Parametric coupling processes of a large-amplitude electromagnetic pump wave with convective plasma fluid instabilities (E¿B gradient drift and current convective) in the high-latitude F region ionosphere have been studied. We find that a pump wave, with frequency near the upper hybrid frequency and with electric field component perpendicular to the ambient magnetic field, can stabilize or destabilize the E¿B gradient drift and/or current convective instability. For parameters typical of the nighttime high-latitude F region ionosphere we find stabilization or destabilization with a vertically incident O mode carrying a free space incident power density of the order of 10-4 W/m2.