A strong high-frequency radio wave incident on the ionosphere is capable of exciting enhanced electron plasma waves via a parametric wave-plasma coupling interaction. Incoherent backscatter radar is used to obtain detailed power spectra of these enhanced plasma waves. Power and frequency asymmetries are detected between spectra of enhanced plasma waves propagating parallel and antiparallel to the radar line-of-sight at the altitude of observation. The power spectra are corrected for the antenna gain frequency dependence. The power asymmetry is attributed to linear convective amplification of the plasma waves, so that waves observed propagating parallel and antiparallel to the radar line-of-sight have originated at different altitudes, above and below the observation height. The frequency asymmetry is interpreted as a Doppler shift of the power spectra resulting from a downward static drift of the thermal electrons. This drift is necessary to maintain charge neutrality within the wave-plasma interaction region, replacing upward-escaping energetic electrons which have been bootstrap accelerated by the enhanced plasma waves.