THE POLARIZATION OF 2ND-HARMONIC CORONAL TYPE-III BURSTS

The process of second harmonic plasma emission is considered, where tw o simplifying approximations made in previous treatments are relaxed. The revised theory can account for strong polarisation observed in som e harmonic coronal type III bursts, and predicts that a correlation be tween these bursts and the fastest electron beam speeds associated wit h type III emission should be apparent. These high observed degrees of polarisation could not be explained in the earlier theory. In most ca ses, polarisation in the sense of the magnetoionic o-mode is predicted . The predicted degree of polarisation is shown to be strongly depende nt on the form of the Langmuir wave number spectrum, and in particular on the magnitude of the wave number offset between beam-driven and ba ckscattered Langmuir waves.