Dipole Measurements of Waves in the Ionosphere

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Abstract

The theory of distributed dipole antennas in magnetoplasmas has been tested through the analysis of the data from the two-point propagation experiment OEDIPUS C (OC). The transmission of electromagnetic signals over a 1-km distance in the ionosphere has been used to substantiate the theory of emission, propagation and detection of waves in a cold magnetoplasma. Confirmations and insights about the dipole theory arising from the OC research results have occasioned a return to some older data that can be profitably interpreted with them. The concept of dipole effective length L eff has been re-examined quantitatively with the help of the reciprocity principle. It is found that previous measurements of electromagnetic whistler-mode propagation give L eff values similar to those predicted using a classic reciprocity definition brought over from the vacuum dipole theory. In contrast, OC investigations found that L eff can be many times the dipole physical length for propagation near the whistler-mode resonance cone. The finding has important consequences for the interpretation of the measured strength of the radio emission auroral hiss and, by extension, the nature of its source. Since intra-ionospheric experiments on propagation near either the lower- or the upper-oblique-resonance cone produced extremely strong transmission, the L eff applied to the interpretation of the strength of plasma-wave phenomena in the corresponding frequency domains must be chosen with care.