Intense, variable electric fields at ionospheric altitudes in the high latitude regions as observed by DE‐2

Intense, variable electric fields have been observed by DE-2 using the double probe technique at ionospheric altitudes in high latitude regions. Measurements are made of both components of the electric field in the orbit plane (90 deg geographic inclination) at a rate of 16 samples/sec (0.5 km spatial resolution). Small scale, spike-like variations with amplitudes of over 100 mV/m are frequently seen in the polar cusp region and, to a lesser degree, also in the nightside auroral oval. Magnitudes up to 240 mV/m have been observed. These variations often occur over scale lengths of a few km or less. The fine structure in the cusp is consistent with the concept of limited regions of direct access within a larger overall region. It would appear that the intense electric fields which are observed at higher altitudes in the magnetosphere may penetrate to lower altitudes more extensively than indicated by previous measurements.