The relationship between pulsating auroras observed from the ground and energetic electrons and plasma density measured at geosynchronous orbit

Abstract

We present comparisons of ground‐based all‐sky video recordings of pulsating auroral events and magnetically conjugate geosynchronous orbit measurements of high‐energy electrons and low‐energy plasma. The large‐scale pulsation events were found to be closely tied to substorm electron injections. For most events, only upper limits were available for the plasma density, which was ≤1–2 cm−3. We were unable to find any clear dependence between the plasma density and the pulsations. There were, however, small, rapid fluctuations in the density which had apparent spatial scales similar to those of individual pulsating auroral patches. These simultaneous measurements of the electron flux, plasma density, and pulsation period should be of use in constraining theoretical treatments of the pulsating aurora problem. We find that the conditions for minimum plasma density and plasma density gradient predicted by Demekhov and Trakhtengerts (1994) may not be supported by the geosynchronous data but that their prediction for minimum energetic electron density is supported. Predictions by Davidson and Chiu (1987) of the minimum change in plasma density and electron flux also seem to be supported. The data indicate that the principal factor controlling the onset of pulsations over a particular area may be the arrival of substorm‐injected electrons at the conjugate equator. This conclusion could provide the basis for a visible magnetic mapping of the substorm injection region through observations of the pulsating aurora.