This study investigates the energy spectrum of electron microbursts observed by the Focused Investigations of Relativistic Electron Burst Intensity, Range, and Dynamics II (FIREBIRD-II, henceforth FIREBIRD) CubeSats. FIREBIRD is a pair of CubeSats, launched in January 2015 into a low Earth orbit, that focus on studying electron microbursts. High resolution electron data from FIREBIRD-II consists of 5 differential energy channels between 200 keV and 1 MeV and a $>$1 MeV integral channel. This covers an energy range that has not been well studied from low Earth orbit with good energy and time resolution. This study aims to improve understanding of the scattering mechanism behind electron microbursts by investigating their spectral properties and their relationship to the equatorial electron population under different geomagnetic conditions. Microbursts are identified in the region of the North Atlantic where FIREBIRD only observes electrons in the bounce loss cone. The electron flux and exponential energy spectrum of each microburst is calculated using a FIREBIRD instrument response modeled in GEANT4 (GEometry ANd Tracking) and compared with the near equatorial electron spectra measured by the Van Allen Probes. Microbursts occurring when the AE index is enhanced tend to carry more electrons with relatively higher energies. The microburst scattering mechanism is more efficient at scattering electrons with lower energies, however the difference in scattering efficiency between low and high energy is reduced during periods of enhanced AE.

Microbursts are impulsive (<1s) injections of electrons (few keV to >MeV) from the outer radiation belt into the atmosphere, primarily caused by nonlinear scattering by chorus waves. Although attempts have been made to quantify their contribution to outer belt electron loss, the uncertainty in the overall size and duration of the microburst region is typically large, so that their contribution to outer belt loss is uncertain. We combine datasets that measure chorus waves (Van Allen Probes (RBSP), Arase, ground-based VLF stations) and microburst (>30 keV) precipitation (FIREBIRD II and AC6 CubeSats, POES/MetOp) to determine the size of the microburst-producing chorus source region beginning on 5 December 2017. We show that the lower/upper limits on the long-lasting (~30 hours) microburst precipitation region is 4 to 8 MLT and 2 to 8.5 L. We conclude that microbursts likely represent a major loss source of outer radiation belt electrons for this event.

Microbursts are an impulsive increase of electrons from the radiation belts into the atmosphere and have been directly observed in low Earth orbit and the upper atmosphere. Prior work has estimated that microbursts are capable of rapidly depleting the radiation belt electrons on the order of a day, hence their role to radiation belt electron losses must be considered. Losses due to microbursts are not well constrained, and more work is necessary to accurately quantify their contribution as a loss process. To address this question we present a statistical study of > 35 keV microburst sizes using the pair of AeroCube-6 CubeSats. The microburst size distribution in low Earth orbit and the magnetic equator was derived using both spacecraft. In low Earth orbit, the majority of microbursts were observed while the AeroCube-6 separation was less than a few tens of km, mostly in latitude. To account for the statistical effects of random microburst locations and sizes, Monte Carlo and analytic models were developed to test hypothesized microburst size distributions. A family of microburst size distributions were tested and a Markov Chain Monte Carlo sampler was used to estimate the optimal distribution of model parameters. Finally, a majority of observed microbursts map to sizes less then 200 km at the magnetic equator. Since microbursts are widely believed to be generated by scattering of radiation belt electrons by whistler mode waves, the observed microburst size distribution was compared to whistler mode chorus size distributions derived in prior literature.

Curtain precipitation are a recently discovered stationary, persistent, and latitudinally narrow electron precipitation phenomenon in low Earth orbit. Curtains are observed over consecutive passes of the dual AeroCube-6 CubeSats while their in-track lag varied from a fraction of a second to 65 seconds, with dosimeters that are sensitive to > 30 keV electrons. This study uses the AeroCube-6 mission to quantify the statistical properties of 1,634 curtains observed over three years. We found that many curtains are narrower than 10 kilometers in the latitudinal direction with 90\% narrower than 20 kilometers, corresponding to a few hundred kilometer radial size at the magnetic equator. We examined the magnetic local time and geomagnetic dependence of curtains. We found that curtains are observed in the late-morning and pre-midnight magnetic local times, with a higher occurrence rate at pre-midnight, and curtains are observed more often during times of enhanced Auroral Electrojet. We found a few curtains in the bounce loss cone region above the north Atlantic, whose electrons were continuously scattered for at least 6 seconds. Such observations suggest that continuous curtain precipitation may be a significant loss of > 30 keV electrons from the magnetosphere into the atmosphere, possibly scattered by a parallel direct current electric field.