Electron Precipitation Curtains - Simulating the Microburst Origin
Hypothesis
- Thomas Paul O'Brien,
- Colby Lemon,
- J Bernard Blake
Abstract
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.