Electron butterfly distribution modulation by magnetosonic waves. Issue 7 (14th April 2016)

• Record Type: Journal Article
• Authors: Maldonado, Armando A.; Chen, Lunjin; Claudepierre, Seth G.; Bortnik, Jacob; Thorne, Richard M.; Spence, Harlan
• Is Part Of: Geophysical research letters. Volume 43:Issue 7(2016)
• Page Start: 3051
• Page End: 3059
• Publication Date: 2016-04-14
• Subjects: Van Allen -- butterfly -- magnetosonic -- electron -- magnetosphere -- wave particle; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2016GL068161
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The butterfly pitch angle distribution is observed as a dip in an otherwise normal distribution of electrons centered about α eq =90°. During storm times, the formation of the butterfly distribution on the nightside magnetosphere has been attributed to L shell splitting combined with magnetopause shadowing and strong positive radial flux gradients. It has been shown that this distribution can be caused by combined chorus and magnetosonic wave scattering where the two waves work together but at different local times. Presented in our study is an event on 21 August 2013, using Van Allen Probe measurements, where a butterfly distribution formation is modulated by local magnetosonic coherent magnetosonic waves intensity. Transition from normal to butterfly distributions coincides with rising magnetosonic wave intensity while an opposite transition occurs when wave intensity diminishes. We propose that bounce resonance with waves is the underlying process responsible for such rapid modulation, which is confirmed by our test particle simulation. Key Points: Unlike Berstein‐mode waves, the observed waves are not bound by neighboring harmonics of the proton gyrofrequency Electron pitch angle distribution is modulated by the magnetosonic wave intensity Bounce resonance with magnetosonic waves is the mechanism behind our event's electron pitch angle distribution as shown by our simulation