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Geophys Res Lett. 2019 Jun 16;46(11):5707-5716. doi: 10.1029/2019GL082152. Epub 2019 Jun 11.

EMIC Waves in the Outer Magnetosphere: Observations of an Off-Equator Source Region.

Author information

The Johns Hopkins University Applied Physics Laboratory Laurel MD USA.
Department of Physics Augsburg University Minneapolis MN USA.
Southwest Research Institute San Antonio TX USA.
Department of Physics and Astronomy University of Texas at San Antonio San Antonio TX USA.
Department of Earth, Planetary, and Space Sciences University of California Los Angeles CA USA.
Institute for Geophysics and Planetary Physics University of California Los Angeles CA USA.
Laboratory for Atmospheric and Space Physics University of Colorado at Boulder Boulder CO USA.
Department of Space and Plasma Physics Royal Institute of Technology Stockholm Sweden.
Space Science Center University of New Hampshire Durham NH USA.


Electromagnetic ion cyclotron (EMIC) waves at large L shells were observed away from the magnetic equator by the Magnetospheric MultiScale (MMS) mission nearly continuously for over four hours on 28 October 2015. During this event, the wave Poynting vector direction systematically changed from parallel to the magnetic field (toward the equator), to bidirectional, to antiparallel (away from the equator). These changes coincide with the shift in the location of the minimum in the magnetic field in the southern hemisphere from poleward to equatorward of MMS. The local plasma conditions measured with the EMIC waves also suggest that the outer magnetospheric region sampled during this event was generally unstable to EMIC wave growth. Together, these observations indicate that the bidirectionally propagating wave packets were not a result of reflection at high latitudes but that MMS passed through an off-equator EMIC wave source region associated with the local minimum in the magnetic field.

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