Atmospheric Chemistry Experiment (ACE) Arctic stratospheric measurements of NOxduring February and March 2004: Impact of intense solar flares

Abstract

[1] Solar occultation measurements recorded in the Arctic by the Atmospheric Chemistry Experiment (ACE) Fourier transform spectrometer show elevated volume mixing ratios of NO and NO2 in the upper stratosphere from mid-February to late March 2004. Mixing ratios of NO exceeded 1.3 ppmv (10−6 parts per million by volume) during mid-February and are higher than any values previously reported in the Arctic during late winter and early spring. The elevated NOx (NO + NO2) mixing ratios likely resulted from particle emissions by intense solar flares that occurred the previous October and November followed by NOx production and downward transport to the upper stratospheric vortex where the elevated levels persisted due to the long lifetime of NOx during darkness in polar winter and early spring. The descent and the NOx decrease rates in the upper stratospheric vortex are estimated from an analysis of the time series. The measured descent rate is compared with previous observations and model predictions.