Electron Precipitation Curtains – Simulating the Microburst Origin Hypothesis

We explore the hypothesis that electron precipitation curtains such as those observed by the AeroCube-6 satellite pair can be produced by electron microbursts. Precipitation curtains are latitudinal structures of stable precipitation that persist for timescales of 10s of seconds or longer. The electrons involved have energies of 10s-100s of keV. The microburst formation hypothesis states that a source region in the equatorial region produces a series of very low frequency chorus wave emissions. Each of these emissions in turn produces a microburst of electron precipitation, filling the drift and bounce loss cone on the local field line. Electrons in the drift loss cone remain on the field line and bounce-phase mix over subsequent bounces while also drifting in azimuth. When observed at downstream azimuths by a satellite equipped with an integral energy sensor, no bounce phase structure remains, or, equivalently, the same time profile is present when two such satellites pass by many seconds apart. The spatial structure that remains reflects the pattern of microburst sources. Statistical studies of where and when curtains occur have indicated that some, but not all, curtains could be caused by microbursts. We use test particle tracing in a dipole magnetic field to show that spatially stationary source regions generating periodic microbursts can produce curtain signatures azimuthally downstream. We conclude that one viable explanation for many of the curtains observed by the AeroCube-6 pair is the accumulation of drift-dispersed microburst electron byproducts in the drift loss cone.