Evidence of scattering effects on the sizes of interplanetary Type III radio bursts

An analysis is conducted of 162 interplanetary Type III radio bursts; some of these bursts have been observed in association with fast electrons and Langmuir wave events at 1 AU and, in addition, have been subjected to in situ plasma parameter measurements. It is noted that the sizes of burst sources are anomalously large, compared to what one would anticipate on the basis of the interplanetary plasma density distribution, and that the variation of source size with frequency, when compared with the plasma frequency variation measured in situ, implies that the source sizes expand with decreasing frequency to fill a cone whose apex is at the sun. It is also found that some local phenomenon near the earth controls the apparent size of low frequency Type III sources.