Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm11c1172s&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #SM11C-1172
Physics
2487 Wave Propagation (6934), 2736 Magnetosphere/Ionosphere Interactions, 2752 Mhd Waves And Instabilities
Scientific paper
The waveguide formed by the Earth's surface and the ionosphere has been postulated as a means for transmitting information rapidly across field lines. If the waveguide can be excited, then this may explain the ``prompt'' response of the ionosphere to changes in solar wind drivers, where the nightside ionosphere appears to react more quickly than would be expected for a purely magnetospheric driver of convection. Previous analysis of wave propagation into the waveguide suggests that for vertical propagation very little electromagnetic energy, as measured by the Poynting vector, passes through the highly dissipative ionosphere. The simplifying assumption of vertical propagation neglects the fact that the fast mode wave becomes evanescent along the field line for sufficiently short perpendicular wavelength. Because of the very high Alfvén speed this wavelength need only be of the order 1000 km (longer for lower frequencies) for the fast mode to be evanescent. We have therefore explored the transmission of electromagnetic energy for oblique propagation. The degree to which electromagnetic energy flows into the surface-ionosphere waveguide depends on the assumed incident wave mode, and whether or not the wave is assumed to be evanescent across the field. The perpendicularly evanescent mode corresponds to a Laplace transform of the incident signal, which might better represent an impulse than the harmonic (or Fourier mode) assumption. Preliminary analysis suggests that the perpendicularly evanescent fast mode carries the greatest amount of electromagnetic energy into the waveguide, but further analysis is required to determine if this is sufficient to act as a generator for magnetospheric convection.
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