Ultra-low-frequency waves and associated wave vectors observed in the plasma sheet boundary layer by Cluster

Abstract

Waves in the Pc1-Pc2 frequency range (0.1-5 Hz) are studied using Cluster magnetic field data. In the plasma sheet boundary layer, Cluster observed harmonically related waves with the fundamental near the local proton cyclotron frequency (Ωp). These waves had components both parallel and perpendicular to the local magnetic field (B0). Application of the wave telescope yielded the full wave vector (k) of the waves and showed that they propagated nearly perpendicular to B0. Associated with the waves were two counterstreaming ion beams with a relative velocity of approximately 4000 km/s. During wave activity, the tailward streaming beam increased in energy flux, and subsequently, energy flux increased in directions perpendicular to B0. We suggest two possible sources for the waves: inverse Landau resonance with an accelerated electron beam and an electromagnetic ion/ion cyclotron instability. The change in the ion distribution suggests these waves could contribute to the formation of the hot protons of the central plasma sheet. Copyright 2008 by the American Geophysical Union.