Standing Alfven waves transitioned from fast growing, travelling waves: Indications from electron measurements
Thursday, 4 September 2014: 9:40 AM
Regency Ballroom (Hyatt Regency)
Xuzhi Zhou1, Zi-Han Wang2, Qiugang Zong2, Seth G Claudepierre3, Margaret Kivelson4 and Vassilis Angelopoulos5, (1)University of California Los Angeles, Los Angeles, CA, United States, (2)Peking University, Beijing, China, (3)The Aerospace Corporation, Santa Monica, CA, United States, (4)UCLA, Los Angeles, CA, United States, (5)UCLA---ESS/IGPP, Los Angeles, CA, United States
Abstract:
Ultra-Low Frequency (ULF) electromagnetic oscillations, usually interpreted as standing Alfven waves, are one of the major candidates to explain the electron acceleration to relativistic energies in the Earth's radiation belt. Prompt acceleration can be achieved when electrons resonantly gain energy from the ULF waves (via a process named drift resonance), which is observationally characterized by an energy dependence of the phase differences between electron flux and electromagnetic field oscillations. Such dependence, recently observed by the Van Allen Probes, has been presented as a most unambiguous evidence for the drift-resonance acceleration (Claudepierre et al., 2013). In this paper, we revisit the same event to find that in the early stage of the waves, the observed phase relationship appeared to be not fully consistent with the drift resonance theory. We further examine these apparent inconsistencies, to suggest that they arose from the fast growth of travelling Alfven waves before being transitioned into the more typical standing waves. These observations, therefore, provide a rare opportunity to understand the generation and evolution of ULF oscillations in the Earth's magnetosphere.
