Evidence of Naturally Occurring Wave-Wave Interactions in the Polar Ionosphere and its Relation to Naturally Enhanced Ion Acoustic Lines

In this paper we present the first observational evidence of naturally occurring wave-wave interactions in the polar ionosphere, using data obtained with the EISCAT Svalbard Radar (ESR). The simultaneous and co-located observations of enhancements in the ion and plasma lines can only be explained in terms of wave-wave interactions taking place within the scattering volume. These measurements strengthen previous indications that Langmuir wave decay/turbulence triggered by a low energy electron beam associated with the aurora may be the source of Naturally Enhanced Ion Acoustic Lines (NEIAL) observed with incoherent scatter radars over the last decade. Our main objectives and results in this paper are: (1) To show that our measurements represent experimental proof that wave-wave interactions take place in the ionosphere naturally. (2) To investigate the possibility that this wave-wave interaction is causally related to the NEIAL.