GROUND SATELLITE-OBSERVATIONS OF PC-1 MAGNETIC PULSATIONS IN THE PLASMA TROUGH

An analysis of concurrent Pc 1 pulsation activity (0.2-0.6 Hz) recorde d on the ground at Mawson, Antarctica (70 degrees 8 magnetic latitude (MLAT); 19 degrees E magnetic longitude (MLONG); L=8), acid on board t he Viking polar-orbiting satellite, when the spacecraft was located ne ar apogee (13.5x10(3) km) from 50-77 degrees MLAT above the northern i onosphere, shows that simultaneous pulsations were observed only when Viking's conjugate point was within 60-70 degrees S MLAT and 30 degree s E-33 degrees W MLONG, an extent of about 1000 km in latitude and 170 0 km in longitude. Spectral analysis confirms that the waves responsib le for these pulsations are electromagnetic ion cyclotron (EMIC) waves that have propagated to the spacecraft and ground from the geomagneti c equates. For the intervals when the waves were on field lines above and equatorward of Mawson, convective EMIC wave modeling shows wave gr owth is dominant below the equatorial He+ gyrofrequency. Waves generat ed on field lines poleward of Mawson exhibit frequencies above the equ atorial He+ gyrofrequency. These propagate to Mawson, most likely thro ugh a purely proton plasma rather than a multi-ion environment. Freque ncy shifts in the Pc 1 activity at Mawson appear to be directly linked to solar wind velocity and flux variations measured by IMP 8. For cer tain intervals these linked observations are consistent with an interp retation based on the velocity and flux changes altering the radial po sition of the magnetopause through pressure balance considerations. Th is, in turn, changes the magnitude of the ambient magnetic field in th e equatorial plasma trough and consequently the ion gyrofrequency and EMIC growth rate. Pc 3-5 activity was recorded at Mawson in conjunctio n with the Pc 1 frequency shifts and in association with rapid B-IMF v ariations. The changes in the temperature anisotropy and energy of the resonant ions in the plasma trough, which are causing the Pc 1 emissi on changes, are associated with the entry of dayside Pc 3-5 pulsation energy into the dayside magnetosphere.