A dynamical ionosphere is depicted using spectral analysis of the plasma line echo from the incoherent scatter radar at Sondrestrom, Greenland. F region plasma lines have been observed between 8.5 and 12 MHz, and E region plasma lines between 3 and 6 MHz. Accurate measurements of cutoff edges at the F layer peak and the E/F region valley have been made. Complexities in the plasma line spectra near the cutoff are related to microstructure within the radar interrogation volume. An observed asymmetry in the up- and downshifted cutoff frequencies may allow vertical electron velocity measurements and hence determination of field-aligned currents. Variations in the cutoffs over time and during moving-beam experiments have shown many passing disturbances, some of which are too small to detect using ion line returns. This technique can be applied to atmospheric gravity wave research and to the morphology of the complex high-latitude ionosphere. ¿ American Geophysical Union 1995