Electron precipitation and its impact on stratospheric ozone.

We investigate the impact of auroral electron precipitation on the chemical composition of the middle atmosphere. High energy electron flux measurements from the MEPED instrument on NOAA satellites from 1979 through 2006 are used with a parameterized auroral oval in a 28 year timeslice simulation using the Canadian Middle Atmosphere Model (CMAM), a chemistry climate model. NOx produced by ionization in the upper mesosphere and lower thermosphere can survive descent into the upper polar stratosphere under certain transport conditions in the polar night. This occurs more regularly in the southern hemisphere winter due to the strong vortex in the mesosphere. During northern hemisphere winter such transport occurs in the wake of major sudden warmings, which develop about every other year. The annual mean impact on the ozone distribution is in the 5-10% range confined to high latitudes of the southern hemisphere. In the northern hemisphere the impact is less than 5%. Short term ozone loss can be significantly greater. The impact of the ozone loss is to intensify the southern winter polar vortex. The effect on the winter polar vortex is obscured by variability.