Physics of auroral phenomena : proceedings of the 39th annual seminar, Apatity, 29 February-4 March, 2016 / [ed. board: N. V. Semenova, A. G. Yahnin]. - Апатиты : Издательство Кольского научного центра РАН, 2016. - 167 с. : ил., табл.

I.V. Despirak et al. The distributions of the month substorm number during the 23-th cycle is shown in the left panels, and during the 24-th solar cycles - in the right panels. It is seen that the “polar” substorm behavior was opposite to the “expanded” substorm behavior. We downloaded the PC-index values before the onset of all the types of substorms, averaged for a 1.5 hours’ interval prior to the moment of the substorm onset. PC-index is an empirical index of the magnetic activity in the polar cap, it is aimed to monitor the polar cap magnetic activity generated by the solar wind parameters. It is based on the data from a single near-pole station (Thule or Vostok). It is known, that PC-index values best correlated with the azimuthal component of the interplanetary electric field. In Fig. 2, there are presented the histograms of the PC- index values observed before the onset of the “polar” (P, green lines), ’’expanded” (E, red lines) and “usual” (U, blue lines) substorms. 1 2 0 - i 100 - 80 - 60 - 40 - 20 - 80 - | 60 4 0 - 2 0 - 2 0 0 3 -2 0 0 9 100 -1 so - 60 - 40 - I 20 -J u A 1999 -2000 flL 2012-2013 Figure 2. The PC- index values before the substorm onsets in 1995-9996 (a), 1999-2000 (b), 2008-2009 (c), and 2012-2013years (d) Type of substorm 1995-1996 1999-2000 2008-2009 2012-2013 “expanded” 1.5±0.7 2.0±0.8 1.1±0.8 1.6±0.9 “polar” 0.7±0.4 0.77±0.6 0.4±0.3 0.52±0,5 Table 1. The averaged values of the PC-index before the onsets of the “polar” and “expanded” substorms for two solar cycle maxima (1999-2000 and 2012-2013), and two solar cycle minima (1995-1996 and 2008-2009). 9