The propagation of ULF waves from the Earth's foreshock region to ground: The case study of 15 February 2009

Abstract

A long-duration upstream ultralow frequency (ULF) wave event was detected on 15 February 2009 by Cluster satellites, close to the bow shock nose. A clear wave activity was identified when the interplanetary magnetic field orientation was favorable to the local generation. We examined the wave properties in both the solar wind and the spacecraft frame during a selected time interval and found that foreshock waves were ssentially Alfven waves propagating at a small angle with respect to the interplanetary magnetic field. A comparison of Cluster observations with those on the ground, in the polar cap and at low-latitude stations, confirms the results of previous studies, indicating that upstream waves can reach different ground regions along different paths.