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Letters to Nature
Nature 295, 680 (25 February 1982); doi:10.1038/295680a0

Nonlinear reflectivity of high-power radio waves in the ionosphere

H. Kopka*, P. Stubbe*, T. B. Jones & T. Robinson

*Max-Planck-Institute für Aeronomie, 3411 Katlenburg-Lindau 3, FRG
Department of Physics, University of Leicester, Leicester LE1 7RH, UK

An important result of earlier ionospheric modification experiments performed at Platteville, Colorado, was the discovery that the reflectivity of the ionosphere was greatly reduced in the reflection region of a high-power radio (pump) wave1. Because the reflectivity of low-power diagnostic waves passing through the modified region with frequencies from just below the pump wave frequency up to the F region critical frequency were reduced, the phenomenon was termed wide-band absorption (WBA). Subsequent experimental and theoretical work (for review see ref. 2) has led to the conclusion that WBA is due to the scattering of radio waves from field-aligned irregularities into plasma waves. These irregularities are generated by the interaction of the pump wave and the ionospheric plasma but the mechanism by which this occurs is not completely understood. It is evident, however, that in the process the pump wave itself undergoes WBA. In a recent campaign using the Max-Planck Institute ionospheric modification facility at Ramfjordmoen, near Tromso, Norway, the existence of WBA at high latitudes was confirmed by experiments using low-power diagnostic waves passing through the reflection region of the high-power radio wave3,4. As we report here, during an experiment to measure the effect of WBA on the pump wave itself, the essentially nonlinear nature of the interaction between the high-power radio waves and the ionosphere was demonstrated in a new and striking way.

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References

1. Cohen, R. & Whitehead, J. D. J. geophys. Res. 75, 6439−6445 (1970). | ISI |
2. Fejer, J. A. Rev. Geophys. Space Phys. 17, 135−153 (1979).
3. Jones, T. B., Robinson, T., Kopka, H. & Stubbe, P. J. geophys. Res. (in the press).
4. Stubbe, P., Kopka, H., Jones, T. B. & Robinson, T. J. geophys. Res. (in the press).



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