A new scenario for type III solar radio emission

This paper describes a new scenario for type III solar radio emission. Whil e the conventional theories emphasize Langmuir waves propagating along the ambient magnetic field, the present model stresses extraordinary-mode Berns tein waves with quasi-perpendicular wave vectors. The present model relies on plasma inhomogeneity and wave reflection to produce the electromagnetic radiation, in contrast to the conventional theories, which rely on nonlinea r wave-wave and wave-particle interactions. The essence of the model is tha t Bernstein waves with frequencies above the X-mode cutoff frequency are fi rst excited. Initially these waves can only propagate toward regions with h igher density and magnetic field. During this process, quasi-electrostatic Bernstein waves spontaneously convert to electromagnetic waves and rapidly reach the local X-mode cutoff frequency. Subsequently, these waves are refl ected and propagate away from the source region. The escaping radiation is observed as the type III emission. It is pointed out that in general, the o bserved radiation should possess one band in the dynamic spectrum. However, under certain conditions, the present theory is also capable of explaining the appearance of a pair of bands similar to those commonly called the "fu ndamental" and "harmonic" components in the literature. The present model r esolves some of the inconsistencies between the usual plasma emission hypot hesis and the observed pair emissions.