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Influence of wave normal angles on hiss‐electron interaction in Earth's slot region
Author(s) -
Gao Yuzhu,
Xiao Fuliang,
Yan Qi,
Yang Chang,
Liu Si,
He Yihua,
Zhou Qinghua
Publication year - 2015
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2015ja021786
Subject(s) - hiss , physics , electron , pitch angle , van allen radiation belt , diffusion , atomic physics , momentum (technical analysis) , computational physics , nuclear physics , plasma , magnetosphere , geophysics , finance , economics , thermodynamics
Wave‐particle interaction which occurs in the radiation belts is generally determined by variations in wave normal angles. Using the Gaussian wave normal angle ( X = tan θ ) distribution, we study the influence of peak wave normal angle ( X m= tan θ m ) on gyroresonance between plasmaspheric hiss waves and energetic electrons in the slot regions L = 2.5, 3.0, and 3.5. The bounce‐averaged diffusion coefficients are calculated for different X m = 0,1,3,5, and then the phase space density (PSD) evolutions of energetic electrons driven by hiss waves are simulated over a continuous energy range 0.2–5 MeV. As X m increases, diffusion coefficients basically decrease mainly from the medium to a critical pitch angle α c for E k ≤1.0 MeV but increase at lower pitch angles for E k >1.0 MeV. Differences of diffusion coefficients between X m = 0 and 1 are close but become substantial as X m ≥3. Hiss can cause substantial drops in electron PSDs for E k ≤0.5 MeV and X m ≤1 from the loss cone α L to α c . For E k ≥1.0 MeV, such PSD drops become much smaller and confined in the lower pitch angles close to α L for each X m . In contrast, electron PSD increases for E k ≤1.0 MeV above α c at L = 2.5 and 3.0, probably because momentum diffusion coefficients increase steeply above α c . The current results demonstrate that gyroresonance between plasmaspheric hiss and energetic electrons in the slot region is strongly associated with variations of peak wave normal angles, which should be integrated into future global modeling of radiation belt dynamics.