Identification of foreshock waves with 3-s periods

A new class of ULF waves present in the foreshock was discovered by Le et a l. [1992] in the ISEE magnetometer data. These waves are observed in the up stream region only when the interplanetary magnetic held intersects the bow shock; they have periods near 3 s and are observed when the plasma beta is high. They are always right-hand nearly circularly polarized in the spacec raft frame and are convected downstream by the solar wind. We study the ass ociation of these waves with suprathermal ions and find that when the waves are in regions with a quiet magnetic field, they are accompanied by reflec ted ion beams. When the waves are observed in regions with a more irregular background held, the associated ions have more isotropic distributions. We study the kinetic instabilities that can be generated by the interaction o f reflected beams with the solar wind. By comparing the properties (frequen cy, wavenumber, polarization, magnetic compression, and noncoplanar ratio) of the observed waves with the dispersion relation of linear kinetic instab ilities we find that 3-s waves can be identified as the right-hand nonreson ant instability, being right-handed and propagating downstream in the plasm a frame. We conclude that the waves associated with reflected/intermediate ions can be generated locally in the regions where they are observed, while the waves associated with diffuse distributions may be generated upstream from where they are observed.