The Arecibo observatory and the powerful HF source at Islote when supplemented by portable HF and ULF receivers comprise a major natural laboratory for studying the midlatitude ionosphere. This grant is to study the effects observed when the ionosphere over Arecibo is irradiated with two strong HF signals. By measuring simultaneously the amplitudes of these waves, the contribution of the beat - frequency wave on sideband production will be assessed. Further studies will be undertaken which will examine the propagation characteristics of the launched ULF wave. The proposed experiments will aid in understanding the roles of the relevant nonlinear processes. *** //
