Effects of energetic particle precipitation on the stratosphere: Solar cycle variability

It is now well documented that nitric oxide produced in the thermosphere or mesosphere by energetic particle precipitation (EPP-NOx) can descend in the polar night to the stratosphere, where it participates in catalytic ozone destruction. This talk focuses on the magnitude and variability of this coupling during the last two decades. The two factors controlling EPP-induced thermosphere/stratosphere coupling include the numbers and energies of precipitating particles, which determine the amount and altitude of NOx produced, and the efficiency with which the NOx is transported downward. This is because NOx transported out of the polar night before reaching the lower mesosphere is usually destroyed via photodissociation of NO. We will show recent work that suggests that in the southern hemisphere, solar cycle variability in the amount of EPP-NOx reaching the stratosphere depends primarily on variability in the first factor. In the northern hemisphere, however, the second factor – variations in meteorology – appear to be more significant for driving solar cycle variability in the coupling.