Whistler mode chorus waves have recently been established as the most likely candidate for scattering relativistic electrons to produce the electron microbursts observed by low altitude satellites and balloons. These waves would have to propagate from the equatorial source region to significantly higher magnetic latitude in order to scatter electrons of these relativistic energies. This theoretically proposed propagation has never been directly observed. We present the first direct observations of the same discrete rising tone chorus elements propagating from a near equatorial (Van Allen Probes) to an off-equatorial (Arase) satellite. The chorus is observed first on the more equatorial satellite and is found to be more oblique and significantly attenuated at the off-equatorial satellite. This is consistent with the prevailing theory of chorus propagation and with the idea that chorus must propagate from the equatorial source region to higher latitudes. Ray tracing of chorus at the observed frequencies confirms that these elements could be generated parallel to the field at the equator, and propagate through the medium unducted to Van Allen Probes A and then to Arase with the observed time delay, and have the observed obliquity and intensity at each satellite.
Bibliographical noteFunding Information:
This work was supported by RBSP‐EFW funding provided by JHU/APL contract 922613, under NASA's prime contract NAS5‐01072, and by NASA grant 80NSSC19K0842. Research was supported by the International Space Science Institute's (ISSI) International Teams program. G.L.D. wishes to thank Pat Colestock for stimulating discussions. G.L.D. and G.S.C. were supported by the Laboratory Directed Research and Development program at Los Alamos National Laboratory (LANL) under project 20200073DR. LANL is operated by Triad National Security, LLC, for the National Nuclear Security Administration of U.S. Department of Energy (DOE) (Contract No. 89233218CNA000001). Y.M. is supported from JSPS KAKENHI (15H05815, 15H05747, 16H06286, and 20H01959). This study was supported by JSPS Bilateral Open Partnership Joint Research Projects and Grant‐in‐Aid for Scientific Research (20K14546) of Japan Society for the Promotion of Science (JSPS).
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- Radiation Belt
- Simultaneous observations