ISEE‐1 observations of electrostatic shocks on auroral zone field lines between 2.5 and 7 Earth radii

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Abstract
The ISEE‐1 satellite frequently passes through electrostatic shocks and the low altitude auroral particle acceleration region at geocentric radial distances less than ≈ 7 RE and as low as ≈ 2 RE. A sampling of data from the quasi‐static electric field experiment during 22 such passes revealed events (defined as regions of low frequency turbulence) containing electrostatic shocks (defined as an electric field ⩾ 100 mV/m) during 8 of the passes, which is an occurrence frequency comparable to that obtained near apogee on the S3‐3 satellite. Examination of three such electrostatic shocks shows that typical potentials of a few kV and latitudinal scale widths mapped to the ionosphere of a few km are encountered. From the latitudinal widths of the shocks and from the magnitudes of their observed electric fields, it is argued that the parallel electric field and auroral particle acceleration region may be confined to geocentric distances less than a few RE.