Growth and stability of artificial ion clouds in the ionosphere

A number of instabilities that may account for sudden onset of striations in ionospheric barium clouds are considered. The E×B instability, driven by confined action of the ambient ionospheric electric field and the cloud density gradient, is shown to be the most likely cause. The equilibrium state of the cloud is obtained by an expansion technique, yielding ion density, internal electric field, and cloud velocity. The linearized small oscillation equations are then obtained and are reduced to two-dimensional form. A trial solution yields an instability threshold (expressed either as critical electric field or as onset time delay) that is of reasonable magnitude.