Abstract
One of the most interesting topics in space physics is the interaction of the solar wind with the Earth's magnetosphere. This interaction involves various waves, in particular upstream of the bow shock. Among these upstream waves, we study some of them, which are generated by back-streaming particles coming from the shock ramp. They are observed in the ion foreshock region, and they are electromagnetic large-amplitude compressional Ultra Low Frequency (ULF) electromagnetic waves. There are four different types of ULF waves in the ion foreshock: Sinusoidal, Shocklets, Discrete wave packets, and three second waves. In this paper, we focus on the upstream 3-s waves, via an analysis of their magnetic components. We use a minimum variance analysis, for which we construct a computer program, which calculate the eigenvalues (strength), the eigenvectors (direction), and the rotation of the components of the wave magnetic field. We apply this program on a set of filtered data from ISEE 2 satellite of upstream 3-s waves taken on Nov., 1979. We check that the eigenvalues are all real and positive values. For both the global interval and in shorter intervals containing highly oscillated wave packets, these waves are observed to be circularly polarized with well defined wave vectors (in minimum variance direction u3). They have quasi-parallel propagation, although the angle between (u3, B) is not exactly zero. Their central frequencies slightly vary with time.