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The Effects of Hydrogen Band EMIC Waves on Ring Current H + Ions
Author(s) -
Wang Zhiqiang,
Zhai Hao,
Gao Zhuxiu
Publication year - 2017
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2017gl075843
Subject(s) - ring current , physics , ion , atomic physics , phase (matter) , cyclotron , adiabatic process , hydrogen , magnetosphere , plasma , nuclear physics , quantum mechanics , thermodynamics
Hydrogen band electromagnetic ion cyclotron (EMIC) waves have received much attention recently because they are found to frequently span larger spatial areas than the other band EMIC waves. Using test particle simulations, we study the nonlinear effects of hydrogen band EMIC waves on ring current H + ions. A dimensionless parameter R is used to characterize the competition between wave‐induced and adiabatic motions. The results indicate that there are three regimes of wave‐particle interactions for typical 35 keV H + ions at L = 5: diffusive (quasi‐linear) behavior when α eq ≤ 35° ( R ≥ 2.45), the nonlinear phase trapping when 35° < α eq < 50° (0.75 < R < 2.45), and both the nonlinear phase bunching and phase trapping when α eq ≥ 50° ( R ≤ 0.75). The phase trapping can transport H + ions toward large pitch angle, while the phase bunching has the opposite effect. The phase‐trapped H + ions can be significantly accelerated (from 35 keV to over 500 keV) in about 4 min and thus contribute to the formation of high energy components of ring current ions. The results suggest that the effect of hydrogen band EMIC waves is not ignorable in the nonlinear acceleration and resonance scattering of ring current H + ions.