Forward Modeling of the Type III Radio Burst Exciter

In this work, we propose a forward-modeling method to study the trajectory and speed of the interplanetary (IP) Type-III radio burst exciter. The model assumes that the source of an IP Type-III radio burst moves outward from the Sun following the Parker spiral field line. Using the arrival time of the radio waves at multiple spacecraft, we are able to determine the trajectory of the radio source in the Ecliptic plane, and its outward speed, as well as the injection time and longitude of the associated electron beam near the solar surface that triggers the Type-III radio burst. For the application of this method, we design a system to gather the arrival time of the radio wave from the radio dynamic spectra observed by Solar Terrestrial Relations Observatory (STEREO)/WAVES and Wind/WAVES. Then the system forward models the trajectory and speed of the radio burst exciter iteratively according to an evaluation function. Finally, we present a survey of four Type-III radio bursts that are well discussed in the literature. The modeled trajectories of the radio source are consistent with the previous radio-triangulation results, the longitude of the associated active region, or the location of Langmuir waves excited by the electron beam.