ULF Waves at Mercury
Authors: Eun-Hwa Kim, Scott A. Boardsen, Jay R. Johnson, and James A. Slavin
Abstract: Ultra-low frequency (ULF) waves are regularly observed at Mercury. A recent statistical study showed that the magnetic compressional component is dominant near the magnetic equator and the magnetic transverse component is dominant in the higher magnetic latitude. In this paper, we address possible interpretations of those waves. Because the observed waves typically exhibit linear polarization, they have been considered to be the field-line resonance (FLR) structure. When compressional waves propagate into the inner magnetosphere, they can mode convert to field-aligned waves associated with the ion-ion hybrid resonance. These transverse mode converted waves oscillate globally reaching high magnetic latitude. Alternatively, the electromagnetic ion Bernstein wave (IBW) has been considered as another possibility because of the strong power of the compressional component. Ray-tracing calculations of the IBW modes propagating in a dipole magnetic field suggest that electromagnetic IBWs are highly unstable to the proton loss cone distribution function with field-aligned group velocity. As the waves propagate they become highly compressional even in a moderate proton β plasma. Therefore, the compressional waves near the magnetic equator could be explained by the IBWs while transverse waves could be explained by the FLR concept.
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Submitted to: American Geophysical Union Geophysical Monograph Series 1/9/2015
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Download PPPL-5105 (pdf 2.3 MB 41pp)
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