The changing topology of the duskside magnetopause boundary layer in relation to IMF orientation

Abstract

On 7 December 2000, Cluster made an extended outbound radial traversal of the duskside magnetopause boundary layer. The long duration of the crossing, during which Cluster spent several hours within 2RE of the nominal magnetopause, allows us to deconvolve the structure of this boundary layer in its dependence on interplanetary parameters. We present evidence that as the interplanetary magnetic field (IMF) changed in discontinuous jumps from southward to northward, the magnetic topology of the boundary layer evolved from open to closed. Reconnection signatures, including enhanced flows observed locally at Cluster and ion energy dispersion signatures observed by FAST near Cluster’s magnetic footpoint, appeared while the IMF was southward. When the IMF turned nearly due northward, Cluster observed 75-s (Pc 4) oscillations which we attribute to the Kelvin-Helmholtz instability.