Transport of thermospheric NO_X to the stratosphere and mesosphere

Odd Nitrogen (NO_X) is produced in the Earth's thermosphere when N₂ is dissociated by solar radiation and energetic particle precipitation. Thermospheric production and downward transport in winter high latitudes gives rise to a polar reservoir containing very large quantities of NO_X. This reservoir, which is maintained throughout the winter, can affect the photochemistry of the upper stratosphere and mesosphere. In particular, it can account for variations in the ozone concentration in the stratosphere associated with the 11-year solar cycle, and for the smooth and sporadic D-region winter anomalies. The results of numerical modeling studies bearing on these phenomena are compared with observations to ascertain the impact of the thermospheric NO_X source on lower levels of the middle atmosphere.