Estimates of the north-south electric field component in the magnetotail low latitude boundary layer

The measurements of O+ ions drift velocity in the magnetotail boundary layer are used to infer the North‐South Ez component of the local electric field. It is shown that Ez is generally a substantial component of the field and that it reverses its sign from the dawn to the dusk side of the northern magnetotail between XSM=−15 RE and XSM=−23 RE.