Observations of incoherent-scatter plasma-line intensities, measured i
n the E-region with the European Incoherent Scatter UHF radar, during
auroral precipitation, are presented. Intensities up to 200 times the
thermal level were observed in a restricted frequency interval from 5.
5 to 6.5 MHz. Intensities were lower at both higher and lower frequenc
ies. The intensities are compared with quantitative estimates based on
model suprathermal electron fluxes for the prevailing conditions. The
minimum in suprathermal electron fluxes between 2 and 4 eV, which is
caused by the excitation of vibrational levels in N-2, is found to res
ult in a minimum in expected plasma-line damping and a maximum in inte
nsity between 5.5 and 6.5 MHz, for the EISCAT UHF wavelength. Good agr
eement is found between the calculated and observed intensities.