The transmission of upstream waves to the magnetosphere: An analysis at widely separated ground stations

On 18 February 2003 a long‐duration, almost monochromatic, wave event was detected by Cluster at radial distances from the bow shock smaller than ≈10 Re. The interplanetary magnetic field orientation determined a wide and almost symmetric foreshock region around the bow shock nose, providing highly favorable conditions for a direct wave penetration into the magnetosphere. The general correspondence between the characteristics of the wave trains observed in the foreshock region and at two widely separated ground stations (namely, at low latitudes in the Northern Hemisphere and in Antarctica) confirms that the ground activity is ubiquitously determined and controlled by the upstream activity. At low latitudes, the direct propagation of the external waves through the subsolar point is sharply confined to the dayside hemisphere. In Antarctica, the wave activity is detected even on field lines stretched into the tail; here the polarization pattern suggests a significant contribution of sunward propagating waves in the postmidnight hours, consistent with a wave penetration through the magnetotail lobes. At both stations the wave energy is typically ≈5–10% of the external energy; in addition, in Antarctica the contribution of the cusp turbulence largely overcomes that one related to the penetration of the upstream waves. Key Points The ground wave activity is ubiquitously controlled by the upstream activity At low latitudes the wave propagation is confined to the dayside hemisphere In Antarctica the polarization suggests sunward propagation in the morning