Abstract
Abstract. We study compressional pulsations in Pc5 frequency range observed in the dawn-side at distances of about 10 RE , close to the magnetic equator. We use data obtained during two events of conjunctions between Equator-S and Geotail: 1000–1700 UT on 9 March 1998, and 0200–0600 UT on 25 April 1998. In both events, pulsations are observed after substorm activity. The pulsations are antisymmetric with respect to the equatorial plane (even mode), and move eastward with phase velocity close to plasma velocity. The pulsations tend to be pressure balanced. We also discuss possible generation mechanisms of the pulsations.Key words. Magnetospheric physics (magnetospheric configuration and dynamics; MHD waves and instabilities; plasma sheet)
Highlights
Strong compressional Pc5 pulsations, i.e. variations in the magnetic field magnitude with periods of typically about 10 minutes, are commonly observed in the outer magnetosphere at low geomagnetic latitudes
The Equator-S and Geotail satellites are well suited for studies of these pulsations because their orbits are close to the equatorial plane and cover large L distances
Compressional Pc5 pulsations are most often observed at large L distances, L ≥ 8, and there is a vast amount of data and studies related to this subject
Summary
Strong compressional Pc5 pulsations, i.e. variations in the magnetic field magnitude with periods of typically about 10 minutes, are commonly observed in the outer magnetosphere at low geomagnetic latitudes. The following generation mechanisms have been suggested for the compressional pulsations: plasma anisotropy (Hasegawa, 1969), pressure gradient, together with gradient and curvature in ambient magnetic field (Cheng and Qian, 1994; Chen and Hasegawa, 1991), and bounce-resonant particles (Southwood, 1976). Most of these mechanisms predict that in a high-β plasma, the mode that will be generated first is antisymmetric with respect to the magnetic equator. From Geotail we use 12-sec averaged data from the Geotail magnetic field (Kokubun et al, 1994) and low energy particle experiment (Mukai et al, 1994)
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