Radio dynamic spectra observed on 19 September 2011 shows a group of type III bursts. (a) Type III bursts with stria substructures were observed along with regular type III radio bursts. Emission was strongest in observations by STEREO B. (b) Schematic representation of the outlines of the stria structures as observed by STEREO B and overlaid on STEREO A and Wind observations. The black frames in the right panel represents the same frequency range of 3000–200 KHz.