Observations of large electric fields near the plasmasheet boundary by ISEE‐1

We report the first observations of large electric field spikes (up to ∼ 80 mV/m) at distances of 7 ‐ 23 R_E. Almost all of these spikes are detected within one minute of encountering the high latitude plasmasheet boundary, as identified by energetic particle detectors. These strong electric fields occur in regions of enhanced low frequency turbulence and in regions of field‐aligned current flow. Individual electric field spikes are well‐correlated with small‐scale gradients in particle fluxes and small‐scale currents. If these high altitude events are mappings of the low altitude electrostatic shocks, these data provide evidence that poleward auroral field lines map to the boundary of the plasmasheet.