Ground satellite observations of Pc 1 magnetic pulsations in the plasma trough

Abstract

An analysis of concurrent Pc 1 pulsation activity (0.2–0.6 Hz) recorded on the ground at Mawson, Antarctica (70°S magnetic latitude (MLAT); 19°E magnetic longitude (MLONG); L=8), and on board the Viking polar‐orbiting satellite, when the spacecraft was located near apogee (13.5×10³ km) from 50–77° MLAT above the northern ionosphere, shows that simultaneous pulsations were observed only when Viking's conjugate point was within 60‐70°S MLAT and 30°E–33°W MLONG, an extent of about 1000 km in latitude and 1700 km in longitude. Spectral analysis confirms that the waves responsible for these pulsations are electromagnetic ion cyclotron (EMIC) waves that have propagated to the spacecraft and ground from the geomagnetic equator. For the intervals when the waves were on field lines above and equatorward of Mawson, convective EMIC wave modeling shows wave growth is dominant below the equatorial He+ gyrofrequency. Waves generated on field lines poleward of Mawson exhibit frequencies above the equatorial He+ gyrofrequency. These propagate to Mawson, most likely through a purely proton plasma rather than a multi‐ion environment. Frequency 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 certain intervals these linked observations are consistent with an interpretation based on the velocity and flux changes altering the radial position of the magnetopause through pressure balance considerations. This, in turn, changes the magnitude of the ambient magnetic field in the equatorial plasma trough and consequently the ion gyrofrequency and EMIC growth rate. Pc 3–5 activity was recorded at Mawson in conjunction with the Pc 1 frequency shifts and in association with rapid BIMF variations. The changes in the temperature anisotropy and energy of the resonant ions in the plasma trough, which are causing the Pc 1 emission changes, are associated with the entry of dayside Pc 3–5 pulsation energy into the dayside magnetosphere.