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. Copyright 2005 by the American Geophysical Union.