On 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 supercritical shock front and tend to evolve into a 'ring' in the downstream region behind the overshoot. This ring type ion distribution drives low frequency waves 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 assuming that the Dory-Guest-Harris distribution correctly describes the 'ring' nature of the reflected ions. It is proposed that frequency splitting in the observed radiation both at the frequency fundamental and at the second harmonic is due to the nonlinear scattering of electron-beam excited Langmuir and upper-hybrid waves parallel and perpendicular to the magnetic field by the ion-beam excited whistler and lower-hybrid waves, respectively, into left-handed circularly polarized electromagnetic waves. The frequency splitting is approximately equal to the electron cyclotron frequency.