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.

Substorms associated with thefronts o fstreams in the solar wind The blue line on (a) delimits the intervals of CIR and RS, the black solid line shows the onset time of the substorm. Keograms on bottom panel of (b) demonstrate the clear poleward expansion of the bulge. Geotail (c) started registering fast tailward plasma flows about 14:40 UT, a flow reversal took place at ~ 14:41 UT and maximum of earthward flow is at 14:49 UT. The flow reversal is associated with a decrease of the total pressure. 2) Auroral disturbances during SHEATH event -10 October 1997 A magnetic cloud arrived at ~ 23:08 UT on 10 October and passed away at ~ 01 UT on 12 October 1997 (as deduced from Wind data). The Sheath was registered from about 16 UT to 23:08 UT. Substorm was observed at 21:39 UT. phi и «а-f 21:13 11:*i V . . . 4 1 ГГ1 1 1 1 | -Vwty I — — ' ■''-4k 4 »"I" r-T-t-J""»11"»» I I (a) Solar wind and IMF From top to bottom: total magnetic field B, three magnetic field components, SW flow velocity and Vx, density, thermal pressure, magnetic pressure, dynamic pressure Fig. (b) Auroral disturbances development by POLAR UVI Top: auroral bulge development from onset to maximal phase. The blue curves delimit the bulge region Bottom: keograms in the LBHL emission (black line) and LBHS emission (blue line) at the meridian of Geotail footprint. Vertical lines indicate the times of of plasma flows in magnetotail by Geotail data (c) GEOTAIL data From top to bottom: temperature; density, MF component Bx, total pressure, plasma |3, GSM X component of the plasma velocity 4 Auroral disturbances during SHEATH event - 10 October 1997 The format of the Figure 4 is the same as that of Figure 3, the red crosshatched region in (a) shows the time of the Sheath. Geotail (c) registers fast tailward flow with a maximum at 21:52 UT, a flow reversal - at 21:59 and earthward flows with a maximum at 22:03. The flow reversal is associated with a decrease of the total pressure. Discussion In both cases presented here, Geotail in the magnetotail registered a reversal of a tailward plasma flow to an earthward plasma flow. The observation of oppositely directed flows is interpreted as tailward movement of the reconnection site (Hones, 1979; Runov et al., 2003), the tailward flow being inside a plasmoid. In the near-Earth initiation scenario oppositely directed flows are also observed, but not organized by the magnetic field; their generation evoked by current disruption (CD), the region of current disruption and dipolarization proceeds progressively down the magnetotail (e.g. Lui et al., 2008). The earthward flow is observed in the depolarized region, the tailward flow - tailward of the CD region. So the observation of fast flow reversal by a spacecraft in the plasma sheet is a substorm signature - it indicates passage of the reconnection site around the spacecraft in the NENL model (e.g. Yahnin et al., 2006a) or passage of the current disruption region in the CD model. In the magnetotail at Geotail location a sharp decrease of the total pressure following the interval of pressure increase was observed. The total pressure decrease is associated with the time of plasma flow direction change. From the pressure balance condition, which is suggested to held across the plasma sheet and tail lobe boundary, the total pressure in the plasma sheet must be equal to the lobe magnetic pressure. The decrease below the lobe magnetic pressure characterizes that part of the magnetic energy stored in the tail, which dissipates during the 19