Abstract
ELLIS1,2investigated the condition in the ionosphere under which an upgoing ordinary radio wave is converted, through a coupling process, into an upgoing extraordinary wave in the Z mode. (Propagation in the Z mode requires the presence of both an ionised gas and a magnetic field; hence such waves cannot be received in free space.) This occurs for a wave incident on the ionosphere from below with its wave normal close to a critical direction in the magnetic meridian plane. This direction is such that when the wave reaches the level where X = 1, which is normally a complete reflector for the ordinary wave, its wave-normal direction has become close to the magnetic field line direction. The symbols X and Y are as usually defined in magnetoionic theory (see Ratcliffe3). The level X = 1 becomes semi-transparent for a cone of angles centred on the critical direction. This cone is called the ‘Ellis window’. The Z-mode waves are reflected at a higher level where X = 1+Y. Here I wish to draw attention to a window which is relevant to the escape of Z-mode radiation produced naturally in the topside ionosphere
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References
Ellis, G. R. A., J. atmos. terr. Phys., 8, 243 (1956).
Ellis, G. R. A., Nature, 193, 862 (1962).
Ratcliffe, J. A., Magnetoionic Theory (Cambridge, 1959).
Mosier, R. M., Kaiser, M. L., and Brown, L. W., J. geophys. Res., 78, 1673 (1973).
Gurnett, D. A., J. geophys. Res., 79, 4227 (1974).
Jorgensen, T. S., J. geophys. Res., 73, 1055 (1968).
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JONES, D. The second Z-propagation window. Nature 262, 674–675 (1976). https://doi.org/10.1038/262674a0
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DOI: https://doi.org/10.1038/262674a0
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