Premium
Generation of He + and O + EMIC waves by the bunch distribution of O + ions associated with fast magnetosonic shocks in the magnetosphere
Author(s) -
Lee K. H.,
Lee L. C.
Publication year - 2016
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 - 10.1002/2016gl070465
Subject(s) - magnetosphere , physics , cyclotron , emic and etic , ion , atomic physics , computational physics , van allen probes , plasma , nuclear physics , van allen radiation belt , quantum mechanics , sociology , anthropology
Electromagnetic ion cyclotron (EMIC) waves are often observed in the magnetosphere with frequency usually in the H + and He + cyclotron bands and sometimes in the O + band. The temperature anisotropy, caused by injection of energetic ions or by compression of magnetosphere, can efficiently generate H + EMIC waves, but not as efficient for He + or O + EMIC waves. Here we propose a new generation mechanism for He + and O + EMIC waves associated with weak fast magnetosonic shocks, which are observed in the magnetosphere. These shocks can be associated with either dynamic pressure enhancement or shocks in the solar wind and can lead to the formation of a “bunch” distribution in the perpendicular velocity plane of O + ions. The O + bunch distribution can excite strong He + EMIC waves and weak O + and H + waves. The dominant He + EMIC waves are strong in quasi‐perpendicular propagation and show harmonics in frequency spectrum of Fourier analysis. The proposed mechanism can explain the generation and some observed properties of He + and O + EMIC waves in the magnetosphere.