About the increase of HNO₃ in the stratopause region during the Halloween 2003 solar proton event

Abstract

In this paper, we explain the HNO 3 observations made with the MIPAS/Envisat instrument in the northern polar region at the time of the October‐November 2003 solar proton event. Increases of 0.5–5.5 ppbv are seen at altitudes 35–58 km after the onset of the event. Results from the Sodankylä Ion and Neutral Chemistry model are in good agreement with the MIPAS observations, except at around 58 km where the modeled mixing ratios are about a factor of two larger. According to the model results, HNO 3 production at altitudes above 35 km is almost entirely due to ion‐ion recombination between NO 3 − and H + cluster ions. At 35 km and below, there is contribution also from N 2 O 5 reacting with ions as well as from NO 2 reacting with OH.