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 (see additionally Fig. 1As). Over each RN± and rN± cell in Fig. 1, we mark the normalized values of I'RN±, or I'rN±, FAC intensities (in kA). Here, I'RN± = k-IRN±, where к = IRl±/IrN±, i.e. the "k" coefficient is the ratio of the FAC intensity in the input cell from generator G into the M-I system of the Northern Hemisphere to the FAC intensity in the input cell of the Southern Hemisphere. The IRi±and IrN±values are the real values of the FAC intensity of FAC on the plots of Figs. 3 As and 4 As for the 0255 UT and 0335 UT, respectively. At these instants, one observes spontaneous maxima for two EPs of Events of 1 and 2, summer and winter types, respectively. F i g u r e 1. The scheme for the current electric circuit of the substorm expansion phase in the nightside hours. The upper half shows the summer hemisphere, the lower half present the winter one. It is shown the mutual location of RN± cells, of the DRP1 partial ring current, and of DRP2 magnetospheric currents. Over the cells, the normalized FAC intensity values are presented in kA. Inside the cells, also the FAC intensity estimates (points 1 through 5) are shown . The normalization equalizes the input FAC values in the Northern and Southern Hemispheres. Fig. 1 also shows the FAC intensity estimates (in points) that are proportional to the FAC intensity numerical values. The point values are provided with the numbers (1 through 5) inside each cell (and in color in the colored version of the figures). The points were determined individually for each hemisphere. Thus, the Fig. 1 model meets three necessary requirements to the model that describes two different EP phases: the winter type in any hemisphere, and the summer type in the opposite hemisphere. These requirements are: 1) belonging of both EP phases to the season common for two hemispheres: "November-February" or "May-August", or "equinox"; 2) two EP phases are to have comparable FAC intensity values at the inputs from the generator (the I ri +~I i - i + condition), or one should propose such a normalization technique that allows one to bypass the issue of comparable, or different values of the input FACs in two hemispheres; 3) both EP phases are to occur at the above FAC maximum instant physically common for them. The latter implies that, near the selected EP maximum instants, the FAC intensity increases manyfold within ~10 minutes, and reaches the FAC level that is higher than the initial level controlled by the boundary conditions. Under such circumstances, the FAC intensity values are mostly determined by the properties of the instability producing EP. The sufficiency degree of these requirements for the typical global EP model is determined by the percent of recurrence of substorms that possess the corresponding different EP types in two different hemispheres. So far, we have studied 4 substorm pairs with the summer-type EP in one hemisphere and the winter-type EP in the other. The recurrence is 100%. 2.2. M-I coupling and M-I feedback o f two hemispheres during expansion phase The model for the electric circuit in Fig. 1 is based on the description of its skeleton (Fig. 2As) and the FAC intensity variation plots (Fig. 3As). The upper (lower) half of Fig. 1 corresponds to the model winter- ('summer-) type EP in the model Northern (Southern) Hemisphere. We note the Iri. maximum (2372 kA) in the rl- cell of the above summer hemisphere, and the IR]+maximum (600 kA) in the R1+ cell of the winter (Northern) hemisphere. These two maxima are causally related. Indeed, tracing the flows of the FACs arriving in the above input cells of two hemispheres, one can see that a strong rl- instability intensifies the FAC in the generator and in the R1+ cell, thereby producing the M-I coupling of two hemispheres. Further, however, we see the I r i . >I2+ inequality, which corresponds to the return of the FAC part from the Northern to the Southern Hemisphere. Thus, the formation of the electric circuit leads to the M-I coupling, as well as to the Ml-feedback of two hemispheres. , 2.3. Nightside FAC system collapse The above 1 ^ . > I2+ inequality, together with a small IR0+ value (100 kA), leads to the FAC intensity minimal for Rl (I ri =218 kA). The full IR1+ FAC arriving from the generator into the winter hemisphere is not used in this hemisphere, but closes onto the generator through the DRP1 ring current and rl- cell. Thus, despite the IRi+=Iri+ equality, the formation of the EP circuit presented in Fig. 1 leads to the IRi.<IRi+ inequality. There is no such a dawn>dusk asymmetry in the FAC intensity distribution within the nightside Rl and R2 in the statistical FAC model (e.g., Potemra, 1994). In contrast, such an asymmetry is a common EP property for three winter substorms that we chose randomly and addressed [Mishin et a l, 2015a, b]. We term this new phenomenon a "FAC collapse" in the dusk sector of the nightside Rl during EP in the winter hemisphere. Murphy et al. [2012]], Pellinen and Heikkila [1978] noted something similar before. The above I ri <IRi+ inequality is one of the causes for such a collapse. We note the other reason in Paragraph 2.5. 29