We consider a new mechanism for the generation of short-scale, &lgr;∥~10 cm, electron density fluctuations giving rise to plasma line enhancements measured by incoherent scatter radars in the auroral E region. It is explained as a coupling (conversion) of long-scale Langmuir waves generated by precipitated electron beams with short-scale ion-acoustic waves. The latter are supposed to be driven by field-aligned currents associated with the precipitation. This mechanism is most effective inside the thin layer of the enhanced plasma turbulence, named the plasma turbulence layer. ¿ American Geophysical Union 1994