Unusual meteorological conditions in early 2009 led to more ozone-destroying gases in the middle atmosphere
October 7, 2009 - Energetic particle precipitation, in which high-energy electrons and protons from the Sun and magnetosphere hit Earth's upper atmosphere, results in the production of nitrogen oxides (NOx) in the mesosphere and lower thermosphere. Under the right weather conditions, NOx can descend into the stratosphere, where it destroys ozone. Randall et al. (2009) describe observations that show that in early 2009, the amount of NOx that descended into the middle atmosphere above the Arctic was about 50 times higher than usual. They argue that the high level of NOx resulted not from increased energetic particle precipitation (which was actually below average at the time) but from unusual meteorological conditions that allowed more NOx to reach the middle atmosphere. The authors note that 2009 is the second time on record in recent years when abnormal weather conditions led to increased descent of NOx in the polar region. They suggest that this may indicate that changes are occurring in the atmosphere and point to a need for better understanding of the interaction between meteorology and space weather.
Randall, C.E., V.L. Harvey, D.E. Siskind, J. France, P.F. Bernath, C.D. Boone, and K.A. Walker (2009), NOx descent in the Arctic Middle Atmosphere in early 2009, Geophysical Research Letters, Vol. 36, L18811, doi:10.1029/2009GL039706 (PDF).