EVOLUTION OF PLASMA BUBBLES IN THE EQUATORIAL F-REGION WITH DIFFERENTSEEDING CONDITIONS

As there are a significant number of observed onset conditions for the post-sunset equatorial spread F that are not evidently associated wit h the required (5%) seed perturbation as assumed by the earlier simula tion studies, an investigation is carried out with different seeding c onditions for the evolution of plasma bubbles in the equatorial F regi on by means of a nonlinear numerical simulation model. The present inv estigation reveals that even an order of magnitude less perturbation ( 0.5%) than the earlier belief, grows into a bubble provided the nonlin ear effects of other agencies such as the vertical wind and the electr ic field, in addition to gravity are taken into account. It is suggest ed that the above amplitude of the initial perturbation in plasma dens ity can be generated through electrodynamical effects by the observed fluctuations in the electric fields.