Downward transport of upper atmospheric NO_x into the polar stratosphere and lower mesosphere during the Antarctic 2003 and Arctic 2002/2003 winters

Abstract

Pronounced upper stratospheric and mesospheric NOx enhancements were measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) in the Southern Hemisphere (SH) polar vortex from May to August 2003, reaching average abundances of 60 ppbv at 50–60 km in July. Peak mixing ratios of around 200 ppbv were measured in the polar night, representing the highest values ever recorded in the SH. The observed NOx enhancements are attributed to production by electron precipitation in the upper mesosphere and lower thermosphere and subsequent descent with the meridional circulation. Using measured CH4 and CO distributions as dynamic tracers, the downward transport of NOx‐rich air masses into the lower and middle stratosphere has been investigated. Upper atmospheric air with average NOx abundances of 15 ppbv reached the 800–1000 K potential temperature region (around 30 km) by the end of July, where it remained until the final warming in late October. The NOx descent was confined to the polar vortex, although significant mixing of tropical and NOx‐rich vortex air masses began already in August above 40 km. The amount of upper atmospheric NOy measured inside of the SH vortex in late spring was 1.1 Gigamoles (GM) which is in good agreement with previous estimates from HALOE data. The global coverage of MIPAS data further allows to quantify the upper atmospheric NOx dispersed into the stratosphere during August‐September, estimated in 1.3 GM. The net deposition of NOx into the stratosphere during the 2003 Antarctic winter (2.4 GM) makes up 9% of the N2O oxidation source in the SH, twice as much as estimated in previous studies. NOx and tracer distributions observed on several days during the NH winter 2002/2003 have been analyzed for comparison. We found that high planetary wave activity, resulting in the major midwinter warming had led to a rather inefficient NOx downward transport with negligible deposition of NOx into the lower and middle stratosphere.

Solar Influence on Global and Regional Climates

“…SEPs are directed towards Earth poles by the geomagnetic field where they generate nitrates on hitting Earth's atmosphere as demonstrated, for example, in observations by Mlynczak et al (2003). These nitrates are seen to migrate downwards over time (Siskind et al 2000;Funke et al 2005), resulting in catalytic destruction of stratospheric ozone (Callis et al 2000). Large SEP events generate considerable transient polar ozone depletions, which persist in winter until UV irradiance of the polar stratosphere resumes (Jackman et al 2006(Jackman et al , 2008Randall et al 2005Randall et al , 2007.…”

Variability of NO<sub>x</sub> in the polar middle atmosphere from October 2003 to March 2004: vertical transport vs. local production by energetic particles

“…The impact of solar proton events is nowadays reasonably well understood, in part thanks to the series of very large solar proton events during the maximum of solar cycle 23 (Jackman et al, 2001Funke et al, 2011;Rohen et al, 2005). There is also evidence of a large indirect effect of energetic electron precipitation for many polar winters now (Randall et al, 2006Funke et al, 2005a).…”

NO<sub><i>y</i></sub> production, ozone loss and changes in net radiative heating due to energetic particle precipitation in 2002–2010

“…Data products from the retrieval processor built and operated by the Institute of Meteorology and Climate Research (IMK) at the Karlsruhe Institute of Technology (KIT) in cooperation with the Instituto de Astrofísica de Andalucía (IAA-CSIC) (von Clarmann et al, , 2009 Clarmann et al (2013). The retrieval of NO and NO 2 is described in Funke et al (2005Funke et al ( , 2014a. Updates in the ozone retrieval scheme since von Clarmann et al (2013) are documented in Laeng et al (2014).…”