Cluster/rapid energetic electron observations at the dayside magnetospheric boundary Original Research Article

We study the energetic electrons by the Cluster-II Rapid instrument on a dayside high-latitude pass on the night between March 21/22, 2001. The Cluster satellites were flying outward in the pre-noon sector, passing a cusp/cleft type region roughly at midnight. Contrary to earlier observations of high fluxes of energetic particles in the high-latitude cusp, we found a very low flux of energetic particles in this region. Soon thereafter the satellites entered the closed field line region of high-altitude magnetosphere with high fluxes of energetic particles and a low plasma density. While still in the region of downward oriented field lines, satellites observed surface waves propagating along magnetopause (MP) and modulating strongly the energetic particle fluxes. In the dayside sector satellites, observed several MP crossings, as well as periods when MP was quite stable and close to the satellites, even between them. We derive the speed and direction of the moving dayside magnetopause using observations of energetic electrons and plasma density. We also note that the moving magnetopause was often found to be connected with an increase of energetic electron flux while the stagnant MP was effectively a sink to energetic particles.