Physics of auroral phenomena : proceedings of the 34th Annual seminar, Apatity, 01 - 04 March, 2011 / [ed.: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 231 с. : ил.

Changes in the magnelospheric cross-tail current during substorm as observed by THEMIS In this time at ~6.5 RE the THA saw the large scale magnetic field line stretching and the increase of small- scale oscillations of the magnetic field with a period of 60-80 s. The subsequent Alfven layers o f 7-9 keV electrons were observed at the THA as during substorm growth phase. At 21:07 UT the small current j E appears at 6.5 Re simultaneously with brightening of auroral arc which move to the south at Loparskaya and SOD. The time delay between the Bx and the Bz increases suggests that the local djE region expands Earthward of the THA. At ~ 21:08:30 UT a local burst of current j E appears suddenly at ~ 6 REsimultaneously with an enhancement of average electron energy from ~2.3 to 4 keV (not shown). However this current djE sinks quickly. The local disruption region earthward of THA did not produce considerable change of В field tailward of it. Auroral breakup. The ground data show that the main auroral activity moved from the east to the west. At ~21:09 UT the bright spot was to the east of SOD, and at ~21:10 UT the sharp western edge of the WTS appeared to the west of SOD. We use this moment of breakup as the onset of the explosive stage (T np = 21:10 UT). At T n p new local djE occurrs at ~11RE (moment 'tc'). Simultaneously the injection of the electrons 10-200 keV and ions <100 keV occurs at the THA. We suppose that just in this time the field line threading the THA has the equatorial crossing point at the CD region. At 21:10-21:15 UT (from 'tc' to 'td') one can see rapid dynamical changes in the magnitude, orientation and location of the perturbation current at -10- 11 RB. The djE alternated with the djw which slow down the development of the dipolization. At ~21:15 UT from ground data a new increase of westward electrojet occurs simultaneously with sharp variation of the D-component at AND. In this time in the magnetosphere the injection of energetic particle was observed at the THC. At 21:16-21:20 UT the djE occurred at -12 RE and probably the THC field line threaded the CD region. 4.2 High-latitude intensification At -21:55 UT a new westward electrojet was observed at stations BJN-HOR-LYR, poleward of the latitude of the previous -21 UT activity. Besides, BJN and HOR saw the variation of the Z)-component which is the ground signature of a WTS. In the magnetosphere, at 21:53 UT the current djw increases suddenly at -13.5 RE, presents the magnetic field line stretching observed at Гтна = (-7, 0.1, -2.4) Re and гтас = (-11, 0.8, -3.8) RE and the local dipolarization at the third more distant spacecraft THB, гтнв = (-25.1, -12.1, -12.6)RE (not shown). At 21:54 UT (the moment 'k0') the first local perturbation current djE appears at -12.5 RE(tailward of the THC) (Fig.4). Then, the impulses of the djE follow at 11.5-12.5 RE and at 7.5-8.5 RE. The time delay between the impulses of the djE at different distances may suggest that the local djE region expands Earthward. We will consider in details the dynamics of the particles and fields during the first impulse. At 21:56:45 UT (the moment 'kC'), significant increase of the djE was observed at -11.6 RE simultaneously with oscillations of the magnetic and electric fields (with period of -12 s) and the energetic particle injection on the THC. This local dipolarization and energetic particle injection was accompanied by sharp drop of total particle pressure. The pressure was restored when the current djw appeared at - 11.6 RE. At - 21:58 UT (the moment 'kA') the particle injection, the particle pressure drop, the local dipolarization and an increase of magnetic pulsation were observed by the THA at r— 8 Re. Thus, the front of dipolarization displaces Earthward with the velocity about 340 km/s. Fig. 4. The same as Fig.2, but for high-latitude intensification. 5 Discussion Lorez et al [1989] concluded that the features of dipolarizations and the associated injections of energetic particles at distances <10 RE depend on the position of the observing spacecraft relative to the neutral sheet. A spacecraft located near the neutral sheet will observe an increase in the total magnetic field magnitude, whereas a spacecraft placed far from the neutral sheet will observe a decrease in the field magnitude. We found that at - 4-13 RE the current disruption develops discretely by creating new localized CD site outside previous activity. In this situation, the spacecrafts below the neutral sheet saw complex picture. Sometimes the dipolarization and particle injection may seem to be not associated. Fig. 5 presents a schematic illustration of position of spacecrafts THA and THC relative to the sites of j E (the circles with a cross) and djw (the circles with a point) in different moments of substorm development (1-4). We show outlines of magnetic field lines before some of these moments. 15