Simultaneous measurements of X-rays and electrons during a pulsating aurora

N Østgaard,K Aarsnes,J Stadsnes,M Smith,K Måseide,J Sharber,F Søraas

doi:10.1007/s005850050588

Abstract

The PULSAUR II rocket was launched from AndÃ¸ya Rocket Range at 23.43 UT on 9 February 1994 into a pulsating aurora. In this paper we focus on the observations of precipitating electrons and auroral X-rays. By using models it is possible to deduce the electron energy spectrum from X-ray measurements. Comparisons are made between the deduced electron fluxes and the directly measured electron fluxes on the rocket. We found the shape of the observed and the deduced electron spectra to fit very well, with almost identical e-folding energies in the energy range from 10 ke V to ~60â80 ke V. For the integrated fluxes from 10.8 to 250 ke V, we found a discrepancy of 30% . By combining two models, we have found a good method of deducing the electron precipitation from X-ray measurements. The discrepancies between calculations and measurements are in the range of the uncertainties in the measurements.Key words. Ionospheric particle precipitation Â· Magnetospheric physics Â· Annual phenomena Â· Energetic particle

Highlights

Pulsaur II was a sounding rocket aimed at the study of generating mechanisms of pulsating aurora and related ionospheric eects
As the models are based upon the assumption of isotropic electron precipitation in the downward hemisphere, we have eliminated this source of discrepancy by calculating an equivalent isotropic distribution, i.e. the isotropic distribution that results in the same energy deposition in the atmosphere as the anisotropic distribution
Similar comparisons between precipitating energetic electrons and X-rays have been performed by others

Summary

Introduction

Pulsaur II was a sounding rocket aimed at the study of generating mechanisms of pulsating aurora and related ionospheric eects. As the models are based upon the assumption of isotropic electron precipitation in the downward hemisphere, we have eliminated this source of discrepancy by calculating an equivalent isotropic distribution, i.e. the isotropic distribution that results in the same energy deposition in the atmosphere as the anisotropic distribution In this calculation we have taken into account the backscattering of the electrons as a function of dierent pitch angles assuming that the 20-keV electrons can represent the whole distribution. $ 50 keV we estimate an e-folding energy of $ 10 keV, above $ 90 keV we estimate an e-folding energy of several hundred of keV's and in the intermediate energy range we estimate $ 30 keV As this hard tail is observed every second early in theight, the spectrum shown in Fig. 12 strongly indicates that the electron spectra above 20 keV cannot be represented by only one exponential, but maybe by two exponentials or a dierent function, corresponding much better with the electron spectra we deduce from the X-ray spectra. There are some uncertainties in the determination of the lower energy threshold for the integral electron (HEED) detector

Discussion and conclusions

Findings

1.27 Very good agreement