A WIND-DRIVEN GRADIENT DRIFT MECHANISM FOR MIDLATITUDE E-REGION IONOSPHERIC IRREGULARITIES

We propose a new explanation for medium- to small-scale irregularities in the mid-latitude E region. We show that the very wind field that f orms thin layers of ionization can also create plasma instabilities. T o date, the application of gradient drift instability theory has been restricted to free energy sources involving the ambient electric field . We show that a vertical shear in the zonal wind not only leads to la yer formation, but also to unstable regions on both sides of the layer . The mechanism thus does not suffer from the problem inherent in elec tric field-driven processes, namely, that the mapping of electric fiel ds along magnetic field lines leads to stabilizing conditions on one s ide of the layer, even if the other side is unstable. Evidence is give n that anomalous diffusion due to such waves affects the evolution of the layers.