Propagation of 3–10 MeV electrons in the inner heliosphere: Ulysses observations Original Research Article

Since the 1970ʹs electrons in the MeV energy range, of Jovian origin, have been extensively studied near the ecliptic from close to the Sun to beyond the Kronian orbit. The Ulysses trajectory provides a unique opportunity to study the propagation of several MeV electrons in a wide range of heliographic latitudes. From the Ulysses launch up to the end of 1992, the 3–10 MeV energy electron count rate of the COSPIN/KET instrument has been consistent with simple expectations from Jovian electron propagation. From the beginning of 1996 to the end of 1999, Ulysses was below 40 degrees heliographic latitude and between 4 and 5.4 AU from the Sun, making it the first spacecraft to reach the region around Jupiterʹs orbit with the planet being at the opposite side of the Sun. During this period, the electron flux has surprisingly increased and has stayed since then at the same level as in 1990 when Ulysses was magnetically well connected to Jupiter. In this paper, we present the corresponding data and discuss the possible origin of this electron flux as well as the implications for particle propagation in the three-dimensional heliospheric magnetic field.