Deformation and striation of plasma clouds in the ionosphere, 3. Numerical simulations of a multilevel model with recombination chemistry

Improved numerical simulations of the dynamical evolution of F region plasma clouds are presented. The improvements consist of (1) the addition of an E region with and without recombination chemistry, (2) a spatial resolution better by a factor of 2, and (3) a spatially varying mesh that almost completely removes the effects due to boundaries of the computational region. The artificially close boundaries often employed in other simulation studies produce erroneous deformations of plasma clouds and inhibit the growth of striations. The improved resolution allows very small perturbations on the backside of a plasma cloud to grow into large amplitude striations with steep protruding faces that develop indentations which cleave into daughter striations; i.e., qualitatively new phenomena appear in the simulation results. Several simulation results rich in striation phenomena are presented. When recombination processes are slow (or nonexistent), the developing F region perturbations are quickly imprinted in the E region and are fed back to the F region to enhance the process of striation formation at the edge of the cloud. When recombination processes are fast, this feedback at early times is impeded, but ion density protuberances continue to steepen and at later times cleave as a result of the interaction with the E region.