Deformation and striation of plasma clouds in the ionosphere. 1

We derive the equations that govern the nonlinear motion of plasma clouds in the ionosphere, including the effects of finite temperature and resistivity along the magnetic field lines. The principal application is to large barium clouds, which contain enough plasma to dominate the integrated Pedersen conductivity on lines of force that pass through the cloud and are sufficiently high so that Ωi/νin ≫ 1. Approximate solutions to the nonlinear equations in simplified geometries show that the plasma clouds deform in a manner that qualitatively agrees with observations. Numerical solutions are presented in a companion paper. Finite resistivity along the magnetic field has two effects. First, it governs the short-wavelength limit for striations. Second, for small plasma clouds (those whose contribution to the height-integrated conductivity is small), finite resistivity requires that a substantial electric field be present (∼10² mv/m) in order that the growth rate for striations circumvent a reduction by the short-circuiting effect.