Enhanced ion acoustic fluctuations have been recently observed by incoherent scatter radars in the upper ionosphere. Here it is suggested that these fluctuations can be due to the Langmuir wave decay L→L'+S. In this process the ''pump'' Langmuir waves (L) are produced by a beam instability due to streaming soft electrons. Those waves then produce backscattered Langmuir waves (L') and ion acoustic waves (S). Estimations of the required electron beam energy and flux, as well as the beam number density are given. It is found that satellite and rocket observations support this interpretation. ¿ American Geophysical Union 1993