Auroral electron energies: comparisons of in situ measurements with spectroscopically inferred energies

Abstract

Auroral electron characteristic energies determined from ground-based photometer measurements of the ratio of 5577 Å OI and 4278 Å N₂⁺ emissions are compared with electron energies measured during two rocket flights into pulsating aurora. Electron spectra with Maxwellian energy distributions were observed in both flights with an increase in characteristic energy during each pulsation. During the first flight on February 15, 1980 values of E₀ ranging from 1.4 keV at pulsation minima to 1.8 keV at pulsation maxima were inferred from the 5577/4278 ratios, in good agreement with rocket measurements. During the second flight on February 23, 1980 direct electron energy measurements yielded E₀ values of 1.8 keV rising to 2.1 keV at pulsation maxima. The photometeric ratio measurements in this case gave inferred E₀ values about 0.5 keV lower. This apparent discrepancy is considered due to cloud cover which impaired the absolute emission intensity measurements. It is concluded that the 5577/4278 ratio does yield a meaningful measure of the characteristic energy of incoming electrons. This ratio technique when added to the more sensitive 6300/4278 ratio technique usable in stable auroras can now provide more complete monitoring of electron influx characteristics.