Large-scale simulations of solar type III radio bursts: flux density, drift rate, duration, and bandwidth

Abstract

Non-thermal electrons accelerated in the solar corona can produce intense coherent radio emission, known as solar type III radio bursts. This intense radio emission is often observed from hundreds of MHz in the corona down to the tens of kHz range in interplanetary space. It involves a chain of physical processes from the generation of Langmuir waves to nonlinear processes of wave-wave interaction. We develop a self-consistent model to calculate radio emission from a non-thermal electron population over large frequency range, including the effects of electron transport, Langmuir wave-electron interaction, the evolution of Langmuir waves due to non-linear wave-wave interactions, Langmuir wave conversion into electromagnetic emission, and finally escape of the electromagnetic waves. For the first time we simulate escaping radio emission over a broad frequency range from 500~MHz down to a few MHz and infer key properties of the radio emission observed: the onset (starting) frequency, {identification as fundamental or harmonic emission}, peak flux density, instantaneous frequency bandwidth, and timescales for rise and decay. Comparing with the observations, these large scale simulations enable us to identify the processes governing the key type III solar radio burst characteristics.