Radio dynamic spectra observed on 12 November 2010. (a) Triangular stria substructures observed along with regular type III radio bursts by all three spacecraft (STEREO A & B, and Wind) at about 08:10 UT. (b) Schematic representation of the outlines of the triangular stria substructures as observed by STEREO B and overlaid on STEREO A and Wind observations. the spectrum also shows other regular type III radio bursts during the same time period.