Energy spectral characteristics of auroral electron microburst precipitation

Abstract

Abstract.We consider data from a rocket experiment designed to study auroral microburst precipitation. Our rocket instruments had high energy spectral resolution which allowed us to characterize the electron energy spectra. Data from the field aligned electron detector show that the majority of the spectra fit an exponential form in the 45-70 keV energy range. Approximately 15% of the spectra fit a power law form for high energies (70-150 keV) and 45% fit an additional exponential form for low energies (20-45 keV).The multi-component spectra appeared during both microburst and non-burst times. The e-folding energies for the 45-70 keV energy range increased as the flux increased. Some of these features can be explained by a cyclotron wave-particle interaction mechanism. We also observed a weak peak in the energy spectrum at about 45 keV, suggesting the existence of field-aligned potential drops associated with microburst production.

Review of radiation belt relativistic electron losses

“…Subsequent balloon experiments up to $300 keV showed that microbursts are the primary form of electron precipitation observed on the dayside and thus represent a major loss mechanism (Parks, 1978). High resolution measurements of microbursts up to 150 keV were made from a rocket, and the majority of event spectra fit an exponential with e-folding between 40 and 75 keV (Reinard et al, 1997). However, 4400 keV precipitation with rapid temporal variations was also observed and related to microbursts (Blake et al, 1966).…”

Anisotropic pitch angle distribution of ~100 keV microburst electrons in the loss cone: measurements from STSAT-1

“…Microburst precipitation has been observed since the early sixties by balloon-borne X-ray experiments in the energy range of ∼20-100 keV (Anderson and Milton, 1964). Microbursts can be characterized by exponential energy spectra with e-folding energies E 0 ∼ 5-20 keV (Anderson et al, 1966;Lampton, 1967;Rosenberg et al, 1990;Reinard et al, 1997;Datta et al, 1997). To distinguish them from the relativistic microbursts, we call these low energy microbursts.…”

Short-duration Electron Precipitation Studied by Test Particle Simulation

“…7) has a fast-rising and slow-falling shape, while the STSAT-1 observations generally show slow-rising and fast-falling microburst structures. Various types and shapes of microbursts have been observed; Datta et al (1997) showed that the different shapes of these microbursts could correlate to variations of the diffusion coefficient. The diffusion rate depends on the wave amplitude in the wave-particle interaction process, implying that microburst shapes are determined by whistlermode wave structures.…”

“…However, electrons at 100 keV interact with waves in the torial region where the loss cone has a small angle, and electrons can be scattered into the loss cone. may explain why microbursts are not detected at 10 keV, while 100 keV electron microbursts have been rved (Datta et al 1997;Lee et al 2005). Electrons with energies in the MeV range can interact with waves at high latitudes, where the loss cone e is larger.…”

“…They were discovered by X-ray balloon-borne experiments in the early sixties (Anderson & Milton 1964). Microbursts in the 20-100 keV energy range can be characterized by exponential energy spectra with e-folding energies E 0~5 -20 keV (Anderson et al 1966;Rosenberg et al 1990;Reinard et al 1997).…”