Solitary Waves Observed By Cluster In the Solar Wind.

Short dropouts of the magnetic field intensity have been frequently observed in the solar wind on interplanetary spacecraft. But so far it could not be established whether these are caused by kinetic instabilities or whether they can be described as solitary MHD waves. The multi-satellite observations of the Cluster-mission allow for the first time to measure proton and electron distributions with a sufficient temporal and spatial resolution to tackle this question. We use measurements by the FGM magnetometer, the CIS ion spectrometer, the PEACE electron instrument and the Whisper plasma wave instrument to investigate the role of protons, heavy ions and electrons for the stability of the structures. We also use the 4-satellite observations of the Cluster magnetic field instrument to determine the proper motion of these structures relative to the solar wind. The presence of foreshock waves close to the Earth bowshock strongly limits the event selection. In the current paper we discuss a 10 s linear wave without sufficient particle data resolution and a 4 min wave for which particle distributions are available. The larger wave shows that the stability of the structure might be caused by changes in the thermal electron distributions while proton and α distributions are unaffected. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]