These results suggest that power beam dispersion due to ionospheric density fluctuations, ambient or nonlinearly induced, will be such as to increase field intensity at the edges of the beam by 15 to 27 percent, which at the low nominal power densities does not contribute to significant loss. 3. 4 IONOSPHERIC MODIFICATION BY HIGH POWER IRRADIATION Ionospheric modification experiments conducted during the last three years at Platteville, Colorado and Arecibo, Puerto Rico have shown that relatively modest HF power fluxes can produce significant changes in the thermal energy of the plasma in the , and regions. (12) Moreover, one finds that incident power fluxes intense enough to modify the ionospheric energy balance through ohmic heating can also cause self-focusing instabilities which produce substantial field-aligned density perturbations and an overall F-layer electron density depletion of several percent. Results of recent D-region experiments also suggest, although not conclusively, that HF heating can reduce recombination and thereby increase the electron density during the day (see Appendix C). One can attempt to estimate the effects of high power microwaves by noting that ohmic dissipation scales as the reciprocal of the square of the electromagnetic frequency. At radio wave frequencies , fluxes of at F-layer heights and in the D and E regions produce significant changes. Therefore, one would expect that microwave power den- sities of might produce similar effects. The direct effect on high power microwave transmission is likely to be small since the absorption at these frequencies remains negligible even if we expect an order of magnitude increase in electron temperature and density. However, power densities in excess of could produce large horizontal electron density gradients that could cause significant beam displacement and dispersion.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==