Testing a two‐loop pattern of the substorm current wedge (SCW2L)

Abstract

model revealed systematic discrepancies between the observed and predicted amplitudes, which suggested us to include additional region 2 sense currents (R2 loop) earthward of the dipolarized region (SCW2L model). Here we discuss alternative circuit geometries of the 3-D substorm current system and interpret observations of the magnetic field dipolarizations made between 6.6 R E and 11 R E , to quantitatively investigate the SCW2L model parameters. During two cases of a dipole-like magnetotail configuration, the dipolarization/injection front fortuitously stopped at r ∼ 9 R E for the entire duration of ∼ 30 min long SCW-related dipolarization within a unique, radially distributed multispacecraft constellation, which allowed us to determine the locations and total currents of both SCW2L loops. In addition, we analyzed the dipolarization amplitudes in events, simultaneously observed at 6.6 R E , 11 R E and at colatitudes under a wide range of magnetograph conditions. We infer that the ratio I 2 ∕I 1 varies in the range 0.2 to 0.6 (median value 0.4) and that the equatorial part of the R2 current loop stays at r > 6.6 R E in the case of a dipole-like field geometry (BZ 0 > 75 nT at 6.6 R E prior to the onset), but it is located at r < 6.6 R E in the case of a stretched magnetic field configuration (with BZ 0 < 60 nT). Since the ground midlatitude perturbations are sensitive to the combined effect of the R1 and R2 sense current loops with the net current roughly equal to I 1 − I 2 , the ratio I 2 /I 1 becomes an important issue when attempting to monitor the current disruption intensity from ground observations.

Investigations of the auroral luminosity distribution and the dynamics of discrete auroral forms in a historical retrospective

“…Thus there emerged in the scientific literature on model descriptions of substorm currents also other concepts of current systems (see, e.g. Sergeev et al, 2014). The 3-D magnetospheric current system is controlled yet by several other sources and proves therefore to be quite complex.…”

Aspects of magnetosphere–ionosphere coupling in sawtooth substorms: a case study

“…In our sawtooth substorms, both phenomena (near-Earth current disruption and magnetotail reconnection) are strongly related in the meaning that one leads to the other. Thus we suggest the following scenario of magnetospheric processes: (i) near-Earth current disruption leading to activation of the SCW with its "inner and outer loops" (see Sergeev et al, 2014), which is followed by (ii) activation of magnetic reconnection at the NENL (reconnection of lobe flux) with associated plasma injection. On the ionospheric level, this two-stage process is manifested as enhancements of (i) the auroral electrojets (via the Bostrøm type I and II systems) and (ii) the PCN index (see Fig.…”

“…1, we extend the standard two-loop model of the SCW (Sergeev et al, 2014) when we specify the inner loop connecting the partial ring current (PRC) and the ionosphere (EEJ in auroral oval south regime) via the Bostrøm type II current system. This is essential for a proper description of M-I coupling during substorm activity.…”

Transitions between states of magnetotail–ionosphere coupling and the role of solar wind dynamic pressure: the 25 July 2004 interplanetary CME case

“…The cyclical behavior is closed by return (recovery) to the initial state of loading of magnetic energy in the tail lobes, after the episode of enhanced energy dissipation in the auroral ionosphere. The substorm activity may be described in terms of activations of basic current systems in the magnetosphere-ionosphere system consisting of outer and inner loops (Sergeev et al, 2014). The basic elements of the two-loop current system of magnetosphere-ionosphere (M-I) coupling and their relation to auroral electrojets were identified in the early phase of substorm research (Bostrøm, 1964(Bostrøm, , 1967McPherron et al, 1973;Yasuhara et al, 1975;Bostrøm, 1977).…”

“…This model is characterized by (i) an outer loop connecting the cross-tail current disruption and corresponding electrojet activity in the northern part of the auroral oval (the Bostrøm type I azimuthal loop) and (ii) an inner loop connecting the near tail (PRC) and the southern part of the oval by Bostrøm type II current systems (meridional loops) maximizing at dusk and post-midnight MLTs. Our focus on the closure currents in the northern and southern sections of the auroral oval represents an extension of the two-loop model of Sergeev et al (2014) (see also Yang et al, 2012 andBirn andHesse, 2014). Activations of the inner loop, which we refer to as Bostrøm type II, in the phase of plasma braking and diversion in the near tail during plasma intrusion events (Earthward-moving BBFs; see Baumjohann et al, 1990), are described in, e.g., Yang et al (2012) and Birn and Hesse (2014).…”