The close position of main satellite and subsatellite (distance between them about 1000 km) and using the similar sets of Faraday cups (VDP and VDP-S) with high resolution measurements (up to 16 Hz for the main satellite and up to 10 Hz for the subsatellite) allow us to determine the small-scale variations of the magnetopause shape and position and to estimate the velocity of the magnetopause motion.

The preliminary analysis of the data suggests that the nature of magnetopause motion depends significantly on the geomagnetic latitude:

• it seems that wavy motion of the magnetopause boundaries is preferred at the low latitude boundary layer near the equatorial plane
• radial expansion/contraction seems to be most common at the high latitude plasma mantle

Schematic drawings of the magnetopause motion for the multiple crossings at August 29 and September 2, 1995 is shown at Fig.1, 2. At these plots the dashed lines show the position of the spacecraft along the -Yse axis (other two components are negligible) and the thick bars on these lines indicate the intervals of observation of the magnetosheath plasma. The border of shadow region (upper border for Fig. 2) shows the expected shape of magnetopause according the positions of crossings observed by two spacecraft.

In this cases the surface waves should move tailward with the magnetosheath velocity (about 200 km/s). For the Fig. 1 data the typical wavelength along the Xse axis is about 7000 km and the amplitude of the waves is probably a few times higher than the distance between the spacecraft because most of the crossingsare seen by both of them.

The lower boundary at the Fig. 2 shows the position of the outer edge of the low-latitude boundary layer (LLBL) which is characterized by the sharp rise of the electron temperature.

Referencies

• Safrankova J., G. Zastenker, Z. Nemecek, A. Fedorov, M. Simersky, L. Prech. Small scale observation of the magnetopause motion: preliminary results of the INTERBALL project. Annales Geophysicae, 1997 (in press).
• Safrankova J., Z. Nemecek, L. Prech, G. Zastenker, A. Fedorov, S. Romanov, D. Sibeck, J. Simunek. Two point observation of the magnetopause motion: the INTERBALL project. Advance of Space Research, 1997 (in press).

Contact persons:

• J.Safrankova, Faculty of Mathematics and Physics, Charles University, Prague, Czech
• G.Zastenker, Space Research Institute, Moscow, Russia