Modeling the effect of denitrification on Arctic ozone depletion during winter 1999/2000

Abstract

[1] We have used the SLIMCAT three-dimensional chemical transport model together with observations from the Stratospheric Aerosol and Gas Experiment (SAGE III) Ozone Loss and Validation Experiment (SOLVE) and the Third European Stratospheric Experiment on Ozone (THESEO 2000) to quantify the effect of denitrification on Arctic ozone loss. We have used two different denitrification schemes in the model: one based on the sedimentation of ice particles containing cocondensed nitric acid trihydrate (NAT) and the other based on large NAT particles. The model was forced using both UK Meteorological Office (UKMO) and European Centre for Medium-Range Weather Forecasts (ECMWF) analyses. In the Arctic lower stratosphere the UKMO analyzed temperatures are similar to the ECMWF, except at temperatures near the ice point where the UKMO analyses are colder by over 2 K. Consequently, the UKMO analyses predicted large regions of ice clouds, in contrast to the ECMWF. The denitrification scheme based on large NAT particles gives the best agreement with ER-2 NO y observations for both sets of meteorological analyses. Although the ice scheme and UKMO analyses also produce denitrification, the vertical extent of denitrification and renitrification does not agree as well with the observed NO y . Uncertainties in the budget of ClO y observations from the ER-2 prevent an indirect validation of the best model denitrification scheme based on these data. The denitrified model runs give the best agreement with the observed HCl and ClONO 2 reservoirs in mid March. However, UKMO-forced runs generally overestimate the observed ClO x during the same period. The denitrified model runs indicate that by late March 56-74% O 3 loss had occurred at 460 K and that denitrification contributed 21-30% of this loss. The model runs showing the largest O 3 depletion (forced by UKMO analyses) agree well with ER-2 and ozone sonde data, although these runs overestimated ClO x .

Spatial, temporal, and vertical variability of polar stratospheric ozone loss in the Arctic winters 2004/2005–2009/2010

“…The composition of liquid aerosols is calculated analytically (Luo et al, 1995). The ice particles are assumed to incorporate HNO 3 in the form of NAT described by a bimodal size distribution (Davies et al, 2002). Cl y and Br y are explicitly calculated from their long-lived sources at the surface and are therefore time dependent.…”

Early unusual ozone loss during the Arctic winter 2002/2003 compared to other winters

“…The vertical transport is derived from ECMWF vertical winds. SLIMCAT simulations are performed with a recent version in which ozone fields are extended down to the troposphere on hybrid σ −θ coordinate (Feng et al, 2005). The model is forced by ECMWF analyses (instead of UKMOUnited Kingdom Met.…”

“…Ice is assumed to incorporate NAT as a co-condensate, removing nitric acid from the vapour phase. A simple NAT-based denitrification scheme is used (see Davies et al, 2001;Feng et al, 2005). SLIMCAT was initialized on 1 December 2002 from an ECMWF-forced multi-annual run which started in 1989.…”

Comparisons of polar processing diagnostics from 34 years of the ERA-Interim and MERRA reanalyses

“…Previous studies have recognized the importance of understanding the sensitivity of polar processing and ozone loss quantification to different data sets: Davies et al (2002) showed that two SLIMCAT chemical transport model (CTM) runs driven by horizontal winds and temperatures from the ECMWF (European Centre for Medium-Range Weather Forecasts) and Met Office DAS led to significantly different patterns of denitrification and chlorine activation and consequently large differences in ozone loss of nearly 20 %. Similarly, Santee et al (2002) found significant discrepancies in PSC formation and composition between model runs that used Met Office temperatures with and without a 3 K reduction.…”