Generation of downshifted oscillations in the electron foreshock: A loss‐cone instability

Abstract

Measurements performed aboard Cluster spacecraft near Earth's bow shock on 24 January 2001 provide convincing evidence of a loss‐cone feature within the electron foreshock region. This feature is formed by suprathermal electrons with energies 15–45 eV and pitch angles 130°–150° and is always accompanied by electrostatic waves with frequencies well below the local plasma frequency. An instability analysis shows that these downshifted oscillations can result from a loss‐cone instability of electron cyclotron modes rather than from the beam instability as previously suggested.