Interannual variability in the effects of energetic particle precipitation (EPP) on the stratosphere

Odd nitrogen produced routinely in the mesosphere or lower thermosphere (MLT) by low- or medium-energy particles, or sporadically in the stratosphere by very high energy electrons or solar protons, can affect stratospheric ozone distributions. This talk focuses on the magnitude and variability of the contribution of EPP- NOx (odd nitrogen produced by EPP) to the stratosphere during the last two decades. New results from meteorological analyses, satellite-based observations, and 3D model simulations will be presented. We will show that interannual variations in the amount of EPP-NOx in the southern hemisphere stratosphere depend primarily on variability in energetic particle precipitation. In the northern hemisphere, however, meteorological variability appears to be more significant. Observations suggest that EPP contributes up to about 40 percent (10 percent) of the polar (hemispheric) NOx source in the stratosphere. We will highlight some of the gaps in our understanding of the pathways by which coupling between the stratosphere and MLT is affected by EPP, and the need for observations of NOx throughout the MLT in the polar winter.