Three-dimensional equilibrium and stability of ionospheric plasma clouds

The equilibrium and stability of three-dimensional (3-D) ionospheric plasma clouds is investigated. The equilibrium density profile is assumed to be a 3-D water bag with a circular cross section transverse to B, and an ellipsoidal cross section parallel to B. The equilibrium potential consists of two parts: a polarization potential driven by a uniform neutral wind, and an ambipolar potential driven by parallel electron pressure. The latter potential is shown to cause sheared azimuthal plasma flows perpendicular to B. A stability analysis of this equilibrium is carried out. It is found that the E×B instability, which causes the structuring of ionospheric plasma clouds, can be stabilized by the shear in the azimuthal flow. A marginal stability criterion is derived. On the basis of this stability criteria, striations of barium clouds in the ionospheric F region should be stable to further bifurcation, as is observed