Analysis and modeling of microburst precipitation

Observations from a recent rocket experiment that measured electrons over the energy range of 1-300 keV shows that microburst temporal structures exist from about 20 keV to > 120 keV. Simultaneous observations at five different pitch-angles (0 degrees-90 degrees) show the distribution is nearly isotropic during the bursts, while at low activity (quiet times and the valleys between microbursts) the distribution is anisotropic with higher fluxes at larger pitch-angles. The energy spectra were reasonably fit with a Maxwellian, with an e-folding energy E(0) approximate to 6-9 keV for alpha = 0 degrees, which increases to approximate to 10 keV at 67 degrees. A modeling of electron spectra using the theory of pitch-angle diffusion can reproduce the observed spectra, suggesting pitch-angle scattering of electrons due to a wave-particle interaction is the primary mechanism responsible for microbursts.