A global pulsation event with conjugate study

Abstract

On 17 July (day 198), 1982 a global long period pulsation was recorded over an extended array in the Northern Hemisphere and by magnetometers at the conjugate stations of Halley Bay and St Anthony, between 10:30 and 11:10 U.T. The pulsation appears to be simultaneously driven and highly damped, lasting for approximately five cycles with a period of about 450 s. Significant phase variations appear across the array and there are strong indications of an enhancement in amplitude of toroidal oscillations in the vicinity of the boundary of open/closed field lines. Analysis of the amplitude and phase variations between the stations suggests that the conjugate field line was oscillating in a fundamental quarter wave standing mode. Using whistler data, an estimate of the plasmapause position was obtained which indicates that the Halley/St Anthony field line was located in the innerplasmatrough. However, the anomalously long period and global behaviour suggests that the conjugate stations were situated some distance from the centre of the disturbance. Analysis of ISEE 3 data prior to the event indicated a doubling of solar wind pressure which may be correlated with the onset time of the event. In addition, a drop in solar wind velocity and switching of B z during the event indicate the possibility of a significant expansion of the magnetosphere with resultant rarefactional waves, the effects of which may be seen in the ground magnetograms towards the end of the event. It is suggested that this global disturbance was driven by large changes in solar wind conditions.