Here we use satellite observations from the ACE-FTS, MLS/Aura and SABER/TIMED to study the effects of solar proton events (SPEs) and strong sudden stratospheric warmings (SSWs) on the middle atmospheric odd nitrogen (NOx) and ozone levels in the Northern Hemispheric polar region. Three winters (January–March) are considered: (1) 2005 (SPE), (2) 2009 (SSW), and (3) 2012 (SPEs and SSW). These different cases provide a good opportunity to study the roles that transport from the mesosphere-lower thermosphere region and in situ production due to particle precipitation have on stratospheric NOx levels and the consequent effects on the middle atmospheric ozone. The observations show increases in NOx after both the SPEs (days to weeks) and SSWs (weeks to months) by up to a factor of 25 between 40 and 90 km. The largest mesospheric NOx increases are observed following the SSW in late January 2009, but the most substantial effects in the upper stratosphere are seen when both an SSW and in situ production by SPEs take place (2012), even though the in situ NOx production in 2012 was relatively weak in magnitude compared to periods of much higher solar activity. In 2012, both short-term (days, due to SPEs and odd hydrogen) depletion and longer-term (months, due to several drivers) depletion of ozone of up to 90% are observed in the mesosphere and upper stratosphere, coinciding with the enhanced amounts of NOx.
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