The case of the noisy derivatives—Evidence for a spacecraft‐plasma interaction

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Abstract
Data from the retarding potential analyzers on Atmosphere Explorers C and D indicate the existence of 2‐m irregularities in the ion flux to the satellite. These irregularities are seen only occasionally, and usually very near the magnetic dip equator. They occur both in sunlight and eclipse and span at least two decades of ion concentration. They tend to be present when the spacecraft is moving nearly parallel to B and are not seen at all from the low latitude AE‐E orbit. We believe the irregularities, whose amplitude is of the order of 1% of the background ion flux, are the result of a spacecraft interaction with the ionospheric plasma. A mechanism for producing this interaction that utilities a fast beam of ambient ions reflected upstream from the satellite to produce a two‐stream instability is examined in some detail.