Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm53a1359c&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SM53A-1359
Physics
[2752] Magnetospheric Physics / Mhd Waves And Instabilities, [2753] Magnetospheric Physics / Numerical Modeling, [2772] Magnetospheric Physics / Plasma Waves And Instabilities, [2784] Magnetospheric Physics / Solar Wind/Magnetosphere Interactions
Scientific paper
More than 50 years ago, Dungy suggested that the Earth’s magnetosphere could support magnetohydrodynamic (MHD) resonances. Extensive observational and theoretical work has established the existence of resonant standing waves on closed geomagnetic field lines. These oscillations, known as field line resonances (FLR’s), are observed across most of the dayside magnetosphere and occupy the lowest frequency range of the ultra-low frequency (ULF) spectrum ( ≤ 100 mHz). The spatial distribution and polarization characteristics of toroidal mode FLR’s suggest that the solar wind is the ultimate source of the compressional energy that excites these resonances. However, it remains unclear which solar wind parameter(s) is responsible, with observational evidence supporting a Kelvin-Helmholtz mechanism and/or periodic fluctuations in the solar wind dynamic pressure. To investigate these issues, we present results from Lyon-Fedder-Mobarry (LFM) global MHD simulations of the solar wind-magnetosphere interaction. The simulations are driven by synthetic solar wind conditions, where idealized ULF oscillations are embedded in the upstream solar wind. The simulation results suggest that ULF oscillations in the solar wind dynamic pressure can drive toroidal mode FLR’s across most of the dayside magnetosphere. In addition, the simulation results suggest that these same upstream fluctuations can energize magnetospheric cavity mode oscillations. We find that the cavity mode oscillation and the FLR are coupled, which leads to an enhancement of the FLR’s at the cavity mode eigenfrequencies. Furthermore, we find no evidence that magnetopause Kelvin-Helmholtz (KH) waves, which are also present in our simulations, drive FLR’s. Finally, we show that the spatial and spectral characteristics of the dynamic pressure driven waves are more favorable for a radial diffusion-type interaction with radiation belt electrons, when compared with those of the KH waves.
Claudepierre Seth G.
Denton Richard E.
Hudson Mary K.
Lotko William
Lyon John
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