NOx enhancements in the middle atmosphere during 2003-2004 polar winter: relative significance of solar proton events and the aurora as source

In this study we combine odd nitrogen (NOx) observations from the GOMOS and POAM III instruments with a radio wave ionization index to provide a detailed description of the generation and descent of polar NOx into the upper stratosphere during the Northern Hemisphere winter of 2003-2004. The measurements are used to study the relative contributions of ionization due to solar proton events, energetic electron precipitation, and low-energy (1-10 keV) electron precipitation on NOx production, and its subsequent downward transport to the upper stratosphere. We show that NOx generated from the large solar proton storm in October/November 2003 was transported into the upper stratosphere in agreement with model calculations, but that aurorally generated NOx also descended later in the winter. Both periods were highly significant and produced large long-lived decreases in stratospheric ozone once it arrived at those altitudes. The observations made by GOMOS deep into the nighttime polar vortex are critical in differentiating between the stratospheric effects of these two events.

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