Production of fine structures in type III solar radio bursts due to turbulent density profiles

Spacecraft measurements show that the plasma density in the solar wind and corona fluctuates with a frequency spectrum suggestive of Kolmogorov turbulence. Type III solar radio bursts are produced by energetic electron beams accelerated during solar flares. Spectral and/or temporal fine structures are commonly seen in type III bursts; in extreme cases the bursts can appear chain-like and are called type IIIb bursts. In this work we investigate the effects of density turbulence on type III bursts. We simulate the formation of coronal type III bursts in source regions with power-law density fluctuation spectra, and predict the radio emission observable at 1 AU. We find that turbulence leads to both temporal and spectral irregularities in the radio flux, due to variations in scattering path lengths, group speeds, and locations and sizes of emitting volumes at a given frequency. For instance, density depletions (increases) relative to the smooth background profile cause emission to arrive earlier (later) than expected. Moderate levels of density perturbations yield intensifications that tend to be broadband in fundamental emission but narrowband in the harmonic, possibly explaining type IIIb-III pairs as being cases where the harmonic intensifications are not resolved experimentally. Intensifications in harmonic emission may be resolvable if the turbulence levels are sufficiently large, producing type IIIb-IIIb pairs.