Rapid outward extension of electron radiation belt driven by substorm injection and chorus waves

Tuesday, 16 December 2014
Zhenpeng Su1, Hui Zhu1, Fuliang Xiao2, Huinan Zheng1, Yuming Wang1, Zhaoguo He3, C Shen4, Min Zhang1, Shui Wang1, Craig Kletzing5, William S Kurth5, George B Hospodarsky6, Harlan E. Spence7, Geoffrey D Reeves8, Herbert O Funsten9, J Bernard Blake10 and Daniel N. Baker11, (1)University of Science and Technology of China, Hefei, China, (2)Changsha University of Science and Technology, Changsha, China, (3)Organization Not Listed, Washington, DC, United States, (4)Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing, China, (5)University of Iowa, Physics and Astronomy, Iowa City, IA, United States, (6)Univ Iowa, Iowa City, IA, United States, (7)University of New Hampshire Main Campus, Durham, NH, United States, (8)Los Alamos National Laboratory, Los Alamos, NM, United States, (9)Los Alamos Natl Laboratory, Los Alamos, NM, United States, (10)The Aerospace Corp, Los Angeles, CA, United States, (11)University of Colorado, Laboratory for Atmospheric and Space Physics, Boulder, CO, United States
The electron radiation belts undergo drastic changes on a variety of timescales ranging from minutes to decades. Here we concentrate on the rapid evolution of outer electron radiation belt on a timescale of hours observed by RBSP and THEMIS satellites on 26 May 2013. The outer boundary of the electron radiation belt moved from L=5.5 to L>6.07 during about 6 hours. Near the outer boundary (L=6.0), the 30keV-5MeV electron fluxes increased by up to four orders of magnitude. We propose a two-step scenario involving substorm injection and the subsequent chorus-driven acceleration to explain this rapid extension event. The substorm injection alone can cause 100% and 20% of the total subrelativistic (<0.2MeV) and relativistic (2-5MeV) electron flux enhancements within a few minutes. Such injection process was sequentially recorded by the two radially displaced RBSP satellites. The subsequent stochastic acceleration by chorus waves can yield 60%-80% of the total energetic (0.2-5.0MeV) electron flux enhancement within about 6 hours. The strong chorus waves were simultaneously detected by the RBSP and THEMIS satellites, and such local acceleration process is supported by the data-driven STEERB simulations. The current results clearly illustrate the respective importance of substorm injection and chorus waves for the evolution of radiation belt electrons at different energies on a relatively short timescale.