Pitch angle “Boomerang” evolution of relativistic electrons: ULF wave modulation

Hao, Yixin

Pitch angle “Boomerang” evolution of relativistic electrons: ULF wave modulation

Tuesday, 11 July 2017: 14:20

Furong Room (Cynn Hotel)

Yixin Hao¹, Qiugang Zong¹, Xuzhi Zhou¹, Robert Rankin², Xingran Chen¹, Ying Liu¹, Suiyan Fu¹, Harlan E. Spence³, J Bernard Blake⁴, Geoffrey D Reeves⁵ and Geoffrey D Reeves⁵, (1)Peking University, School of Earth and Space Sciences, Beijing, China, (2)University of Alberta, Physics, Edmonton, AB, Canada, (3)University of New Hampshire Main Campus, Space Science Center, Durham, NH, United States, (4)Aerospace Corporation Santa Monica, Santa Monica, CA, United States, (5)Los Alamos National Laboratory, Los Alamos, NM, United States

Abstract:

Pc5 band “boomerang-shaped” modulations on pitch angle distribution of relativistic electrons were observed in the outer radiation belt after a shock passage on 7 June 2014. Peaks and valleys in flux modulations of electrons with pitch angle closer to 90° arrive earlier. For 90° electrons, phase shift across energy channels exceeds 180° and the stripes in energy spectrogram tilt increasingly in following cycles. The azimuthal wave number of the poloidal ULF wave is estimated to be around 6 or 7 according to particle data. Pitch angle and energy dispersions unpredicted by conventional drift resonance studies indicate local time dependent ULF wave activities. The general agree- ment between observations and arrival time estimations validates the scenario that shock-induced ULF waves with a finite local time extent interact with electrons through drift resonance at the region westward from spacecraft. Numerical calculations with such modified ULF wave field reproduce the observed boomerang stripes and modulations in energy spectrogram with good consistence. Our study on boomerang stripes provides solid evidence of the localized drift-resonant interactions, adding new understanding to the outer belt dynamics.