Nonrelativistic electron stream propagation in the solar atmosphere and solar wind: Type III bursts

Electron streams with type III burst characteristics are numerically modeled. The electron stream distribution is assumed to be one-dimensional in spatial and velocity space and the corresponding excited plasma wave spectrum is assumed to be one-dimensional in spatial and phase velocity space. The quasilinear equations with the addition of spontaneous emission, magnetic and collisional effects are numerically solved as an initial value problem with time, space, and velocity as the independent variables for a solar-type background plasma and a type-III-like stream. Background density and temperature spatial structure, spontaneous emission, magnetic fields, electron-ion collisions, stream wave reabsorption and wave pileup are shown to affect stream propagation and are incorporated into a physical description of this propagation. The calculated electron flux time profiles at the earth suggest scatter-free propagation and compare well with type III stream observations. If fundamental and second harmonic radiation is assumed to be proportional to the plasma wave energy density and to the square of the plasma wave energy density, respectively, the calculated wave energy density profiles compare very well with simple, singly peaked type III burst radio profiles for all frequencies considered. The calculated spectra suggest that either or both fundamental and second harmonic emission could create the observed radio spectra for frequencies above a few MHz. Conversely, the calculated burst durations, burst excitation times, and burst exponential decay times all suggest that observed radiation at low frequencies is second harmonic