[1] Measurements from several different satellite instruments are used to estimate effects of energetic particle precipitation (EPP) on NO x (NO + NO 2 ) in the Southern Hemisphere stratosphere from 1992 to 2005. The focus is the EPP Indirect Effect (IE), whereby NO x produced in the mesosphere or thermosphere via EPP (EPP-NO x ) descends to the stratosphere during the polar winter, where it can participate in catalytic ozone destruction. EPP-NO x entering the stratosphere is found to vary in magnitude from 0.1 to 2.6 gigamoles per year, with maximum values occurring in 1994 and 2003. The interannual variation correlates strongly with several measures of EPP activity, including auroral and medium energy electron hemispheric power, and satellite measurements of thermospheric NO. This represents the first estimation of EPP-NO x contributions to the stratospheric odd nitrogen budget using observations over an entire solar cycle. The results will be useful for evaluating and constraining global models to investigate coupling of the upper and lower atmosphere by the EPP IE, including any influences this might have on ozone trends and possibly on climate.

Measurements from the Atmospheric Chemistry Experiment show pronounced downward transport of NOx (NO+NO2) to the Arctic stratosphere in Feb–Mar 2006. NOx mixing ratios in the upper stratosphere were 3–6 times larger than observed previously in either the Arctic or Antarctic, aside from the extraordinary winter of 2003–2004. There was only minimal geomagnetic activity in late 2005 and early 2006, however, suggesting that NOx produced via energetic particle precipitation was not significantly elevated. On the other hand, the Arctic polar vortex at stratopause altitudes in Feb 2006 was exceptionally strong, implying greater confinement of air in the polar night. Carbon monoxide data also indicate enhanced confined descent of air from the mesosphere. These results confirm that impacts of EPP on the atmosphere are modulated by meteorological conditions; this has implications for understanding interannual variability and trends in stratospheric NOx and ozone.

[1] During the last decade, much attention has been placed on quantifying and modeling Arctic stratospheric O 3 loss. At issue in particular is the reliability of models for simulating the loss under variable dynamical conditions in the Arctic region. This paper describes