Physics of auroral phenomena : proceedings of the 35th Annual seminar, Apatity, 28 Februaru – 02 March, 2012 / [ed. board: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2012. - 187 с. : ил., табл.

Т. V. Kozelova and В. V. Kozelov nonlinearly unstable with respect to the excitation of the Kelvin-Helmholtz (KH) mode in the equatorial magnetosphere as it was shown by Voronkov et al. [1999]. Indeed, one can see in Figure 2 that the azimuthal component of the electric field, Ey, increases with time delay ~ 10-15 s and oscillates with the same period ~50 s. The foldes on the the auroral arc observed in this time (Fig.l) are visible evidence of the KH instability. An increase of the E-field magnitude and a change of the Ey sign were observed simultaneously with explosive stretching of the magnetic field in the moment ‘1’. Similar brief cross-tail electric field reversals from dawn-dusk to the dusk-to-dawn often appear prior to the beginning of substorm on r - 6.3-6.6 Re [R oux e t al., 1991; Maynard e t al., 1996; Kozelova et al., 2004]. Boundary o f trapped ions. The clearest peculiarity of the ion behavior is appearance of the ion isotropic boundary near 18:34 UT (moment ‘1’), when both the ion density and ion pressure are sharply dropping (not shown). After this drop the ion pressure was not isotropic. The non-zero non-diagonal components of pressure indicate existence o f dissipation and violation of the frozen-in condition. The variations of ion temperature components correspond to heating of ions aligned to magnetic field (not shown). This is a boundary of trapped ions. The explosive stretching of magnetic field discussed above happens just at this boundary (at ~6.3 Re). Inner edge o f electron plasma sheet. It is know that the convection boundaries, often called ‘Alfven layers’, separate spatial regions in which qualitatively different particle drift paths are present.The electrons with energies W<WC (here Wc - the cutoff energy) convect toward the spacecraft position from the tail [Kerns et al., 1994]. The cutoff energy increases during the tailward crossing of the inner plasma sheet boundary. In -18:12 UT the THEMIS-C satellite was located at radial distance ~ 5.6 Re and crossed the inner boundary of the plasma sheet from the Earth to the tail. From this moment up to ~18:28-:30 UT there were observed two populations of particles: first one contains ‘old’ trapped electrons of 8-10 keV and second one - new ‘fresh’ electrons (1 keV to -10 keV) at the opened drift trajectories (not shown). In 18:28-:30 UT, these two populations were totally mixed and became the common population. After 18:32:50 UT during 40 s, the cutoff energy of electrons increases from 8 keV to 20 keV due to small increase of Ey field (Fig.2). The inner edge of the plasma sheet steepens during later growth phase of the substorm. The electron fluxes are varying at the boundary according to Ey field perturbations. After activation at the moment ‘3’, the flux of these electrons reached of its maximum value and an injection of energetic electrons was observed. mapped in UT. Loparskaya ASC Fig. 1 Selected auroral images from Loparskay all-sky camera on Jan 6, 2008 (left), and two of them are geographic coordinates (right). The THEMIS-C footprint marked in the maps for the interval 18:30-18:44 2 2