A Model of the Generation Mechanism of Type II Solar Radio Bursts

Abstract

The proposed model for the generation mechanism of type II solar radio bursts is based on the fact that a small fraction of ions is reflected from the shock front and tend to evolve into a 'ring' in the downstream region behind the overshoot. This ring type ion distribution drive low frequency waves (Omega i < w < Omega e) unstable which effectively accelerate the magnetized electrons of the ambient plasma to very high energies along the field lines since their phase velocities parallel to magnetic fields are much higher than the electron thermal velocity in the solar corona. The distribution function of the accelerated electrons is calculated in the present paper assuming that Dory-Guest-Harris distribution correctly describes the 'ring' nature of the reflected ions. It is proposed that the frequency splitting in the observed radiation both at fundamental and at second harmonic is due to the non-linear scattering of electron-beam excited Langmuir and upper-hybrid waves parallel and perpendicular to the magnetic field on the ion-beam-excited whistler and lower-hybrid waves respectively into left-handed circularly polarized electromagnetic waves. The frequency splitting is approximately equal to electron cyclotron frequency.