Tidal dynamics and composition variations in the thermosphere

The effects of mutual diffusion between O and N 2 are examined for diurnal and semidiurnal tidal oscillations in the thermosphere. A binary gas extension of a previous f plane equivalent gravity wave formalism is developed and utilized to study this effect. Compared with calculations that omit O‐N 2 mutual diffusion, diffusive interaction affects the temperatures and horizontal velocities associated with the diurnal thermospheric tide excited in situ by less than 10% with negligible shifts in phase, and by roughly 20–40% the semidiurnal tide excited in situ, and the (2, 2) and (2, 4) modes propagating from the mesosphere, accompanied by 1‐ to 4‐hour shifts in phase. These results affect the interpretation of incoherent scatter measurements of thermospheric tides and the construction of synthesized tidal models that are calibrated by the measurements and suggest that the inequality of the vertical transport velocities of O and N 2 be accounted for in three‐dimensional numerical models of semidiurnal thermospheric tides.