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.

“P hysics o fAuroral P h e n om en a P ro c. XXXIV Annual Seminar, A patity, pp . 9 -1 2 , 2011 © Kola Science Centre, Russian Academy of Science, 2011 Polar Geophysical Institute COUNTER-STREAMING AURORAL ACTIVATIONS OBSERVED DURING SUBSTORM T.A. Kornilova, I.A. Kornilov (Polar Geophysical Institute, KSC RAS, Apatity, Russia ). A b stract. On the base of THEMIS all-sky imaging array and all-sky auroral TV data from observations Lovozero, Loparskaya and Tumanny with using special effective keogram filtering, interaction of northern moving southward auroral structures with bright breakup auroral forms were found. There exist very weak, but clearly observed traces of the northern structure penetration through the active spreading northward auroral forms without loosing its entity and not being suppressed by bright breakup aurora. This effect becomes apparent only due to statistical treatment and probably means that northern structures and active breakup forms have principally different sources and evolve independently. 1. Introduction During strong and/or prolonged substorm disturbances simultaneous aurora activations may be observed in the night sector near the same meridian but spaced in latitude [Kamide et al., 1977; Elphinstone, 1995; Lazutin et al., 2002]. In such events counter-streaming motion of northern auroral forms to the south and southern structures to the north are observed. Features of auroral dynamics for these cases were analyzed in [Kornilov et al., 2000; Kornilova et al., 2001]. Northern structures drifting to the equator from the polar boundary are suppose to be connected with Polar boundary Intensifications (PBIs) [Lyons et al., 1999; Kauristie et al., 2003 and ref. therein] and may be considered as breakup precursors [Kornilova, 2006; Kornilova, 2008; Nishimura, 2010]. Approaching to the prebreakup arc they initiate breakup onset. As known PBIs, and consequently northern equatorward drifting structures, are observed as well after breakup onset [Opgenoorth et al., 1996; Voronkov et al., 2004; Akasofu et al., 2010]. Nevertheless, a question on counter-streaming auroral structure interaction after breakup onset is not investigated up to now. Our paper is devoted to this study. 2. Observations For the study of aurora dynamics we used THEMIS all-aky auroral data and TV data of PGI observatories Lovozero (64.22N, 114.6E), Loparskaya (64.94N, 113.6E) and Tumanny (65.24N, 115.9E) with high spatio-temporal resolution and TV camera field of view of 180°. The methods used for TV images processing make it possible to reveal auroral structures of extremely weak intensity and to analyze their dynamics. Detailed description of the TV equipment and TV data processing used in this investigation are presented in [Kornilov, 2008; Kornilova, 2008]. IMF and solar wind plasma data as well as ground-based magnetic observations at Lovozero, Loparskaya, Tumanny and IMAGE magnetometer network data were used to estimate geomagnetic disturbance level during the events considered. A great amount of TV auroral records and both standard and filtered keograms for disturbed periods, when auroras occurred at the polar and equatorial boundaries of the auroral oval, have been analyzed. A special attention was paid to the fine structure of auroras in the spatio-temporal vicinity of the contact of counter-streaming auroral forms, when the visual contact region was situated near zenith of observatory. An example of counter-streaming structure interaction during a disturbance of 03 January 2003 is shown in Fig. 1. Polar boundary of the auroral oval and weak structures, separating from that and drifting southward are seen in keograms at 19.55 UT. Vertical arrows above and under keogram (c) mark the onset of activations in the northern and southern parts of auroral oval. In keogram (c) weak structures are enhanced by white lines, to be more noticeable. Weak structures at 19.40-19.55 UT in the south part of keograms are not accentuated as they are connected with previous activations in the north since 18.10 UT, which did not belong to keogram time interval. North structure traces approaching to the south auroral activations pass through them and keep on their southward drift. This feature is inherent the pseudo-breakup occurred at 19.50 UT as well as two subsequent activations in the south at 20.20 and 20.34 UT. An interaction between north and south auroras is the most clearly seen in time interval 20.34-20.42 UT. Northern structure activated at 20.17 UT, drifted southward, faded before the contact with southern breakup aurora (20.33 UT). Then a trace of northern structure passes through the southern breakup auroras forming weak character disturbances inside them (20.35-20.42 UT). It worth to note that observed effect is not a false one due to fog or peculiar properties of filtration that was specially controlled. Ground-base magnetic data (see Fug. Id) as well as solar wind plasma and IMF data (not presented here) show that the event under consideration was preceded by previous disturbances. Three examples of counter-streaming structure motion are given in Fig.2a-c, where standard and filtered keograms are shown. Though these events occurred at different levels of magnetic disturbance, their identical 9