A model study of the stratospheric budget of odd nitrogen, including effects of solar cycle variations

A two-dimensional diabatic circulation model of the stratosphere and the troposphere is used to study the budget of total odd nitrogen (NO^y) and to simulate the response of odd oxygen and nitrogen species to the 11-year solar cycle variations. Firstly the results are discussed in terms of influence regions of the various NO^y production processes including surface sources (anthropogenic sources, soil exhalation), lightning, N₂O oxidation, galactic cosmic rays (GCRs) and high-latitude input from the thermosphere and mesosphere. Although the N₂O oxidation process is the dominant odd nitrogen source throughout the stratosphere, NO_y produced within the thermosphere and transported through the stratopause at high latitude during winter, may affect NO_y distribution, particularly during periods of large solar activity. In the lower stratosphere, the lightning contribution becomes significant (about 60% and 30% at the local tropopause in equatorial and polar regions, respectively). The GCR contribution is found to be rather weak even at the high-latitude tropopause (about 10%). Input parameters which vary with the solar cycle include ultraviolet photon fluxes, GCRs and downward flux at the high-latitude winter stratopause. The effect of the thermospheric production is confined to the high and middle polar stratosphere. We find, for instance, less than 4% variations in NO_y at 19 km in the winter hemisphere, where the main effect from solar cycle variations stems from changes in photon fluxes. Increases in photon fluxes lead to less NO_y production.