Alfvén waves in the foreshock propagating upstream in the plasma rest frame: Statistics from CLUSTER observations., Ann

Part of Special Issue “Spatio-temporal analysis and multipoint measurements in space” Abstract. We statistically study various properties of low-frequency waves such as frequencies, wave numbers, phase velocities, and polarization in the plasma rest frame in the ter-restrial foreshock. Using Cluster observations the wave tele-scope or k-filtering is applied to investigate wave numbers and rest frame frequencies. We find that most of the fore-shock waves propagate upstream along the magnetic field at phase velocity close to the Alfvén velocity. We identify that frequencies are around 0.1×cp and wave numbers are around 0.1×cp/VA, where cp is the proton cyclotron fre-quency and VA is the Alfvén velocity. Our results confirm the conclusions drawn from ISEE observations and strongly support the existence of Alfvén waves in the foreshock. Key words. Electromagnetics (wave propagation) – Inter-planetary physics (planetary bow shocks) – Space plasma physics (waves and instabilities)