Statistical Survey of Type III Radio Bursts at Long Wavelengths Observed by the Solar TErrestrial RElations Observatory (STEREO)/Waves Instruments: Goniopolarimetric Properties and Radio Source Locations

摘要

We have performed statistical analysis of a large number of Type III radiobursts observed by STEREO between May 2007 and February 2013. Only intense,simple, and isolated cases have been included in our data set. We have focusedon the goniopolarimetric (GP, also referred to as direction-finding) propertiesat frequencies between $125$ kHz and $2$ MHz. The apparent source size $\gamma$is very extended ($\approx60^\circ$) for the lowest analyzed frequencies.Observed apparent source sizes $\gamma$ expand linearly with a radial distancefrom the Sun at frequencies below $1$ MHz. We have shown that Type III radiobursts statistically propagate in the ecliptic plane. Calculated positions ofradio sources suggest that scattering of the primary beam pattern plays animportant role in the propagation of Type III radio bursts in the IP medium.