Institution(s): 1. Observatoire de Paris
During a flare, high energy electrons (1–100 keV) are expelled from the solar corona and travel along the interplanetary magnetic field lines. These electrons are at the origin of one of the most prominent features of the meter-decameter ranges of frequency: the so-called solar type III radio emissions.
Several theories have been proposed to explain the generation of these emissions. They all refer to small scale plasma processes. During this talk, we will show how STEREO/WAVES measurements have been able to give strong support to the model initially proposed by Ginzburg & Zheleznyakov: the three wave-coupling.
Using new capabilities of waveform analyses provided by the instruments onboard the two STEREO spacecraft, we present a complete set of direct evidence for three-wave coupling occurring during a Type III emission and involving two Langmuir waves and an ion acoustic wave. Evidence cover not only the energy and momentum conservation but also the phase coupling.
Then, we present Vlasov numerical simulations that support the observations. We indeed show that the amplitude of the wave packets are within the expected values when correctly considering the non monochromatic character of the waves and their finite interaction time.
Finally, during a specific event when two electron beams interact, we show that the lack of Langmuir waves coherence reduces the efficiency of the Langmuir parametric decay, and as a consequence reduces the intensity of the Type III emission.