A. Bochev

Intense current structures during low geomagnetic activity and their relation to small-scale magnetic perturbations seen by the Intercosmos Bulgaria-1300

Abstract This paper deals with the initial observational data on the field-aligned currents (FAC) and the small-scale transverse magnetic perturbations (SSTMD) in the cusp region obtained from the magnetometer on board the Intercosmos Bulgaria-1300 satellite. The magnetic field has been investigated by a high accuracy flux-gate magnetometer, IMAP, designed in the Central Laboratory for Space Research (CLSR), Sofia. For low geomagnetic activity 10 meridional passes (September–December 1981) have been examined. Intense FAC are observed in the noon sector of the summer auroral region. SSTMD are superimposed on a weak cusp current as a perturbation in the prenoon sector of the winter auroral region.

Quasi-periodical small-scale magnetic disturbances in the low-altitude cusp

Abstract Satellite data from measurements of thermal plasma and electric and magnetic fields are considered for the low-altitude cusp. Small-scale magnetic disturbances (SSMDs) are studied in relation to other plasma parameters. The SSMDs sometimes have a quasi-periodical structure and probably a compressional component. The analysis of their polarization structure provides grounds to conclude in some cases at least that the SSMDs represent compressional surface MHD waves.

Field-aligned current signature in the dusk magnetosphere by INTERBALL-AU and POLAR

Abstract The POLAR and INTERBALL-AU spacecrafts magnetic field experiments allow investigation of the time-spatial variation of field-aligned current structures at mid and high altitudes. The study includes two intervals over north high latitudes in the dusk magnetosphere: (1) 10 January 09 – 11 UT (consecutive transits) and (2) 11 January, 03 – UT (nearly conjugate situation at ∼04:30 UT). By using both spacecraft, the identification of current regions is more confident. On January 11 cycles of the polarization reversal of small-scale disturbances in the poleward portion of region R1 have been detected at high and mid altitudes.

Field-aligned currents and related phenomena in the cusp

Abstract This review deals with observations of field-aligned currents (FAC) based on measurements of magnetic and electrical fields, particle fluxes (0.2–15 keV) and plasma parameters, provided by the INTERCOSMOS BULGARIA-1300 satellite. Special attention is paid to the cusp sector (10–14 MLT). The current regions inferred from the satellite magnetometer are compared with the charecteristics of the dayside oval and the cusp derived from a variety of parameters. Our topics are as follows: penetration of region 1 in the cusp; FAC reversals and plasma convection; thermal plasma structure and collocation of FAC; Associations with the IMF components etc.

Small-scale magnetic disturbances in the cusp and polar cap regions

Abstract In this paper we present further investigation of the small-scale transverse magnetic disturbances (SSTMD) based upon magnetic field, electric field and particle fluxes data acquired by three satellite experiments. Only the magnetic disturbances occurring poleward of the field-aligned current regions 1 and 2 will be considered in the examination and classification. On the basis of the data acquired the reliability of the small-scale transverse magnetic disturbances in the cusp region and processes of penetration of magnetosheath plasma in the cusp region are pointed out.

Energy deposition in the polar ionosphere as determined by measurements aboard ‘INTERCOSMOS-BULGARIA-1300’ satellite

Abstract Data were obtained from the measurements of optical emissions, ion drift, DC magnetic field and energetic particles, on board INTERCOSMOS - BULGARIA - 1300 satellite. In two cases of night-time passes through auroral oval, an estimate has been made of the energy input by particle precipitation and Joule heating. In order to determine the Joule heating, the Pedersen currents flowing in the lower ionosphere were determined. In orbits 231 and 203 Pedersen currents of 0.94 Am −1 and 0.71 am −1 were observed. From these values estimates of Joule heating rates of2 × 10 −7 Wm −3 and8 × 10 −7 Wm −3 were obtained. The integral energy deposited by the precipitated particles was also estimated in the current systems regions. The possibility for identification of the auroral electrojet based only on satellite data is pointed out.

Magnetic field measurements in the ionosphere-magnetosphere region

Abstract An analysis of the differences between the measured by the Intercosmos Bulgaria 1300 satellite and the computed from the IGRF-1980 values of the magnetic field intensity is presented. In a global scale the residuals are negative. A 75 nT spacecraft remanent magnetic field along the X-axis is determined. Partially the negative residuals could be explained by the model itself which results in a stronger field than the actual one. The spacecraft inductive magnetization may be a reasonable explanation for the rest. It is difficult to explain the negative residuals in the polar region by a magnetization along any of the axes. The complex character of the differences in this region is conditioned by the external fields, in particular, by the ionospheric current systems. The authors believe that the bias fields from the spacecraft have a static character and they are restricted mainly along the X-axis.

Thermospheric heating at high latitudes as observed from Intercosmos-Bulgaria-1300 and Dynamics Explorer-B

This paper reports the results of the first direct comparison of near simultaneous measurements obtained by the INTERCOSMOS-BULGARIA-l300 and the DYNAMICS EXPLORER-B satellites. The ICB—l300 is in a near circular orbit at a mean height of about 850 km. The DE-B satellite in an elliptical orbit is sometimes directly below the ICB-1300 satellite providing an opportunity to investigate the response of the thermosphere to particle fluxes from the magnetosphere. Energy fluxes in the range 0.2 — 15 key are obtained from an energetic particle analyzer on board the ICB-1300 satellite. The thermospheric composition and density are obtained by a neutral gas mass spectrometer (NACS) on the DE-B satellite. During the period 20 August — 20 November, 1981, observations show that the times and locations of maxima in magnetospheric energy deposition coincide with regions of maximum thermospheric upwelling characterized by composition changes.

Flux-gate magnetometer measurements in the polar region at altitude 900 km

Abstract This paper deals with the total magnetic field as measured by a three component flux-gate magnetometer IMAP-1 on board the INTERCOSMOS BULGARIA- 1300 satellite. Several hundreds orbits obtained during the long active life of the satellite (Aug. 1981 till May 1983) have been examined. A precise statistical analysis of the data enables us to estimate the stray fields from the satellite. Special attention is paid to the data from high latitudes during low geomagnetic activity. The residuals △F are negative in both polar regions. Experimental data indicate intense △F perturbations (up to −100 nT) appearing together with a typical distribution of field-aligned currents. Further examination of external field is desirable in order to analyse the secular change of F at high latitudes.