Magnetic disturbances in the vicinity of synchronous orbit and the substorm current wedge: A case study

Abstract

Some features of Pi 2 pulsations and magnetic bays observed on the ground using the mid‐latitude Air Force Geophysics Laboratory (AFGL) Magnetometer Network previously have been shown to agree with ideas concerning the development of a substorm current wedge during isolated substorm onsets. In particular, the H and D component magnetic bay perturbations and the azimuths of the horizontal component of the Pi 2 polarization ellipse observed by the AFGL Network have been used to locate the approximate center and azimuthal extent of the substorm current wedge. In this paper we apply this technique to a well‐defined substorm to locate the substorm current wedge position relative to the GOES 2 and 3 synchronous satellites at L ≃ 6.6 and the nearby SCATHA satellite at L ≃ 8.1 to explain the magnetic features observed by those satellites. We find that the two satellites within the current wedge, at a position just after local midnight, simultaneously observe a dipolarization of the background field configuration beginning at the time of the substorm onset; however, the impulsive, irregular oscillations frequently observed at substorm onset are only observed by one of the satellites. The other satellite within the wedge observes a similar disturbance after a 3‐minute delay which may be attributed to an intensification or movement of currents in the downward current portion of the substorm current wedge. The satellite west of and outside the current wedge observes no significant change in the magnetic field during the event. These observations illustrate the difficulties of interpreting single‐satellite measurements of substorm effects. If magnetic data from only the satellite west of the wedge had been available, the substorm would have gone undetected. Furthermore, an incorrect substorm onset time could have been deduced from one of the satellites within the wedge.

Event study combining magnetospheric and ionospheric perspectives of the substorm current wedge modeling

“…Considering activations #2 and #3, one sees that the dipolarizations occupied the same MLT sector as the SCW, obtained in the ground magnetogram inversion, and they showed similar dynamics (see McPherron et al [], Singer et al [], and Nagai [] for previous observations). Indeed, the large bay‐like increases of H p (or B z ), a basic signature of the dipolarization (red shading), were only observed when the spacecraft entered the wedge sector in Figure (P5 and g12 in the event #2 and g13 and g14 in the event #3).…”

Comparison of magnetic perturbation data from LEO satellite constellations: Statistics of DMSP and AMPERE

“…Also, during this timeframe, magnetic measurements from LEO satellites guided researchers in studying FAC data from more distant regions. These included GOES and SCATHA [ Singer et al ., ]; ISEE [ Kelly et al ., ; Chun and Russell , , ]; and AMPTE [ Iijima et al ., 1990].…”

Substorm onset timing via traveltime magnetoseismology

“…Figure 1b is a Pi 2 event associated with a substorm onset that occurred at approximately 0655 UT on the same day, as evidenced by the AL index shown in Figure 1c. At the time of the substorm onset all ground observations presented in this letter were taken within 2 hours from midnight, and the D ‐component magnetic bays observed by mid‐latitude stations [see, e.g., Singer et al , 1985] indicate that the center of the substorm current wedge was located approximately at midnight. Figure 1d summarizes the profile of Pi 2 arrival time as a function of observatory latitude for the above two Pi 2 events in addition to two other events that have been identified by Kepko et al [2001] as BBF‐associated.…”