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Propagation of EMIC Waves Inside the Plasmasphere: A Two‐Event Study
Author(s) -
Wang G.,
Zhang T. L.,
Gao Z. L.,
Wu M. Y.,
Wang G. Q.,
Schmid D.
Publication year - 2019
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2019ja027055
Subject(s) - plasmasphere , physics , computational physics , geophysics , wave propagation , poynting vector , magnetosphere , magnetic field , optics , quantum mechanics
Electromagnetic ion cyclotron (EMIC) waves are important for the loss of high‐energy electrons in the radiation belt. Based on the measurements of Van Allen Probes, two events during the same storm period are presented to study the propagation of EMIC waves. In the first event, left‐handed polarized EMIC waves were observed near the plasmapause, while right‐handed waves were observed in the inner plasmasphere. The Poynting flux of the right‐hand waves was mainly directed inward and equatorward, and no positive growth rates were obtained in the region of these right‐hand waves, indicating the inward propagation of the waves from a higher L ‐shell. In the second event, the wave vectors were quasi‐perpendicular to the background magnetic field inside the plasmaspheric plume but became quasi‐parallel outside. This phenomenon can be explained by the refraction of the large density gradient, which qualitatively satisfies Snell's law. These observations provide indirect evidence of the inward propagation of the EMIC waves and give a new insight on how density gradients may modify wave properties.