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.

“Polar" and “high latitude" substorms and solar wind conditions The concept of the westward electrojet “center” (the region of the highest currents) is often used for latitudinal positioning of the westward electrojet, since it occupies a large spatial area during the substorm expansion phase and can be inhomogeneous [26]. The method for electrojet “center“positioning is described in detail in [9]. Let us note that we consider a “high-latitude” substorm if it starts at the auroral zone and the westward electrojet “center” is observed at LYR or NAL stations during the maximal substorm phase, i.e., at 75.12° (78.9°) or 75.25° (78.2°) geomagnetic (geographic) latitude. Results Both types of substorms -“polar” and “high-latitude”—were compared with the interplanetary conditions, i.e., the presence/absence of high speed solar wind streams, the presence of a geomagnetic storm, etc. The examples of considered events are presented in Fig. 1. 8 *3 10 0 0 t- ' 10800 i X § 600 > 1 1 400 w £ -400 8 1 «00 Q 0 „ 4.0E+5 Я O.OE +0 « 8 * * 4 40 ¥ П Ы о н i V £ 4 * 1 >M 20 10 0 10 0 %0 \ 600 400 400 | s a 1.2E+S 8.0E+5 4.0E+5 O.OE +O * я «Ь * 40 "High-latitude” substorms 1 2 3 4 5 6 7 January 1995 b "Polar" substorms 2 3 4 5 6 7 8 January 2007 a Figure 1. Solar wind and IMF parameters (BT Bz, V, Vx, N, T, P) and the SYMN/H index for two high speed streams on January 1-6, 2007 and January 2-8, 1995. Top-down: magnetic field magnitude and the IMF Bz component, the stream velocity V, the X component of the solar wind velocity, the density N, the temperature T, solar wind dynamic pressure P, and the geomagnetic index SYMN\H. Boundaries of the high speed stream (HSS) are shown by gray rectangles. The onset times of “polar” and “high-latitude” substorms according to the IMAGE data are marked by the vertical solid and dashed lines, respectively. Fig. 1 shows the solar wind and IMF parameters for two high speed streams, on January 1-6, 2007 and January 2-8, 1995. High speed streams are shown in the both cases by gray rectangles. The onset times of “high latitude” and “polar” substorms are superimposed on these data according to the IMAGE data; they are shown by the solid and dashed lines, respectively. Fig. la presents the solar wind conditions during the observation of a “polar” substorm, and Fig. 2b shows them during the observation of “high-latitude” substorms. In the first case (January 1-6, 2007), “polar” substorms occurred on January 5, 6, 7, and 8, i.e., at the end of a high speed stream and after it, when the solar wind velocity decreased from the high values to low ones. The solid curve shows a “high-latitude” substorm that was observed on January 3,2007. Fig. lb presents solar wind conditions during “high-latitude” substorms; they occurred on January 2, 3, and 7, i.e., during the high speed stream on January 2-8, 1995; after the stream passed, during the solar wind velocity drop, a “polar” substorm was observed. According to the SYMN\H index, no geomagnetic storm was observed during 11