Rapid flattening of butterfly pitch angle distributions of radiation belt electrons by whistler‐mode chorus

• Published in: Geophysical research letters Vol. 43; no. 16; pp. 8339 - 8347
• Main Authors: Yang, Chang, Su, Zhenpeng, Xiao, Fuliang, Zheng, Huinan, Wang, Yuming, Wang, Shui, Spence, H. E., Reeves, G. D., Baker, D. N., Blake, J. B., Funsten, H. O.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.08.2016; American Geophysical Union
• Subjects: Angular distribution; ASTRONOMY AND ASTROPHYSICS; Butterflies; butterfly pitch-angle distribution; chorus waves; Dynamics; Evolution; Flattening; Jupiter; Lightning; Pitch angle; quasi-linear simulation; Radiation belt; Radiation belts; Simulation; Van Allen Probes; wave/particle interactions
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2016GL070194

Van Allen radiation belt electrons exhibit complex dynamics during geomagnetically active periods. Investigation of electron pitch angle distributions (PADs) can provide important information on the dominant physical mechanisms controlling radiation belt behaviors. Here we report a storm time radiation belt event where energetic electron PADs changed from butterfly distributions to normal or flattop distributions within several hours. Van Allen Probes observations showed that the flattening of butterfly PADs was closely related to the occurrence of whistler‐mode chorus waves. Two‐dimensional quasi‐linear STEERB simulations demonstrate that the observed chorus can resonantly accelerate the near‐equatorially trapped electrons and rapidly flatten the corresponding electron butterfly PADs. These results provide a new insight on how chorus waves affect the dynamic evolution of radiation belt electrons. Key Points Energetic electron angular distribution evolution during a geomagnetic storm Gyroresonant interaction between whistler‐mode chorus and energetic electrons Chorus acceleration can rapidly flatten the butterfly angular distribution