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EMIC waves covering wide L shells: MMS and Van Allen Probes observations
Author(s) -
Yu Xiongdong,
Yuan Zhigang,
Huang Shiyong,
Wang Dedong,
Li Haimeng,
Qiao Zheng,
Yao Fei
Publication year - 2017
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2017ja023982
Subject(s) - van allen probes , physics , emic and etic , magnetosphere , ring current , plasmasphere , computational physics , van allen radiation belt , geophysics , cyclotron , solar wind , astrophysics , ion , plasma , nuclear physics , quantum mechanics , sociology , anthropology
During 04:45:00–08:15:00 UT on 13 September in 2015, a case of Electromagnetic ion cyclotron (EMIC) waves covering wide L shells ( L = 3.6–9.4), observed by the Magnotospheric Multiscale 1 (MMS1) are reported. During the same time interval, EMIC waves observed by Van Allen Probes A (VAP‐A) only occurred just outside the plasmapause. As the Van Allen Probes moved outside into a more tenuous plasma region, no intense waves were observed. Combined observations of MMS1 and VAP‐A suggest that in the terrestrial magnetosphere, an appropriately dense background plasma would make contributions to the growth of EMIC waves in lower L shells, while the ion anisotropy, driven by magnetospheric compression, might play an important role in the excitation of EMIC waves in higher L shells. These EMIC waves are observed over wide L shells after three continuous magnetic storms, which suggests that these waves might obtain their free energy from those energetic ions injected during storm times. These EMIC waves should be included in radiation belt modeling, especially during continuous magnetic storms. Moreover, two‐band structures separated in frequencies by local He 2+ gyrofrequencies were observed in large L shells ( L > ~6), implying sufficiently rich solar wind origin He 2+ likely in the outer ring current. It is suggested that multiband‐structured EMIC waves can be used to trace the coupling between solar wind and the magnetosphere.