Physics of auroral phenomena : proceedings of the 36th Annual seminar, Apatity, 26 February – 01 March, 2013 / [ed. board: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2013. - 215 с. : ил., табл.

The magnetospheric magneticfield deformation: Effects o f double-loop Substorm Current Wedge inside the azimuthal sector of two wedges of opposite polarities observes bay-like variations, characterized by Ii-I2, while spacecraft located in between R1/R2 loops registers cumulative current effects Ii+I2. The intense currents obviously lead to the greatest magnetic field changes (according to Biot-Savart law), particularly in the area lying between wedges (red colored region at Fig. 3) where the effects o f R1 and R2 current loops are added. Our study focuses on the contribution of SCW2L parameters (such as I 1; RCF and I2/Ii) to mapping distortions, so we fixed RT2 = 6 Re in the region of strong background magnetic field and examined the latitudinal footprints shift (plotted at Fig. 5d-f) for the set of equatorial points (Fig. 5b) lying in the center of SCW azimuthal sector (Y=0, Z=0). Calculations performed for moderate (I( = 0.5 MA, Fig. 5d), strong (I] = 1 MA, Fig. 5e) and extremely strong (I, = 2 MA, Fig. 5f) substorms showed that the poleward footprints expansion rather small in first case (~ 2-3° CGLat), increases in the second case (~ 5 - 6° CGLat) and maximizes in third case (~ 9° CGLat). The enhanced R2 current (I2/Ii > 0.5) decreases the amplitude of maximal latitudinal displacement by < 20% and causes small equatorward footprint shift in vicinity of R2 current latitudes. This effects are explained by Fig. 5c illustrating the Bz magnetic profile built with SCW2L model (I[ = 1 MA) along the T89 model field line starting from X = -10 Re [GSM]: in vicinity of equatorial plane magnetic field is enhanced by SCW-related depolarization (ABz>0), but in tail lobes it is depressed by nearby R2 FACs (ABZ< 0), thus magnetic field lines is deformed as shown in Fig. 5a. The red curve gap which is visible in Fig. 5f is the region, where the strong R2 equatorial current (I2 = 1 MA) forms the loop magnetic field line and prevent connection between ionosphere and plasma sheet. As for the background magnetic field stretching parameter (RCF), it slightly varies the footprints ALat by ~ 1-2° CGLat as seen from Fig. 5e, where black lines go higher than colored ones. Relationship between SCW and auroral streamers From a wide range of auroral manifestation during substorm expansion phase we can distinguish North-South auroral forms (NS) emerging within auroral bulge. Henderson et a l, [1994] schematically illustrated the occurrence of north-south auroral forms in the active poleward region of auroral bulge (termed as “traversing arc”) in vicinity of the surge head. Authors showed that some o f NS are ejected from the intensifying traversing arc, drift equatorward, then split and continue its propagation westward/eastward (see Fig. 9.2 in Henderson et al., 1994) with the tendency to rotate clockwise in the region lying nearby WTS. Results obtained from spacecraft observations have been supported by Nakamura et al., [1993] who compiled ground-based optical observations of eight all-sky TV cameras and illustrated similar dynamics of the poleward boundary and NS. The conjunction of auroral streamers with the earthward moving transient bursty bulk flows (BBFs) was discussed in e.g. Nakamura et al., [2001], Henderson et al, [2012], Lyons et al., [2012]. Concentrated current leaving the ionosphere generates vortex-like magnetic field, which twist nearby field lines and causes their footprints rotate around location of FACs. To illustrate it we mapped to the ionosphere the neutral sheet locations presented in Fig. 6a as narrow radially- aligned structures morphologically similar to BBFs (in “zero” approximation). The color changes in the direction of BBF movement along straight trajectories in plasma sheet. Black north-south aligned strips in Fig. 6b reflects ionospheric BBFs paths calculated with IGRF plus T89 model, while colored ones reflect corresponding trajectories obtained by addition o f SCW2L model with I] = 1 MA, I2 = 0.5 MA, RT2=6 Re and RCF=6. Predicted NS auroral forms are divided into two groups: first one, reflects BBFs moving in the FAC vicinity where magnetic field configuration is highly sensitive to enhanced SCW-related By-magnetic component responsible for the twist of the magnetic field line; in the second group neutral sheet locations in a central SCW longitude are traced along field lines disturbed by strong positive Bz magnetic component, which shifts ionospheric footprints poleward. FlaldUn« topology (tracad point X**10M) ■ ■ ■ 12Л1• 0.3 (RCF-6) <s С1 О »2/l1■ 0.8 (RCF»©) ----------------- 12 /11 • 0.3 (RCF-O) 12/11■ 0.8 (RCF-O) X gsm , Re 11 ■ 2 MA , RCF » 8 J* / Fig. 5 Footprints shifts for the points lying in the X axis (Y=0) in the XY plane: a) XZ cut of the SCW FACs and the shape of field lines starting from X = -10 Re; c) Bz magnetic radial profile obtained from SCW2L along field lines at a) plot; d) latitudinal shifts for moderate substorms (Ij = 0.5 MA) for I|/I2 = 0.3 and 0.8; e) latitudinal shifts for stronger events for two values of I]/I2 and RCF; f) the same as in d) but for I, = 2 MA, RCF = 8. 53