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Wiley, Journal of Geophysical Research. Space Physics, 10(119), p. 8262-8273

DOI: 10.1002/2014ja020023

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Interactions of energetic electrons with ULF waves triggered by interplanetary shock: Van Allen Probes observations in the magnetotail

This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

We present in situ observations of a shock-induced substorm-like event on April 13, 2013 observed by the newly launched Van Allen twin probes. Substorm-like electron injections with energy of 30 ~ 500 keV were observed in the region from L ~ 5.2 to 5.5 immediately after the shock arrival (followed by energetic electron drift echoes). Meanwhile, the electron flux was clearly and strongly varying on the ULF wave time scale. It is found that both toroidal and poloidal mode ULF waves with a period of 150 s emerged following the magnetotail magnetic field reconfiguration after the IP shock passage. The poloidal mode is more intense than the toroidal mode. The 90° phase shift between the poloidal mode Br and Ea suggests the standing poloidal waves in the northern hemisphere. Furthermore, the energetic electron flux modulations indicate that the azimuthal wave number is ~14. Direct evidence of drift resonance between the injected electrons and the excited poloidal ULF wave has been obtained. The resonant energy is estimated to be between 150 keV and 230 keV.Two possible scenaria on ULF wave triggering are discussed: vortex-like flow structure driven FLR and ULF waves growth through drift resonance. It is found that the IP shock may trigger intense ULF wave and energetic electron behaviour at L ~ 3 to 6 on the nightside, while the time profile of the wave is different from dayside cases.