Generation of lower and upper bands of electrostatic electron cyclotron harmonic waves in the Van Allen radiation belts

Zhou, Qinghua

Generation of lower and upper bands of electrostatic electron cyclotron harmonic waves in the Van Allen radiation belts

Tuesday, 11 July 2017

Furong Room (Cynn Hotel)

Qinghua Zhou¹, Fuliang Xiao¹, Chang Yang¹, Si Liu¹, Yihua He¹, Daniel N. Baker², Harlan E. Spence³, Geoffrey D Reeves⁴ and Herbert O Funsten⁴, (1)Changsha University of Science and Technology, Changsha, China, (2)University of Colorado at Boulder, Boulder, CO, United States, (3)University of New Hampshire Main Campus, Space Science Center, Durham, NH, United States, (4)Los Alamos National Laboratory, Los Alamos, NM, United States

Abstract:

Electrostatic electron cyclotron harmonic (ECH) waves generated by the electron loss cone distribution can produce efficient scattering loss of plasma sheet electrons, which has a significant effect on the dynamics in the outer magnetosphere. Here we report two ECH emission events around the same location L ≈ 5.7-5.8, MLT ≈ 12 form Van Allen Probes on 11 February (event A) and 9 January 2014 (event B), respectively. The spectrum of ECH waves was centered at the lower half of the harmonic bands during event A, but the upper half during event B. The observed electron phase space density (PSD) in both events is fitted by the subtracted bi-Maxwellian distribution, and the fitting functions are used to evaluate the local growth rates of ECH waves based on a linear theory for homogeneous plasmas. ECH waves are excited by the loss cone instability of 50 eV - 1 keV electrons in the lower half of harmonic bands in the low-density plasmasphere in event A, and 1 - 10 keV electrons in the upper half of harmonic bands in a relatively high density region in event B. The current results successfully explain observations and provide a first direct evidence on how ECH waves are generated in the lower and upper half of harmonic frequency bands.