Coronal electron stream and langmuir wave detection inside a propagation channel at 4.3 AU

Abstract

Observations of an energetic interplanetary electron event associated with the production of Langmuir waves, both of which are identified at 4.3 AU by instruments on the Ulysses spacecraft, are presented in this paper. This electron event propagates inside a well‐defined magnetic structure. The existence of this structure is firmly established by joint particle and plasma observations made by Ulysses instruments. Its local estimated radial width is of the order of 2.3 × 107 km (0.15 AU). The electron beam is associated with a type III burst observed from Earth at high frequencies and at low frequencies from Ulysses in association with Langmuir waves detected inside the structure. The consistency of local (Ulysses) and remote (Earth) observations in terms of temporal and geometrical considerations establishes that the structure is anchored in the solar corona near the solar active region responsible for the observed type III emission and gives an accurate determination of the injection time for the observed electron beam. The width on the solar surface of the structure is estimated to be 6000 km. Propagation analysis of the electron event is presented. It is shown that this event is nearly scatter‐free. Ion plasma velocity variations inside the structure were very small in amplitude as well as in direction. The magnetic field inside this structure was also very quiet and organized. In order to quantify the magnetic field properties, a variance analysis has been performed and is presented in this paper. The analysis establishes that inside the structure the amount of magnetic energy involved in the fluctuations is less than 4% of the total magnetic energy; the minimal variance direction is well defined and in coincidence with the direction of the mean magnetic field. This configuration may produce conditions favorable for scatter free streaming of energetic electrons and/or Langmuir wave production. The results presented show that the magnetic field might play a role in stabilizing the coronal‐origin plasma structures and then preserving them to large, ∼ 4 AU, distances in the heliosphere.