1 The Mid-Latitude F Region at the Mesoscale

Almost no new theoretical work has been conducted in the area of mid-latitude F-region plasma instabilities since Perkins ’ [1973] linear theory. New experimental data now suggest that the nonlinear development of mid-latitude F-region structures includes large polarization electric fields which dominate the final state. Airglow and radar data show that the height-integrated conductivity (SP) is greatly depleted in some regions, which is in agreement with a polarization hypothesis. A simple model taking into account the finite meridional extent of the structures yields a wind-driven poleward perturbation electric field many times larger than the ambient electric field. Secondary E´B instabilities arise due to these large electric fields and the gradients in SP. The question of pre-seeding of the primary several hundred kilometer scale wave packets remains open. However, it appears that gravity waves may generate electric fields more easily than was previously thought