The February 24, 2010 substorm: a refined view involving a pseudobreakup/expansive phase/poleward boundary intensification sequence

Abstract

A substorm on February 24, 2010 was chosen for study by Connors et al. (Geophys. Res. Lett. 41:4449–4455, 2014) due to simple symmetric subauroral magnetic perturbations observed in North America. It was shown that a substorm current wedge (SCW) three-dimensional current model could represent these perturbations well, gave a reasonable representation of auroral zone perturbations, and matched field-aligned currents determined in space from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) project. The conclusion was that substorm onset was at approximately 4:30 UT and that the substorm current wedge (SCW) formed in the region 1 (more poleward) current system. Here, we examine the substorm in more detail, using ground optical data, more ground magnetic measurements, and in-situ measurements in the region of the substorm downward current by three Time History of Events and Macroscale Interactions During Substorms (THEMIS) spacecrafts. We apply magnetic inversion techniques and find that they agree with and complement optical data. We find that a sequence involving three previously categorized types of substorm-related response took place, that is, a pseudobreakup or weak expansive phase, followed by the full onset of a substorm expansive phase (EP), and in turn by a poleward boundary intensification (PBI) carrying the bulk of the SCW current. The initial activity was equatorward of that described by Connors et al. (Geophys. Res. Lett. 41:4449–4455, 2014) and began at 4:11 UT. The THEMIS spacecraft in the early morning sector detected magnetic field changes associated with the EP and PBI, aiding in differentiating them. The fuller picture suggests involvement of regions both relatively near the Earth and deeper in the magnetotail, in the overall substorm process.