V. A. Stepanov’s research while affiliated with Russian Academy of Sciences and other places

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.

Ion data acquired by the Interball-Auroral satellite during crossings of the poleward boundary of the auroral oval in the 2200-0300 MLT sector at altitudes of ~2.5-3 Earth's radii reveal the frequent occurrence of thermal and superthermal H+ ion outflows. These events are strongly correlated with suprathermal electron fluxes and broadband electromagnetic ULF waves. The pitch angle distributions give evidence of transverse heating occurring in a latitudinally narrow layer at the boundary between the polar cap and the plasma sheet boundary layer, over a broad altitude range extending up to the satellite altitude. The distributions evolve with latitude, exhibiting fluxes maximizing at pitch angles close to 90° at the poleward edge of the outflow structure and at pitch angles closer to the upward field-aligned direction at lower latitudes. The data analysis suggests that ion cyclotron resonance interaction with ULF electromagnetic turbulence can account for the observed heating, even if we cannot totally exclude that transverse velocity shears and nonresonant stochastic transverse acceleration sometimes contribute to the ion energization in view of the dc electric field fluctuations commonly observed at the same times. During the expansion phase of substorms the region of transverse heating at the poleward boundary of the discrete auroral oval exhibits a latitudinal structure characterized by an alternate occurrence of latitudinally narrow regions of intense and weak ion fluxes. These latitudinal variations are associated with magnetic fluctuations at a frequency of ~2×10-2Hz, interpreted in terms of hydromagnetic Alfvén waves. Equatorward of the heating region, the energy spectrograms recorded during the same events exhibit an energy-latitude dispersion signature with energy decreasing as latitude decreases. This dispersion is the result of the velocity filter effect due to the large-scale convection and of the poleward motion of the ion heating source associated with the poleward motion of the high-latitude edge of the active auroral region. The poleward edge of the low-energy ion structure marked by a sharp latitudinal gradient of the ion flux appears as a reliable midaltitude criterion for identifying the poleward boundary of the soft electron layer lying at the high-latitude edge of the plasma sheet boundary layer.

A method of satellite measurements of the auroral characteristics in the vacuum UV spectral region and of the characteristics of the polar ionosphere is considered. The design and the main characteristics of the ultraviolet spectrometer UVSIPS placed onboard the Auroral Probe satellite (the INTERBALL project) are described. As an example, the measured intensity profiles of the auroral λ1304 Å and λ1356 Å [OI] emissions obtained during a substorm are examined. We also present the data of parallel measurements of the auroral electron and ion distributions obtained with the SKA-3 unit of instruments.

A new 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 20–40 keV at altitudes about 3RE, accompanied by bidirectional electron FA beams of keV energy. The beam intensity often reaches more than 0.5·103 electrons/s·sr·keV·cm2, and the beams are observed for a relatively long time (~3·102–103s), when the satellite at the apogee moves slowly in the ILAT-MLT frame. A qualitative scenario of the acceleration mechanism is proposed, according to which the satellite is within a region of bidirectional acceleration where a stochastic FA acceleration is accomplished by waves with fluctuating FA electric field components in both directions.Key words. Ionosphere (particle acceleration; wave-particle interactions) · Magnetospheric physics (magnetosphere-ionosphere interactions)

First results of the SKA-3 experiment on the Auroral Probe satellite are presented. Electrons and ions in the range of energies from 30 eV up to 500 keV were measured at the heights of 10 000-20 000 km. The measurements on the nightside of the magnetosphere were used for scientific analysis in the high latitude region under conditions of a quiet and a disturbed magnetic field of the Earth. 1. During the recovery phase of a magnetic storm on December 11, 1996, an abrupt increase in intensity of energetic charged particles was observed by the Auroral Probe satellite above the polar cap. Several minutes before this event, the B z component of the interplanetary magnetic field, after a period when its value was close to zero, jumped to a stable positive value of about 2 nT. It is supposed that, as a result of the respective drastic change in the electric field in the magnetotail, the plasma sheet expanded to higher latitudes, filling the evening side of the northern tail lobe and the polar cap. The Auroral Probe and Tail Probe were above the polar cap at that time, and a burst of particles in a wide range of energies was noted there too (see Lutsenko et al., this issue). In these flux tubes (invariant latitude of about 80°, MLT ∼21-22 h), upward fluxes of suprathermal ions with energies of 30 eV and higher were found. This population is probably due to local acceleration of thermal ions by waves generated by a beam of energetic particles. 2. Upward directed fluxes of electrons (particle energy in the range of 20-45 keV) were observed at the polar edge of the auroral oval in the postmidnight and morning sectors. Quasilinear wave-particle interaction is supposed to be the reason for acceleration of these particles, which occurs in regions of plasma turbulence arising in Region 1 of the downward field-aligned current, both above and below the satellite orbit altitudes.