Simultaneous observations of energetic electrons and dawnside chorus in geosynchronous orbit

We present the first simultaneous observations of chorus activity and energetic particles from near‐geosynchronous orbit by using data from the Aerospace Corporation VLF receiver and the UCSD charged particle detector on the SCATHA satellite. We find that, for the 5 days studied, June 23–27, 1979, every encounter with injected clouds of energetic electrons was accompanied by chorus activity. We conclude that dawnside chorus is generated by substorm‐injected, anisotropic clouds of electrons with energies between 10 and 100 keV.