Global magnetospheric-ionospheric oscillations initiated by a solar wind pressure impulse

Abstract

We present simultaneous observations of long-period (~1 hour) global magnetospheric-ionospheric oscillations with multiple spacecraft and ground-based instruments. These oscillations occurred following a major increase in the solar wind dynamic pressure. When the solar wind pressure impulse impinged on the magnetosphere, oscillations of energetic plasma particles in the ring current region were excited. The strongest oscillations came from electrons in the energy range of 75-225 keV with periods of 55-80 min. Ground magnetometers measured periodic (~1 hour) enhancements of ionospheric currents from the auroral to equatorial latitudes. However, the solar wind pressure and IMF in this event did not show variations similar to the energetic particle oscillations and/or ground magnetometer deviations. We suggest that the magnetosphere has an intrinsic period of ~1 hour during quiet times. The magnetospheric oscillations with this period can be initiated by a solar wind pressure impulse. After the initiation the solar wind no longer plays a role in the subsequent evolution of the magnetospheric oscillations