Hydromagnetic waves excited during an ssc

The effects of hydromagnetic perturbations that were excited by an ssc were seen at L=8.2, −12° geomagnetic latitude, 0610 geomagnetic local time in Explorer 12 energetic particle and magnetic field data, and on ground magnetograms. The entire day side magnetosphere was compressed by 2–3 RE in 2–3 min. This compression and the accompanying increase in magnetopause currents produced a 25-γ enhancement of the magnetic field at the satellite and a worldwide 45-γ enhancement at the ground. Energetic electron fluxes rose sharply at the satellite, indicating that particles moved earthward and were accelerated as the magnetic field was compressed. An additional 15-γ 2-min enhancement of the magnetic field was seen at the satellite. This pulse did not significantly enhance energetic electron fluxes and did not produce worldwide ground effects, though associated perturbations are present in some ground records. The pulse appears to represent a localized compressional magnetoacoustic wave that was excited by the rapid magnetopause motion. Finally, a damped toroidal oscillation with an initial amplitude of 26 γ, a period of 250 s, and an exponential damping time of 400 s was seen at the satellite. This oscillation could not be seen at any available ground station, the indication being that it was confined in latitude or longitude. The damping could be produced either by the coupling of energy between wave modes or by finite ionospheric conductivity. The wave period agrees with predictions if the density of plasma on the field line varies with radial distance as r−6, with ρ=4 to 12 ions/cm³ at the equator. An initial energy input of 4 × 1020 dL to 2 × 1021 dL ergs can produce the observed wave amplitude, if plasma at all longitudes between the L and the L + dL shells is involved in the oscillation.