Cluster observations of fast magnetosonic waves in the heliosphere current sheet

We present Cluster spacecraft observations of large-amplitude (δ|B|/|B|∼1) fast-mode magnetosonic waves in the heliospheric current sheet (HCS). The crossings of the HCS and the associated heliospheric plasma sheet (HPS) are encountered by Cluster in the near-Earth solar wind and by ACE upstream of Earth. Multiple current layers are detected in correspondence with small-scale discontinuities in the regime of open magnetic field lines within the HCS. Fast magnetosonic waves are observed at one current layer, accompanying the phase-steeped edge of a large-amplitude transverse Alfvén wave. The observed fast-mode waves are in the frequency range 0.01 Hz-0.2 Hz, characterized by a strong correlation between variations of plasma density and magnetic field strength. Analysis of ratio δE/δBindicate that the fast-mode wave packet consists of an antisunward propagating component and a larger sunward propagating component in the rest frame of the solar wind. The fast-mode waves are not observed by ACE in the upstream solar wind. The generation of the fast-mode waves may relate to the development of the phase-steeped Alfvén wave and has profound effects on the evolution of the solar wind plasma. Key Points Fast-mode waves at the steeped edge of large-amplitude Alfvén waves Direct measurements of current layers in correspondence with discontinuities Implications on the evolution of large-amplitude Alfvén waves in the solar wind