Electric fields measured by ISEE‐1 within and near the neutral sheet during quiet and active times

A statistical survey of electric fields observed at 146 neutral sheet crossing events of the ISEE‐1 satellite during 1980 has been made. The observations can be divided into two classes — quiet or turbulent — according to the magnitude of the standard deviation in the 3 second spin period sine wave least‐squares fit to the electric field data. Events classified as turbulent are also turbulent in the magnetic field. During quiet crossings, the dawn‐dusk component of the electric field, E_y, is usually constant to ≲ 1/2 mV/m, with larger variations sometimes occurring over 2‐10 minute time scales. During turbulent crossings, E_y fluctuates rapidly with 3‐second‐average peak‐to‐peak amplitudes of 2‐16 mV/m, and instantaneous field magnitudes up to ∼ 30 mV/m. Turbulent crossings correlate with high levels of ground magnetic activity as indicated by AE and ground magnetograms, and with southward interplanetary magnetic field, while quiet crossings occur primarily during periods of low magnetic activity and northward or mixed interplanetary magnetic field.