Statistical nature of impulsive electric fields associated with fast ion flow in the near‐Earth plasma sheet

Statistical characteristics of impulsive electric field (IEFD) associated with fast earthward ion flows in the inner central plasma sheet were studied by using electric field data obtained from the double‐probe instrument on board the Geotail satellite. It is shown that the strongest electric field is produced in the region between X AGSM = −15 R E and −9 R E where the fast earthward flow is decelerated. The IEFDs are short‐lived with a timescale of ∼2 min on the average, compatible with the timescale of other signatures of substorm fine structures. This strong cross‐tail electric field, coincident with the braking of the fast flow and correlated with the magnetic field dipolarization, has important implications for the particle acceleration in the near‐Earth plasma sheet.