On the possibility of ion-drag to induce dynamic instability in the lower thermosphere neutral gas

Strong wind shears may result in dynamic instability, often characterised b y the Richardson number lying between zero and 0.25. The extent to which el ectric-field driven ion flow may induce such neutral wind shears is examine d. Further, it is proposed that, in the ionosphere, it is possible for elec tric fields to drive ion winds such that the collisionally induced neutral air response may be comparable to viscous damping of neutral motion. We sha ll present an analogy to the Reynolds Number Re to quantify this effect. In the same way that Re may be used to evaluate the likelihood of a flow bein g turbulent, the analagous metric may also indicate where in the atmosphere plasma dynamics may be strong enough to destabilise the neutral dynamics.