Identification of foreshock waves with 3‐s periods

A new class of ULF waves present in the foreshock was discovered by Le et al. [1992] in the ISEE magnetometer data. These waves are observed in the upstream region only when the interplanetary magnetic field intersects the bow shock; they have periods near 3 s and are observed when the plasma β is high. They are always right‐hand nearly circularly polarized in the spacecraft frame and are convected downstream by the solar wind. We study the association of these waves with suprathermal ions and find that when the waves are in regions with a quiet magnetic field, they are accompanied by reflected ion beams. When the waves are observed in regions with a more irregular background field, the associated ions have more isotropic distributions. We study the kinetic instabilities that can be generated by the interaction of reflected beams with the solar wind. By comparing the properties (frequency, wavenumber, polarization, magnetic compression, and noncoplanar ratio) of the observed waves with the dispersion relation of linear kinetic instabilities we find that 3‐s waves can be identified as the right‐hand nonresonant instability, being right‐handed and propagating downstream in the plasma 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.