Oblique lower band chorus waves: Time shifts between discrete elements observed by the Cluster spacecraft (Art. No. A00F02)
Abstract
We report observations of remarkable frequency differences and time shifts between the corresponding elements of lower band chorus recorded by the four Cluster spacecraft at low magnetic latitudes in the source region on 20 January 2004. Surprisingly, the spacecraft located closer to the equator systematically received the corresponding chorus elements later than the spacecraft located at higher magnetic latitudes.
The time shifts and frequency differences depended almost linearly on the perpendicular distance between the various spacecraft. Analysis of data from both the wideband data and STAFF instruments shows that chorus emissions were generated with highly oblique angles of propagation.
We show that the sources moving across the magnetic field lines are reasonably consistent with these observations.