Author/Authors :
C. Mazelle، نويسنده , , C. and Meziane، نويسنده , , K. and LeQuéau، نويسنده , , D. and Wilber، نويسنده , , M. and Eastwood، نويسنده , , J.P. and Rème، نويسنده , , H. and Sauvaud، نويسنده , , J.A. and Bosqued، نويسنده , , J.M. and Dandouras، نويسنده , , I. and McCarthy، نويسنده , , M. and Kistler، نويسنده , , L.M. and Klecker، نويسنده , , B. and Korth، نويسنده , , A. and Bavassano-Cattaneo، نويسنده , , M.B. and Pallocchia، نويسنده , , G. and Lundin، نويسنده , , R. and Balogh، نويسنده , , A.، نويسنده ,
Abstract :
We present observations of E<40 keV/e backstreaming ions measured by the Cluster Ion Spectrometry experiment at 1–2RE upstream of the bow shock. The ions are simultaneously observed at all three spacecrafts for which CIS measurements are available. The proton distributions are analyzed using 4 s time resolution. They are observed in association with low-frequency quasi-monochromatic waves with substantial amplitudes (δB/B∼1). When the waves are present the ion distributions appear as gyrophase-bunched gyrating distributions while field-aligned beams are also observed just adjacent to the interval of wave occurrence. The gyrating distributions are observed at distances larger than an ion Larmor radius and they have pitch-angles inconsistent with a specular reflection mechanism at the bow shock. The properties of the ULF waves reveal that they are in cyclotron resonance with the ion parallel beams that could drive a right-hand ion/ion instability responsible for the wave occurrence. Moreover, the observed pitch-angles for the gyrating ion distributions are consistent with the theoretical value expected if they are produced by a coherent nonlinear wave–particle interaction.
