Mesospheric and stratospheric NOy produced by energetic particle precipitation during 2002–2012

Global distributions of the six principal reactive nitrogen (NO y ) compounds (HNO 3 , NO 2 , NO, N 2 O 5 , ClONO 2 , and HNO 4 ) have been derived from midinfrared limb emission spectra taken by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board Envisat during 2002–2012. The obtained data set provides a unique climatological record of NO y in the middle atmosphere. The contribution of NO y produced by energetic particle precipitation (EPP) has been discriminated from that produced by N 2 O oxidation using a tracer correlation method based on MIPAS CH 4 and CO observations. The EPP‐NO y distributions, obtained in the vertical range 20–70km, allow to trace odd nitrogen polar winter descent from the mesosphere down to the middle and lower stratosphere, where it contributes to catalytic ozone destruction. Highest EPP‐NO y concentrations (up to 1 ppmv) are found in the winter solstice mesosphere, decreasing continuously with time and toward lower altitudes. Springtime peak concentrations of a few parts per billion by volume are observed at 22–25km, demonstrating a regular EPP impact on the entire stratosphere. The interannual variation shows a clear solar cycle signal in consonance with geomagnetic activity variations. A pronounced hemispheric asymmetry of EPP‐NO y is observed, with higher concentrations in the Southern Hemisphere (SH) and stronger variability in the Northern Hemisphere (NH). Poleward of 60°, EPP‐NO y contributes to the winter NO y column at 20–70km by 10–40% in the SH and 1–30% in the NH. Smaller contributions (0.1–1%) are found at midlatitudes (30°–60°). This study provides the first assessment of EPP‐NO y intrusions into the stratosphere based on globally available satellite data on a decadal scale.