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

Abstract

Recent quantitative testing of the classical (region 1 sense) substorm current wedge (SCI) 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 ( B Z 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 B Z 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.