Anatomy of a flux transfer event seen by Cluster

Abstract

Data from Cluster are used to study the structure of a flux transfer event (FTE), seen near the northern cusp. We employ Grad-Shafranov reconstruction, using measured fields from all four spacecraft to produce a map of the FTE cross section. The FTE consists of a flux rope of approximate size 1R_E and irregular shape, embedded in the magnetopause. Its axis $\hat{\bf{z} is tangential to the magnetopause. Since no reconnection signatures are seen, the map provides a fossil record of the prior reconnection process that created the flux rope: the strong core field indicates that it was generated by component merging. An average reconnection electric field >=0.18 mV/m must have occurred in the burst of reconnection that created the FTE. The total axial ($\hat{\bf{z}) current and magnetic flux in the FTE were -0.66 MAmp and +2.07 MWeber, respectively.