A statistical correlation of Pc5 pulsations and solar wind pressure oscillations

The SHARE high frequency (HF) radar in Antarctica is used to compare ionospheric plasma flow oscillations in the Pc5 frequency range with low-frequency oscillations in the solar wind pressure measured by the ACE spacecraft. Ten different days in 2000 and 2001 are analysed with respect to different frequencies and geomagnetic latitudes. Both data sets are bandpass filtered and a complex demodulation technique is used to calculate the correlation in each band. On a number of occasions the wave packet structure of the Pc5 pulsations is in good or excellent agreement with the wave packet structure of the solar wind pressure oscillations. This strongly suggests that the oscillations were directly driven by the solar wind. Particularly good correlation is found in the frequency band 0.8-1.2 mHz. Pulsations in this frequency range are hard to reconcile with the magnetospheric cavity mode model. We conclude that, at least on some occasions, Pc5 pulsations may be directly driven and the magnetosphere cavity/waveguide then assumes a more passive role.