Effect of Electron Precipitation on E-Region Instabilities: Theoretical Analysis*

During periods of strong geomagnetic activity, intense currents flow from the magnetosphere into the high-latitude E-region ionosphere along the magnetic field. In this region, collisions between the plasma and neutral molecules allow the entire magnetosphere-ionosphere current system to close. These same currents cause strong DC electric fields in the E-region ionosphere where they drive plasma instabilities, including the Farley-Buneman instability (FBI). These instabilities give rise to small-scale plasma turbulence that modifies the large-scale ionospheric conductance that, in turn, affects the evolution of the entire near-Earth plasma environment. Also, during geomagnetic storms, precipitating electrons of high energies, $\gtrsim$~5 keV, frequently penetrate down to the same regions where intense currents and E fields develop. This research examines the effects of precipitating electrons on the generation of the FBI and shows that, under many common conditions, it can easily suppress the FBI in a predictable manner. We expect precipitation to exert a significant feedback on the magnetosphere by preventing the elevated conductivity caused by FBI driven turbulence. This suppression should be taken into account in global modeling of the magnetosphere-ionosphere coupling.