PARTICLE EVENTS ASSOCIATED WITH LOCAL TYPE-III RADIO-EMISSION AND LANGMUIR-WAVES IN THE INTERPLANETARY MEDIUM

The first detection of local type III radio emissions at the fundamental and harmonic of the plasma frequency was made by the Ulysses spacecraft when it was in the ecliptic plane and between similar to 1.4 and similar to 2.2 AU from the Sun. In-situ Langmuir waves were observed simultaneously with each local radio event, indicating the presence of an electron beam at the spacecraft. We analyze the energetic electron (42-290 keV) and ion (60-5000 keV) fluxes measur ed by the HI-SCALE instrument on Ulysses and examine the magnetic field and plasma structures present in the interplanetary medium during the times of the three reported local type III events. An impulsive electron event was found to be associated with each of the local radio events. For two events, the electron fluxes were observed simultaneously in all energy channels, indicating that an interplanetary structure, with propagating energetic particles already present, convected past the spacecraft. One of these structures is seen in association with a magnetic cloud. The presence of energetic electrons of solar origin reveals that one end of the structure field lines on which they move was still magnetically connected to the Sun. However, the back streaming electrons present a loss cone with high angles (50 degrees-60 degrees) which indicates that the other side of the magnetic field lines cannot be rooted back at the Sun and are essentially opened into the outer heliosphere. The last observation indicates that the structure is either a substructure of the magnetic cloud or at;he edge of the cloud. The local fundamental and 2nd harmonic radiation and in-situ Langmuir waves were observed as Ulysses entered the cloud. For the third local type III event a velocity dispersion in the onset times of the energetic electrons was observed. The measured velocity dispersion was used to determ ine the ejection time of the electrons at the Sun and to estimate the lowest energy (8 +/- 3 keV) of the electrons at the spacecraft at the onset of the local radio emission. The minimum energy of the electrons associated with the other local radio events was estimated to be similar to 6 +/- 1 and 24 +/- 3 keV. These estimated minimum electron energies, associated with the production of in-situ Langmuir waves, are consistent with previous direct measurements by sp acecraft at 1 AU.