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 w ith 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 fas t earthward flow is decelerated. The IEFDs are short-lived with a timescale of similar to 2 min on the average, compatible with the timescale of other signatures of substorm fine structures. This strong cross-tail electric fi eld, coincident with the braking of the fast flow and correlated with the m agnetic field dipolarization, has important implications for the particle a cceleration in the near-Earth plasma sheet.