A survey of flux transfer events observed by Cluster during strongly northward IMF

Abstract

During Cluster's annual dayside seasons (November-June) the four spacecraft cross the magnetopause at high latitudes near local noon, and at lower latitudes further along the flanks. During these crossings, observations of flux transfer events (FTEs), a signature of transient or variable-rate magnetopause merging, are often made. We have compiled a survey of FTEs observed by Cluster in the 2002/3 dayside season. A significant number of FTEs, presented here, were observed under strongly northward IMF. Multi-spacecraft techniques enable more accurate velocities to be calculated than previously possible. The observed velocities are consistent with a long, component merging X-line emanating from the antiparallel merging site in the lobe, but require a relaxation of the antiparallel merging hypothesis to allow the X-line to extend to regions of lower shear on the flank. The velocities observed at lower latitudes are not consistent with a subsolar X-line.