Physics of auroral phenomena : proceedings of the 37th Annual seminar, Apatity, 25 - 28 February, 2014 / [ed. board: A. G. Yahnin, N. V. Semenova]. - Апатиты : Изд-во Кольского научного центра РАН, 2014. - 125 с. : ил., табл.

SUBSTORM INTENSIFICATION FROM THEMIS SATELLITE OBSERVATIONS AND IMF Bz COMPONENT CHANGES T.V. Kozelova, B.V. Kozelov ( Polar Geophysical Institute, Apatity, M urmansk region, 184209 R u s sia ) “Physics o f Auroral Phenomena", Proc. XXXVII Annual Seminar, Apatity, pp. 22-25, 2014 © Kola Science Centre, Russian Academy of Science, 2014 Polar Geophysical Institute Abstract. The substorm-associated changes of the particles and fields at the Earthward part of the plasma sheet are examined using data from four THEMIS satellites during the substorm intensification on January 6, 2008, when the satellites were located in the different MLT sectors of the magnetosphere. The enhanced convection field during the Bz southward turning of the interplanetary magnetic field leads to the earthward approach of the inner edge of the plasma sheet. The AlfVen convective sheets of the 0.8-10 keV electrons are observed in the evening sector. The satellite in the morning sector saw the nose-like structure of the ions 8- 10 keV. The outer boundaries of energetic particles became steeper during the substorm growth phase. Before the substorm onset, the isotropic boundary of 29 keV ions was located at radial distance 6.3 Re in the evening sector and in the morning sector at distance 8 Re. After northward turning of IMF, the quick magnetic field line stretching and Energy-Dispersed Ion Structures (EDIS) were observed at the morning sector. Then, ten minutes after the EDIS onset, the pseudo-breakup and injection of higher-energy ions (81-157 keV) occur at the evening sector. We discuss a possible association of the substorm magnetotail dynamics with IMF Bz changes. 1. Introduction Kozelova and Kozelov [2013] reported a detailed analysis of explosive local magnetic field line stretching just before dipolarization observed by THEMIS-C satellite in the pre-midnight sector during the breakup at 18:34 UT followed by local substorm of January 6, 2008. Basing on the simple line-current model, Kozelova and Kozelov [2013] proposed that observed magnetic field and particle variations could be manifestations of the magnetospheric generator of the 3-D meridional current system with the driving electric field in the meridional direction during nonlinear growth of ballooning instability when non- MHD processes are also turning on. Table 1. THEMIS spacecraft location in 18:30 UT. THE THD THC x (GSM), Re -3.2 -1.5 -6.6 у (GSM), Re -7.0 -5.8 2.18 z (GSM), Re -2.7 -1.6 -1.5 r, Re 8.2 6.2 6.8 MLT, hr 4.0 4.9 22.75 L- value 8.6 6.5 6.8 Here we continue the consideration of this substorm event on January 6, 2008 and focus now on the changes occur both in the evening and postmidnight sector. Also we will discuss a potential role of IMF Bz component changes in the substorm dynamics. Data from THEMIS satellites during the substorm event have been used. Table 1 presents the satellite location near the moment 18:30 UT. 2. Substorm evolution Fig. 1 shows Bx, By and Bz components of the IMF and the solar wind speed observed by ACE satellite in the interval 17:13 -18:13 UT which corresponds to the interval 17:50-18:50 UT which we will discuss in the magnetosphere. The horizontal line at the panel 3 (from top) presents the time interval 18:20-18:34 UT analyzed in details by THEMIS data. Sudden increase dBz> 0 from -3.5 nT to +3.5 nT (the external trigger) occurs at the moment 3 after which several long-period (with quasi­ period of 4 min) oscillations of the Bz were observed. After the moment 4, the Bz turned to Bz=- 1 nT implying a continuation of the loading process in the magnetotail. ACE January 6, 2008 Figure 1. IMF and solar wind conditions. Labeled moments 1-5 are discussed in text. 22