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.

FIELD-ALIGNED CURRENT DYNAMICS DURING TWO SUBSTORMS OF SUMMER AND WINTER TYPES AND MODEL FOR THE ELECTRIC CIRCUIT OF THE MAGNETOSPHERE-IONOSPHERE SYSTEM OF TWO HEMISPHERES V.M. Mishin, V.V. Mishin, M.A. Kurikalova, Yu.A. Karavaev, and O.I. Berngardt {Institute o f Solar- Terrestrial Physics o f Siberian Branch o fRussian Academy o f Sciences ) Abstract. Based on the time series from maps of field-aligned current (FAC) distribution in the ionosphere, we developed an empirical scenario for the substorm expansion phase (EP) in two hemispheres. Its peculiarities are: 1) We took into account mesoscale cells with the FAC density local maximum inside each Iijima and Potemra (I- P) Region, which augmented the spatial resolution two- or threefold. 2) We described two types of the FAC distribution in the nightside polar ionosphere, observed during the substorm EP in the winter and summer hemisphere, respectively. These two types start simultaneously in two hemispheres, but in different MLT-sectors of the nightside Region 1 that are separated by ~6 MLT. 3) We revealed that the global magnetosphere-ionosphere (M-I) feedback instability in the summer hemisphere premidnight sector serves as an initiator and organizer of the global EP. 4) We designed a schematic model for the electric circuit of the disturbed nightside M-I system. The model describes the above distributions of FAC, ionospheric currents, and partial ring current. We note the contribution of the ring current to the M-I feedback instability evolution. 1. Introduction The current scenarios for magnetospheric substorms are based on satellite measurement data, as well as on the ground-based measurements [e.g., McPherron et al., 1973; Baker et al., 1996; Lui et al., 1996; Angelopoulos et al., 2008; Akasofu, 2015]. They address a typical substorm as a global phenomenon, where signatures of the hemisphere asymmetry are established facts, and the assymetry manifestations are significant [e.g., Ostgaard et al., 2011; Reistad et al., 2014; Laundal and Ostgaard, 2009; Knipp et al., 1993; Lu et al., 2011]. However, the scope of the accumulated database from the ground-based measurements in the Southern Hemisphere is tenfold smaller, than that for the Northern Hemisphere. Thereupon, we note that the known manifestations of the typical substorm asymmetry do not affect the fundamental signatures of the typical substorm expansion phase (EP). On the other hand, there is individual evidence that the substorm current systems differ dramatically in the Earth's two hemispheres (at least, near the EP maximum times) [Mishin et al., 2015a], It is the summer hemisphere, where EP manifests itself like a spontaneous manyfold increase in the downward field-aligned current (FAC) in the R1 premidnight sector of the summer hemisphere. Hereinafter, we denote this site as "Rl- cell." The impulse lasts for -10 minutes. In contrast, in the winter hemisphere, in this sector, one observes the FAC collapse, although, in the adjacent Rl postmidnieht sector, one simulteneously observes the EP signatures. The above two sectors constitute the most active EP interval -(06-18) MLT [Kissinger et al., 2012]. The centers of these two sectors of the winter hemisphere are separated by 6 MLT. The FAC directions in the winter hemisphere two sectors are opposite. In the summer hemisphere premidnight sector, one observes the signatures of the M-I feedback instability that are absent in the winter hemisphere. Thus, according to the empirical data from Mishin et al. [2015a], the substorm in two hemispheres is initiated and driven from the above Rl - cell of the summer hemisphere. We developed this scenario from the data on the pair of substorms observed in the Northern Hemisphere, one during the summer season, whereas the other was observed during winter season. Mishin et al. [2015c, Associated paper] find out the applicability of this scenario to substorms of the equinox season. This paper is the continuation of this study. We use the designations, conclusions, and figures from the Associated paper referring to the latter as "As- paper." The figures are denoted as "NAs Fig.”, where N is the Figure number. We use the quantitative data from the As-paper to design the schematic diagram for the EP electric circuit. The diagram combines the pair of the winter- and summer-type EP events denoted as «Events 1 and 2», respectively, in the As-paper. Here, "winter" and "summer" do not denote the local season, but rather the substorm EP content described in the As-paper. Fig. 2 in the As-paper provides the skeleton of the above schematic model. We need its description in the As-paper to understand the further text. 2. Model for the M-I system electric circuit during EPs of Events 1 and 2 2.1 To combine two EPs within a common schematic model for the substorm global EP, we chose Events 1 and 2 which are an amazing, but typical of the equinox, example. In this example, the EP regime changes fundamentally from the above "winter" to the above "summer" type for two hours, at transition from the (02-03) UT interval to (03- 04) UT. Fig. 1 provides this combining model. The figure was obtained based on Fig. 2As that is the model skeleton (without numbers). The terms RN± and rN± specify the position of each cell in the polar regions o f two hemispheres *P hysics o f Auroral P henom ena”, Proc. XXXVIII A nnu al Seminar, A patity, pp. 28-31, 2 0 1 5 © Kola Science Centre, Russian Academy of Science, 2015 28 Polar Geophysical institute