Vortexwide denitrification of the Arctic polar stratosphere in winter 1999/2000 determined by remote observations

Abstract

[1] Denitrification has been studied using measurements of stratospheric HNO 3 and N 2 O by the Airborne Submillimeter Radiometer (ASUR), operated on board the NASA DC-8 during SOLVE/THESEO 2000. Lidar measurements taken on board the same aircraft have been used to distinguish between temporary uptake of HNO 3 in polar stratospheric clouds (PSCs) and denitrification events. To derive an NO y budget, ClNO 3 data by balloonborne and ground-based Fourier transform infrared measurements and a model estimate of NO x + 2N 2 O 5 have been considered. The HNO 3 profiles of sporadic ASUR measurements without PSC coverage in January suggest that denitrification had started in the vortex core region by then. Vortexwide denitrification was found in midMarch 2000. Corrected for diabatic descent using the N 2 O measurements, a vortexaveraged NO y deficit between 1.2 ± 0.9 ppb at about 16 km altitude and 5.3 ± 2.7 ppb at about 20.5 km altitude was derived compared to December 1999, based on an observed decrease in HNO 3 between 2.2 and 3.5 ppb during this time period. A shift in the NO y partitioning from HNO 3 toward ClNO 3 of about 0.4 to 0.7 ppb was observed in midMarch compared to December, indicating that chlorine deactivation was occurring. Comparisons with the SLIMCAT three-dimensional chemical transport model applying denitrification schemes based on ice and nitric acid trihydrate particles in equilibrium, respectively, reveal agreement within the error bars at higher altitudes ($19 km) but show discrepancies at lower altitudes ($16 km). It is suggested that more sophisticated denitrification schemes are needed to generally describe denitrification processes.

Factors controlling Arctic denitrification in cold winters of the 1990s

“…In situ measurements of NO y and HNO 3 aboard the ER-2 aircraft made in mid-March 2000 showed widespread denitrification had taken place over a large alititude range compared with early December 1999 (Popp et al, 2001;Kleinböhl et al, 2002). Satellite observations of HNO 3 at 465 K also showed that the denitrification persisted long after temperatures rose above the PSC threshold in early March 2000 (Santee et al, 2000).…”

“…Extensive denitrification was observed in 1999/2000 by both in situ (Popp et al, 2001) and remote (Santee et al, 2000;Kleinböhl et al, 2002) instruments. Large nitric acidcontaining particles (10 to 20 µm diameter) at low number concentrations (between 10 −5 and 10 −3 cm −3 ) were measured by the NOAA NO y instrument aboard the NASA ER-2 aircraft in the 1999/2000 winter Arctic vortex and have generally been inferred to be NAT (Fahey et al, 2001;Northway et al, 2002a).…”

“…tions? There are observations of denitrification in each of the cold winters 1994/5 (Sugita et al, 1998;Waibel et al, 1999/6 (Hintsa et al, 1998Dessler et al, 1999), 1996/7 (Kondo et al, 2000Irie et al, 2001) and 1999/2000 (Santee et al, 2000;Popp et al, 2001;Kleinböhl et al, 2002). See also Santee et al (1999) for MLS measurements of denitrification between 1991 and 1998.…”

Implementing growth and sedimentation of NAT particles in a global Eulerian model

“…More recently, during the Arctic winter of 1999/2000, which is one of the coldest currently on record (Manney and Sabutis, 2000), both extensive nitrification (Koike et al, 2002) and denitrification (Popp et al, 2001;Santee et al, 2000;Kleinböhl et al, 2003) were observed. Again, large ozone loss was also derived for this winter using both model experiments (Sinnhuber et al, 2000) and in-situ observations of ozone (Richard et al, 2001).…”

“…Chipperfield, 1999; Koike et al, 2002). Several of these model studies have concluded that such a simple parameterization of denitrification maybe inadequate for modelling Arctic wintertime ozone loss (Kleinböhl et al, 2003;Sinnhuber et al, 2000). Therefore, agreement between model results and observations may simply be fortuitous.…”