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.

V.M. Mishin et al. 2.4. Role o f the DRP1 ring current in producing the M-I current system o f two hemispheres Comparing the numerical values of 1^. = 511 kA and IrI. =2372 kA shows a strong Ir 2 - » I ri- inequality. We observed such a strong inequality only in one case, but the sign and the value of the inequality ~ (10 -=-10 ) kA persisted in all the addressed substorms. These inequalities provide a numerical estimate o f the DRP1 partial ring current contribution to producing the M-I coupling of the common current system in two hemispheres. 6 April 2000 Figure 2. Examples of the FAC density distribution in the Northern Hemisphere polar ionosphere. Solid/dotted lines show the upward/downward FAC. In the MLT night half, the RN± symbols mark the centers of the mesoscale cells. On Maps 2 and 4, the downward and upward FACs in Rl are located symmetrically relative to midnight. On Map 1, one can see the dusk>dawn assymmetry (the upward FAC distribution is twisted counter-clockwise). Maps 3 and 5 provide the examples of the clockwise twisting. 2.5 Azimuthal twisting and untw isting o f the FAC system Fig. 2 shows the maps of different types of the FAC distribution in the addressed Events 1 and 2. A special difference in this type FAC distribution from the expected FAC distribution in the Iijima and Potemra model is a signature for each type. In this model, the distribution of the nightside FAC density and intensity is approximately symmetrical relative to the meridian separating the downward and upward FACs. Due to the restricted paper scope, we describe the signatures for each type here referring only to R l, although similar signatures are also observed in R0 and R2. Fig. 2 presents the examples of these signatures in Rl. They are the following. Type 1, 0203 UT: one observes the dusk>dawn asymmetry in the distribution of the FAC density and intensity, and counter-clockwise twisting o f the upward FAC distribution in the nightside Rl. Type 2, 0208 UT: there occurs an I-P-type FAC distribution in the nightside R l. One can see two weak cells of the substorm current wedge, without the dawn/dusk asymmetry and the corresponding twisting. Type 3, 0216 UT: one can see the prevalence o f the downward FAC in the premidnight and postmidnight sectors in the nightside R l as a result o f the FAC distribution clockwise twisting. The twisting leads to an upward FAC westward displacement in the Rl premidnight sector, which results here in the partial collapse (intensity decrease) of the upward FAC. Type 4, 0300 UT: in the nightside Rl (and in R2), there was established a FAC distribution of a strong intensity and of the 1-P model type without the dawn- dusk asymmetry at the EP peak. Type 5, 0335 UT: signatures o f clockwise twisting o f the FAC distribution emerged again in the nightside R1-. Note that the term "twisting" does not assume the process in time, but the result o f reconfiguration o f the FAC spatial distribution. The physics o f the "twisting” phenomena is yet to be studied. As a possible version, we note that similar phenomena may be created by local processes of the tail extension and dipolarization during substorms. Each of these processes produces a strong (~106 A) X-current in the tail plasma sheet [Lui and Kamide, 2003]. We assume that this current density is inhomogeneous along the X-axis, and it is this that produces the X-current divergence, i.e., a FAC area extended on the X-axis along the inhomogeneity. The direction of such a FAC depends on two factors. The first factor is the tail extension, or dipolarization. The other factor is the X-current gradient direction in the inhomogeneity producing the twisted FAC area. Four combinations of these two factors are possible. They are the following: (1) "the tail extension and the above gradient Earthward", (2) "the tail extension and the above gradient off-Earth", (3) "the tail magnetic field dipolarization and the above gradient Earthward", (4) "the tail magnetic field dipolarization and the above gradient off-Earth." Combination 1 (2) produces the upward (downward) FAC in the ionosphere, where the tail X-current closes. Combination 3 (4) produces the downward (upward) FAC in the area, where it is implemented. Thus, the four combinations describe the clockwise and counter-clockwise twisting presented in Fig. 2, both at the tail local extension and at the tail local dipolarization. 30