Numerical modeling of the drift and deformation of ionospheric plasma clouds and of their interaction with other layers of the ionosphere

The equations of ion motion and of the electric potential, which describe the behavior of a plasma cloud in the ionosphere, are solved by numerical methods, the real ionosphere being approximated by a layered model. It is found that the dominant physical processes depend on the ionospheric region into which the cloud is released. In the E layer the main process is a continuous exchange of the ions constituting the perturbation, which results in the original cloud ions becoming imbedded in the ionosphere and drifting with it. The perturbation thereby moves like a wave through the ionosphere. In the F region the exchange process is very slow, and distortion of the cloud by self-generated electric polarization fields becomes the dominant effect. A comparison of the computed distortion with observations on barium plasma clouds suggests that electrostatic coupling between the E and F layers, over the scale size of the ion clouds, is usually not very efficient. The effects of an altitude dependent neutral gas wind and of ionospheric recombination processes have been examined. The altitude dependent neutral gas wind produces profound distortion in the cloud, but the ionospheric recombination processes appear to have no important quantitative effect. If small perturbations are introduced into the initial cloud distribution, they develop into fingers that closely resemble the observed striations in barium ion clouds. In the E region the perturbations are shed from the ion cloud into the ionospheric positive image cloud.