Signatures of electron Landau resonant interactions with chorus waves from THEMIS observations
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Simultaneous observations of electron phase space density (PSD) and chorus waves for more than 4 years by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) are analyzed to identify signatures of the electron Landau resonant interactions with chorus waves in the radiation belts. Chorus waves play an important role in the radiation belt dynamics by effectively interacting with electrons. Landau resonant interactions arise when the waves are not exactly parallel propagating. Such interactions lead to "plateaus" along v(II) in the electron velocity distributions, where v(II) is the parallel (with respect to the background magnetic field) component of the electron velocity. The analyzed electron PSDs often demonstrate local minima in the derivative of the velocity distribution along v(II) near the Landau resonant velocity calculated from the simultaneous in situ wave observations. These minima are, therefore, direct signatures and solid evidence of the electron Landau resonant interactions with chorus waves.