Precipitating electron energy spectra and auroral power estimation by
incoherent scatter radar with high temporal resolution
Abstract
This study presents an improved method to estimate differential energy
flux, auroral power and field-aligned current of electron precipitation
from incoherent scatter radar data. The method is based on a newly
developed data analysis technique that uses Bayesian filtering to fit
altitude profiles of electron density, electron temperature, and ion
temperature to observed incoherent scatter spectra with high time and
range resolutions. The electron energy spectra are inverted from the
electron density profiles. Previous high-time resolution fits have
relied on the raw electron density, which is calculated from the
backscattered power assuming that the ion and electron temperatures are
equal. The improved technique is applied to one auroral event measured
by the EISCAT UHF radar and it is demonstrated that the effect of
electron heating on electron energy spectra, auroral power and upward
field-aligned current can be significant at times. Using the fitted
electron densities instead of the raw ones may lead to wider electron
energy spectra and auroral power up to 75% larger. The largest
differences take place for precipitation that produces enhanced electron
heating in the upper E region, and in this study correspond to fluxes of
electrons with peak energies from 3 to 5 keV. Finally, the auroral power
estimates are verified by comparison to the 427.8 nm auroral emission
intensity, which show good correlation. The improved method makes it
possible to calculate unbiased estimates of electron energy spectra with
high time resolution and thereby to study rapidly varying aurora.