Do Jovian electrons influence the terrestrial outer radiation zone?

Using energetic electron data (30 keV ‐ 2 MeV) from instruments onboard spacecraft 1976‐059A at synchronous orbit (6.6 R E ), we have been able to study relatively long‐term electron flux variations. Recurrently, and often with a 27‐day periodicity, the daily average 0.2‐2.0 MeV electron spectrum hardens dramatically. This change, wherein the power law spectral index goes from γ ∼ 3‐4 to γ ≲ 2, occurs during quiet geomagnetic (low K p ) periods usually several days after the leading edge of high‐speed solar wind streams have gone past the earth. The spectral hardening is seen to be produced by a large increase in the ≳ 1 MeV electron flux; by contrast, electrons with E < 1 MeV show flux increases several days earlier than the high‐energy component and this lower energy component is in close time synchronism with high solar wind speeds. Based on nearly 2.5 years of available data, it also appears that the high‐energy electron flux may undergo an ∼ 13‐month periodicity, and for many recurrent peak intensity events we see that the flux maximum at 6.6 R E occurs ∼2 days after Jovian electron intensities have peaked outside the magnetosphere at IMP 7/8. Thus we suggest the possibility that Jovian electrons might contribute significantly at times to the terrestrial electron radiation belt population.