Modification of the high latitude ionosphere by high power radio waves.
2015-11-19T09:17:37Z (GMT) by
The results of experiments to investigate the effects of high power radio waves on the high latitude ionosphere are presented. The experiments entailed probing the modified F-region with low power diagnostic radio waves. Measurements of the amplitude, phase and spectral content of the diagnostic signals yield information regarding the spatial and temporal structure of large-scale, predominantly isotropic irregularities and small-scale strongly field aligned irregularities induced in the ionospheric plasma by the high power radio waves. By monitoring the signal from the ionospherically reflected high power radio wave itself it was also possible to study directly the nonlinear properties of ionospheric reflectivity. The experimental observations indicate that anomalous absorption of electromagnetic waves, due to scattering from small-scale field-aligned irregularities, plays an important role in the ionospheric modification process at high latitudes. However, it is necessary to modify current theories of anomalous absorption to take full account of the effect of the geomagnetic field. As a result, the scale lengths of small scale irregularities have been determined for the first time. Other new results include, the first direct observations of a hysteresis effect in anomalous absorption and the first observations of F-region cross modulation. Both of these phenomena have also been treated theoretically. It has been demonstrated that, in addition to providing new information concerning nonlinear plasma phenomena caused by high power radio waves, the ionospheric modifications technique also enables parameters such as the recombination rate and the thermal conductivity of the natural ionosphere to be deduced.