Observations by Ulysses of a pure electron event and its associated type III radio emission of 15 December 1990

We describe an interplanetary electron event associated with a type III radio burst observed by Ulysses at 1.37 AU. This event was observed when the spacecraft crossed a region of strong compression between a fast and a slow solar wind stream, characterized by a relatively high density and a complex behaviour of the plasma density, magnetic field and energetic electron anisotropy. The coronal source of the event is identified and the structure of the interaction region is discussed; in particular, it contains a stream interface and a relatively thin overdense region in which one component of the magnetic field varies rapidly and the energetic electrons temporarily loose their anisotropy