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.

А. V. Nikolaev et al. 1989] and its background magnetic field stretching parameter (RCF).To neglect the asymmetry of SCW with respect to neutral sheet and midnight meridian, we fix FACs central longitude at midnight and perform calculations on 2009/09/05 at 08:00:00 UT, when the dipole tilt angle value was ~0. In addition, the transverse current spread (D0), scaled as D2 ~ R3/2, was not allowed to exceed 2 Re at tailward distances greater than R = 8 Re, where its half­ thickness D was equal to 0.5 Re. The RTj is fixed at 15 Re. In addition we require both current loops span the same longitudinal sector (i.e. Pw and Pe values equal for both wedges).Taking into account a complicate topology of R2 duskward current, we reproduce its extreme shapes (see Fig. 2a) as concave and convex contours I and II and calculate magnetic radial profiles along X axis (Y=0) for three different SCW2L configurations (Fig. 2b, I, II and red solid curves). The total current intensities was set in this example to be Ij = 1 MA and I2 = 0.5 MA, while Pw and Pe for both loops was kept fixed at 155° and 205° SM Lon, correspondingly. As seen from Fig. 2b, difference between magnetic radial profiles of I and II curves is significant, so we remove its curvature and use simple straight- line connection between FACs (red wedge at Fig. 2a). Red solid line plotted at Fig. 2b shows magnetic field disturbance generated by R1 plus R2 currents. Ionospheric footprint displacement due to SCW Choosing points of the neutral sheet as starting locations in the night side magnetosphere, we trace magnetic field lines to ionospheric heights (R = 1.02 Re) two times: first time we use standard T89 model [Tsyganenko, 1989] and second time, combination of T89 and SCW2L models. The latitudinal and longitudinal difference between corresponding neutral sheet footprints is measured by geocentric angle expressed as acos(* ) where R = 1.02 Re, and [X, Y, Z] is the footprint coordinates [GSM] obtained by two trace procedures. Fig. 3 graphically illustrates (1) amplitudes of mapping distortions (by color), (2) R1 and R2 loop configurations in XY plane and (3) radial distance to R2 cross-tail current (RT2 = 6 Re). Corresponding current intensities are L = 1 MA Ionospheric footprints displacement due to SCW ■3 -7 -12 -16 -20 ^OSM t Fig. 3 View from the North. Neutral sheet locations traced to ionosphere with addition of the substorm current wedge magnetic field. Color indicates amplitudes of ionospheric footprints deformation after adding SCW2L model in terms of geocentric angle. Location of R1 and R2 loops are also presented. The calculations performed for : 205 SM Lon., RT, = 15 Pw = 155° SM Lon, Pe Re, RT2= 6 Re. Ionospheric Mapping with/without SCW and I2 = 0.5 MA, which can be met during strong and rather rare substorms. In order to visualize ionospheric footprint shifts, colored in Fig. 3, we map the set of equidistant neutral sheet points (drawn at Fig. 3 as azimuthal arcs) to nightside ionospheric plane and illustrate it on Fig. 4. Red lines indicate arcs (with radius of curvature covering range of distances from R = 4 Re to R = 20 Re) traced with IGRF plus T89 models, while the green ones show the same arcs, mapped with addition of SCW2L model. The square and cross symbols correspond to upward and downward FACs footprints. Red and green contours together with Fig. 3 graphically illustrate the pattern of ionospheric distortions, consisting o f three specific areas. The first one is the region, localized between equatorial R1 and R2 currents inside SCW azimuthal sector, where footprints poleward shift reach its maximum value when approaching the R1 loop currents (red area at Fig. 3). The second ones form a rotational type of displacement in the region, where the magnetic field lines explicitly twisted by the FACs. The R2 field-aligned currents have a smaller contribution to the mapping distortion, because they act in the region of strong background magnetic field and their intensity is lower than that, flowing in R1 loop. The third black doted area at Fig. 3 corresponds to the region of weak magnetotail field, strongly disturbed by the magnetic field o f R1 equatorial current. The O- type field lines appear at those locations and prevent connection between ionosphere and plasma sheet, so we excluded that region from analysis. In addition, vortices centered at the points o f FACs projections are not analyzed because the small-scale SCW signatures cannot be described by highly idealized SCW2L model, which is only suitable for the diagnostics of large-scale magnetic field changes. Fig. 4 Ionospheric pattern of the equidistant neutral sheet lines projections obtained without (red) and with (green) addition of the Substorm Current Wedge magnetic effects. Footprint displacement depending on SCW parameters Current intensities play an important role in substorm-time magnetospheric diagnostics, because R1 and R2 wedges can both enhance and compensate for each other magnetic effects in different observational locations. The ground-based magnetometer 52