A case study of magnetotail current sheet disruption and diversion

On 1 Jun 1985 the AMPTE/CCE spacecraft (at a geocentric distance of ∼8.8 R E at the midnight neutral sheet region) observed a dispersionless energetic particle injection and an increase in magnetic field magnitude, which are features commonly attributed to disruption of the near‐earth cross‐tail current sheet during substorm expansion onsets. An analysis based on high time‐resolution measurements from the magnetometer and the energetic particle detector indicates that the current sheet disruption region exhibited localized (< 1 R E ) and transient (< 1 min) particle intensity enhancements, accompanied by complex magnetic field changes with occasional development of a southward magnetic field component. Similar features are seen in other current disruption/diversion events observed by the CCE. Our analysis suggests that the current disruption region is quite turbulent, similar to laboratory experiments on current sheet disruption, with signatures unlike those expected from an X‐type neutral line configuration. No clear indication of periodicity in any magnetic field parameter is discernible for this current disruption event.