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 10–100s 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. Plain Language Summary: The pair of low altitude, polar AeroCube‐6 satellites observed stable small‐scale structure in the electrons present in low Earth orbit (LEO). Even when the two vehicles are separated in time by over a minute, both measure roughly the same structured time profile of radiation intensity, offset by the time separation between vehicles. Individual features in this stable structure are known as curtains. We test whether the curtains could be formed by accumulation of electrons from short‐lived microbursts of radiation intensity, which individually last less than a second. Accordingly, each microburst adds electrons to the population that reaches LEO but does not enter the atmosphere before drifting into the atmosphere in the South Atlantic Anomaly. Because microbursts contain many energies, over time the sub‐second temporal structure will spread out during the bounce and drift motion of the electrons. Further, if the microburst source repeatedly produces bursts in the same location, fluxes from new and old bursts will eventually overlap. Thus, it is possible that satellites in LEO with wide‐energy sensors to see a stable temporal profile reflective of the spatial structure of the microburst source locations. We demonstrate this hypothesized mechanism by tracing electrons in a dipole magnetic field. Key Points: Curtains are small‐scale latitude structures observed by a pair of low altitude satellitesWe use test particle tracing to investigate the origin of curtainsCurtains can be caused by microbursts, which are transient, smaller‐scale structures [ABSTRACT FROM AUTHOR]