DOI: 10.1002/2017JA025018
Scopus记录号: 2-s2.0-85041080327
论文题名: The Broadband Excitation of 3-D Alfvén Resonances in a MHD Waveguide
作者: Elsden T. ; Wright A.N.
刊名: Journal of Geophysical Research: Space Physics
ISSN: 21699380
出版年: 2018
卷: 123, 期: 1 起始页码: 530
结束页码: 547
语种: 英语
英文关键词: Alfven resonance
; Earth's magnetosphere
; field line resonance
; MHD waves
; mode coupling
英文摘要: This paper considers the resonant coupling of fast and Alfvén magnetohydrodynamic (MHD) waves. We perform numerical simulations of the time-dependent excitation of Alfvén resonances in a dipole magnetic field, with nonuniform density providing a 3-D equilibrium. Wright and Elsden (2016) showed that in such a system where the poloidal and toroidal Alfvén eigenfrequencies are different, the resonance can have an intermediate polarization, between poloidal and toroidal. We extend this work by driving the system with a broadband rather than monochromatic source. Further, we investigate the effect of azimuthal inhomogeneity on the resonance path. It is found that when exposed to a broadband driver, the dominant frequencies are the fast waveguide eigenfrequencies, which act as the drivers of Alfvén resonances. We demonstrate how resonances can still form efficiently with significant amplitudes, even when forced by the medium to have a far from toroidal polarization. Indeed, larger-amplitude resonances can be generated with an intermediate polarization, rather than purely toroidal, as a result of larger gradients in the magnetic pressure formed by the azimuthal inhomogeneity. Importantly, the resonance structure is shown to be independent of the different forms of driving, meaning their locations and orientations may be used to infer properties of the equilibrium. However, the amplitude of the FLRs are sensitive to the spatial structure and frequency spectrum of the magnetopause driving. These results have implications for the structure of field line resonances (FLRs) in Earth's magnetosphere, although the focus of this paper is on the underlying physics involved. ©2018. American Geophysical Union. All Rights Reserved. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/114722
Appears in Collections: 气候减缓与适应
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作者单位: Department of Mathematics and Statistics, University of St Andrews, St Andrews, United Kingdom
Recommended Citation:
Elsden T.,Wright A.N.. The Broadband Excitation of 3-D Alfvén Resonances in a MHD Waveguide[J]. Journal of Geophysical Research: Space Physics,2018-01-01,123(1)