Statistics – Computation
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sm61a04l&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SM61A-04
Statistics
Computation
2736 Magnetosphere/Ionosphere Interactions, 2752 Mhd Waves And Instabilities, 7827 Kinetic And Mhd Theory, 7859 Transport Processes
Scientific paper
The transport of energy into the magnetosphere produced by a quasi-monochromatic boundary oscillation is considered. The study is based on results from a computational model for ultra-low-frequency magnetohydrodynamics in boundary-constrained geomagnetic flux coordinates that simulates a 160-sec, m=3 azimuthal and fieldline fundamental mode. New insights into the energy transport include: (1) A diagnostic for energy transport shows that earthbound energy flux accompaning poloidal/compressional propagation at higher L-values is diverted from the flux surface normal (radial-like) direction into the azimuthal direction at the fieldline resonant flux surface, and subsequently turns field-aligned where the signal becomes shear Alfvénic near azimuthal nodes in the compressional mode structure. (2) This behavior is a consequence of the azimuthal phase quadrature between the compressional cavity mode and the shear Alfvén resonance and may explain, in part, why the azimuthal group velocity of some dawn- and dusk-side ground observations of high-latitude field line resonances [Fenrich et al., 1995] exhibit a confusing statistical pattern, with both antisunward and sunward group propagation being common. (3) Evanescent decay of compressional signals and cavity modes generated by magnetopause fluctuations is counteracted, and can even be reversed at plasmapause altitudes and lower, by geometrical focusing of the earthbound compressional wave energy. The effect occurs for low m numbers (<6 for numerical parameters of this study) and may explain why some compressional signals generated by magnetosheath ULF fluctuations remain intense earthward of the resonant flux surface [cf. Ziesolleck et al., 1996]. The resulting persistence of compressional Pc5 power at the plasmapause would also drive plasmaspheric cavity modes and thereby provide a natural source for Pc5 waves observed at low-latitude ground stations [e.g., Bloom and Singer, 1995].
Lotko William
Proehl J.
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