Detection of langmuir solitons: implications for type III burst emission mechanisms at 2ω _PE

Abstract

We present the experimental verification of existing theoretical models of emission mechanisms of solar type III bursts at the second harmonic of the plasma frequency, ω_pe. This study is based on the detection of Langmuir and envelope solitons by the Ulysses spacecraft inside three type III burst source regions. We show that the oscillating-two-stream instability, coherent radiation by Langmuir solitons and stochastic phase mixing of the Langmuir waves in the strong turbulence regime are the appropriate emission mechanisms at 2ω_pe.