Observational Evidence for the Parametric Decay in a Solar Type III Radio Burst

Abstract

The STEREO spacecraft has provided new observational evidence for the parametric interaction, known as the electrostatic decay instability in the source region of a solar type III radio burst. The in situ high time resolution wave observations show that Langmuir waves often occur as intense one dimensional magnetic field aligned beat type of wave packets, with spectra containing peaks at fpe , fpe − fS and fS , corresponding to the beam excited Langmuir waves (L), and respectively to the daughter Langmuir (L′) and ion sound S waves generated as a result of the electrostatic decay instability (ESD) L → L′ + S. Most probably, the beat pattern is due to beating between L and oppositely directed L′, and the beat frequency corresponds to ion sound frequency. The implication of these observations for theories of solar type III radio bursts is discussed.