Through various processes molecular nitrogen within the nocturnal auroral oval is vibrationally excited, substantially increasing the rate at which O+ is lost via the reaction O++N*2→NO++N. Owing to the action of thermospheric winds and diffusion, N*2 does not remain at its point of origin but is transported to regions outside the auroral oval where it can act to substantially reduce the F-region electron density. For an equatorward transport speed of 100 m sec-1, N*2 can travel 3¿ to 4¿ of latitude before quenching with atomic oxygen substantially reduces the N*2 density. This process may contribute significantly to the formation of the mid-latitude F-region electron density trough.