Theoretical models of the coupled ionosphere‐plasmasphere system have been investigated with respect to processes occurring in the nighttime F2 layer. It is found that plasma flow from the plasmasphere into the ionosphere has a strong stabilizing influence upon the peak F2 region ion density NmF2 such that for wide ranges of applied east‐west electric fields or north‐south thermospheric winds there is essentially no change in the maximum density of the F2 layer (NmF2). It is also found that NmF2 depends sensitively upon the plasma density of the plasmasphere and upon the neutral hydrogen concentration in the thermosphere. Time‐dependent processes have been studied also by using step function electric fields and neutral winds. In the electric field case, squeezing of thermal plasma out of the plasmasphere along a contracting field tube significantly affects NmF2. Neutral thermospheric winds, on the other hand, have little effect on nighttime NmF2.

Radiation from electrical power lines leaks into the magnetosphere and stimulates strong very-low-frequency wave activity out to many earth radii. Observations in Antarctica show that wave activity induced by power lines tends to occur during the daytime when power consumption is high in the source region in eastern Canada. The wave frequency ranges from 1 to 8 kilohertz. This man-made wave activity may have significant effects on energetic electrons trapped in the earth's radiation belts.

Theoretical models have been used to investigate the effects of artificially injected H2 gas on plasma densities in the ionospheric F region and the overlying protonosphere. Owing to large reaction rates between H2 and ionospheric O+ ions, plasma densities in both daytime and nighttime ionospheres can be greatly reduced by modest amounts of H2 gas released. 100 kg of H2 released at 300 km altitude reduces local O+ densities by more than three orders of magnitude and produces ∼5% depression in H+ densities in the overlying protonosphere. These results suggest that it should be possible to conduct controlled chemical modification experiments for investigation of many outstanding ionospheric and magnetospheric problems.

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