Physics of auroral phenomena : proceedings of the 38th annual seminar, Apatity, 2-6 march, 2015 / [ed. board: A. G. Yahnin, N. V. Semenova]. - Апатиты : Издательство Кольского научного центра РАН, 2015. - 189 с. : ил., табл.

“P hysics o f Auroral P henom ena ”, Proc. XXXVIII A n nua l Sem inar, A patity, pp. 15-19, 2 0 1 5 © Kola Science Centre, Russian Academy of Science, 2015 Polar Geophysical Institute SUBSTORM INJECTION AT THEMIS SATELLITE AND NEAR­ CONJUGATE AURORAL LUMINOSITY IN PRE-MIDNIGHT SECTOR: THE CASE STUDY T.V. Kozelova, B.V. Kozelov (Polar Geophysical Institute, Apatity, Russia) Abstract. We use spacecraft observations from THEMIS during a substorm on 19 Dec 2014, in conjunction with ground-based magnetic field observations and the aurora at the station Apatity , to examine the spatial structuring and temporal variability of the localized auroral intensification in pre-midnight sector. In this substorm the THEMIS at r ~ 7-9 RE observed the high energetic particle injections and the sharp density decreases of less energetic particles simultaneously with the oscillations both with quasi­ period of 30-40 s and the one oscillation with quasi­ period of 2.5 min which occur near the substorm expansion phase onset. We discuss a possible association o f particle dynamics and the magnetic and electric field variations during the substorm intensification. 1. Introduction Lyons et al. [2003a] show that a reduction in equatorial plasma pressure within the current wedge simultaneous with the increase in energetic particle fluxes and dipolarization is a general feature of some substorms within the equatorial inner plasma sheet at 10-13 RE. There have been very few direct measurements of the change in equatorial plasma pressure within the near- Earth plasma sheet during substorms [Roux et al., 1991; Lui et al., 1992]. Similar reduction in plasma pressure during the local dipolarization was observed by CRRES at ~6 Re [Kozelova et al., 2003; Kozelova et al., 2006]. However, the contribution of this plasma pressure reduction in the current wedge formation (and thus in the substorm expansion phase) are not examined in detail. Here we use spacecraft observations from THEMIS at 7-9 R e during a substorm on 19 Dec 2014, in conjunction with the aurora observations at Apatity station (APT), to examine the spatial structure and temporal variability of the localized auroral intensification in pre-midnight sector. 2. Substorm evolutions The evening of 19 December 2014 was characterized by long-lasting ground magnetic activity of 100-150 nT. Substorm auroral onset is identified by a brightening consisting of beading structure along the onset arc near APT at ~ 18:23 UT. Fig. 2 shows from top to bottom: the auroral activity development (the auroral keograms) observed at APT, the magnetic field and the ion flux data observed at THD (panels a-e) and the H components at several ground-based stations during three activization 'АГ- 'A3' (panels f-h). One can see westward propagation of the magnetic activity from DIK (the activization 'АГ on the panel j) to SOR (the activization 'A3' on the panel h). Thus, THD was located westward of the activization 'Al' site and eastward the activization 'A3'. From Fig. 2 one can see that each activization 'Al'- 'A3' has such general features in the magnetosphere: the increase of the magnetic disturbances and the magnetic field dipolarization; a reduction in equatorial ion pressure simultaneously with the well-known expansion phase (EXP) increase in energetic particle fluxes (injections noted as /1-/3). 3. Initial substorm activization A l dynamics In this paper, we examine at detail the changes of the magnetic field and the ESA ion pressure within the equatorial inner plasma sheet at ~7-9 RE during the first substorm activization A l. In this time besides THD, second satellite THE was located within sector between THD and substorm onset near the AMD meridian. In this interval the weak growth phase arc was oriented approximately in the east-west direction along the 68° latitude. The auroral beads propagate azimuthally westward and evolve into wavy structures, indicating that the beads are an auroral manifestation of onset waves. The arc brightenings were observed at the moments '/,'=18:18 UT and 72'= 18:22 UT. Then at the moment 7^=18:24 UT these wavy structures expand poleward more quick, indicating on the substorm expansion phase [Voronkov et al., 2003]. E and В field oscillations in the magnetosphere. Fig. 3 presents the E- and В-field data at THD and THE. At this figure, the panels 'a'-'c' show the data at THD from top to bottom: the Bz component of the magnetic field and the Ex and Ey components of the electric field. The panels 'd'-'h' show the data at THE: the B2 component of the magnetic field; P/2-1ike fluctuations of the magnetic field calculated as the deviations of observed Figure 1. Location of the ground-based stations and the projections of the THD and THE satellites on 19 December 2014 at 18:00-20:00 UT. 15