Observations of traveling Pc5 waves and their relation to the magnetic cloud event of January 1997

Measurements of ULF waves in the Pc5 frequency range are presented and disc ussed. The waves were observed during the magnetic cloud event of January 1 997 by instruments on the Polar satellite and ground instrumentation. These large-amplitude waves are best interpreted as traveling shear Alfven waves rather than in the usual standing-wave scenario. Characterization of the a ssociated complex particle environment shows that the waves were largely co nfined to the plasma trough. Energetic protons modulated by the wave are sh own to have caused modulated proton aurora. It is argued that the waves wer e caused by the interaction of a magnetic hole with the magnetosphere.