Physics
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsm41c..07s&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SM41C-07
Physics
2708 Current Systems (2409), 2712 Electric Fields (2411), 2752 Mhd Waves And Instabilities, 2760 Plasma Convection
Scientific paper
Electromagnetic wave propagation in the surface-ionosphere waveguide has been invoked as a means for transmitting signals from high latitudes to near equatorial latitudes [Kikuchi and Araki, JATP, 41, 927-936, 1979]. The wave energy is transmitted as a transverse magnetic (TM) mode with a vertical electric field. Because this mode has no low frequency cut-off, and the attenuation of the waves in the waveguide is expected to be relatively weak, Kikuchi and Araki have argued that the surface-ionosphere waveguide is a better means for transmitting information to lower latitudes than the ionospheric (Alfvén resonator) waveguide. Thus they argue that signals associated with Sudden Commencements (SCs), as well as changes in magnetospsheric convection, will be transmitted at essentially the speed of light by the surface-ionosphere waveguide. Because of the equivalence between electrical and mechanical loads within the ionosphere, we can address questions of ionospheric convection by considering the flow of electromagnetic energy via Poynting flux. In particular, the excitation of the TM mode requires that Poynting flux flow out of the ionosphere into the waveguide. Because the currents in the E-region are primarily Hall currents, the electric field and magnetic field are nearly parallel, implying only small Poynting flux. In order to address this more completely we consider the propagation of Alfvén waves through the ionosphere. Because of the Hall term, we find that at low altitudes the waves become whistler-like in their polarization characteristics. Thus a linearly polarized wave incident on the ionosphere from above becomes right-hand circularly polarized on exiting the ionosphere below. This suggests that the signals entering the waveguide will not retain sufficient information concerning the imposed convection for that information to be transmitted to lower latitudes.
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