the FAC systems. Solutions of the derived nonlinear differential equation yield periodic spatial structures of the FAC systems in the magnetosphere. The FAC structures are a consequence of the pattern formation process that appears owing to the FAC intensity increase down the magnetic field lines. It is shown that critical values (threshold values) for an initiation of FAC structure formation exist. A coexistence of large-scale and intermediate-scale FAC structures is possible above threshold values. The threshold values depend on the ambient plasma temperature and the spatial scales of the newly formed FAC structures. Generally, the critical values are easily attainable for low β plasma conditions realizable for the magnetosphere regions just above the ionosphere.

On board the Auroral satellite the magnetometer IMAP- 3 (STIL) and SKA-3 provide in-situ characteristics of the magnetic field , and of the electrons and ions, respectively. The UV Spectrometer UVSIPS maps ionospheric auroral characteristics in the magnetic field line foot print in 3 lines: 1304 A^o, 1356 A^o and 1493 A^o. On 10/27/1996 a phenomenon was found at the polar edge of the auroral oval in the postmidnight - morning sectors: field-aligned (FA) high-energy upward electron beams in the energy range 20-45 keV at altitudes about 3R_E, accompanied by bidirectional electron FA beams of keV energy. The beam intensity reaches more than 10^4 electrons/s sr keV cm^2 for a time ˜3 10^2-10^3 seconds, when the satellite at the apogee moves slowly within the ILAT-MLT frame.The location of the beams is consistent with a region of downward FA current.We suppose the satellite is in between the bidirectional acceleration regions where a stochastic FA acceleration is accomplished by waves (lower - hybrid, ion -cyclotron, ion-sound, Langmuir and/or lower-hybrid cavitons, or ion holes ) with fluctuating FA electric field components in both directions. Thise case contributes to solving the scientific aims of the Interball project essential understanding of the system Solar wind - Magnetosphere - Ionosphere.

The Interball project investigates the system solar wind-magnetosphere- ionosphere by Auroral and Tail probes. On board the Auroral satellite , SKA-3 (a set of particle detectors) and the magnetometer IMAP-3 provide in-situ characteristics of the energetic particles and the magnetic field, respectively. The UV Spectrometer UVSIPS maps the ionospheric auroral characteristics in 3 lines: of the atomic oxygen (1304Å, 1356Å) and nitrogen (1493Å). The co-ordination of the satellite and the ground-based measurements allows to clarify the solar wind-magnetosphere-ionosphere interactions and to contribute in understanding the magnetospheric models.The purpose is to present examples of the observations demonstrating the quality of the data recorded by the instruments.