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M/Q = 2 ion distribution in the inner magnetosphere estimated from ion cyclotron whistler waves observed by the Akebono satellite
Author(s) -
Matsuda Shoya,
Kasahara Yoshiya,
Goto Yoshitaka
Publication year - 2015
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2014ja020972
Subject(s) - whistler , cyclotron , plasmasphere , magnetosphere , ion , physics , atomic physics , ionosphere , population , plasma , geophysics , nuclear physics , demography , quantum mechanics , sociology
In this study, we examine the spatial occurrence distributions of H + , He + , and M / Q = 2 ion band ion cyclotron whistler waves observed by the Akebono satellite below an altitude of 10,500 km. These ion cyclotron whistler waves are categorized as electromagnetic ion cyclotron mode waves with characteristic spectrum properties that depend on the ion composition in the plasma. Statistical research is particularly important for clarifying the variation of ion composition in a plasmaspheric ion environment. In this study, essential differences are noted among the observed regions of each ion cyclotron whistler wave band. Our statistical analysis showed that the generation of H + band ion cyclotron whistlers in the equatorial region is difficult, while M / Q = 2 ion band ion cyclotron whistlers are frequently observed near this region. Thus, a certain amount of M / Q = 2 ions is evident. To explain these statistical results, we propose a model for generation of several bands of ion cyclotron whistlers along a propagation path. In addition, we examine the magnetic local time dependence of the observed ion cyclotron whistlers. The spatial occurrence distribution of the M / Q = 2 ion cyclotron whistler waves is greatest inward of L ∼ 2.4 in the local dayside; however, they extend to L ∼ 3.0 in the local nightside. Our results suggest a density enhancement process of M / Q = 2 ions in the nightside plasmasphere, which is consistent with previous satellite observations. Thus, this study presents important knowledge on the effects of minor ion population on wave propagation and generation.