Chemistry‐transport model comparison with ozone observations in the midlatitude lowermost stratosphere

Abstract

Abstract.About 600 ozone sonde profiles and in situ ozone observations on 2300 aircraft flights were compared with several three-dimensional global chemistrytransport models, in the midlatitude lowermost stratosphere during 1996. The models use the same top boundary conditions and parameterized ozone chemistry.The comparisons show that the models using general circulation model (GCM) winds do not capture the seasonal ozone accumulation in the lowermost stratosphere. The models using winds from the European Centre for Medium-Range Weather Forecasts (ECWMF) overestimate ozone above this maximum, especially during spring. This overestimation increases with increasing latitude. Close to the tropopause. the best agreement between models and observations is found during •vinter and the worst occurs during summer, where most models underestimate the mean ozone concentration. This underestimation is partly caused by inaccurate description of the relatively small-scale transport processes, mainly associated with convective activity, and partly by incomplete ozone chemistry in the parameterized scheme. The models that use assimilated winds show significant differences in calculated ozone, despite their common source (ECWMF) to calculate the transport. We illustrate that the model performance significantly depends on the ECWMF processing method and that interpolation of wind data should be avoided. In addition, the results seem relatively insensitive to vertical resolution. To improve the model performance further in this region, the horizontal resolution should be higher than 2.5 ø .

An evaluation of the performance of chemistry transport models by comparison with research aircraft observations. Part 1: Concepts and overall model performance

“…Primary production of OH radicals in the UT/LS region depends not only on O 3 and H 2 O levels but also on carbonyls and peroxides whose concentrations are again strongly linked to vertical transport and mixing (Jaeglé et al, 2001;Brühl et al, 2000;Prather and Jacob, 1997). Finally, due to the relatively long lifetimes and steep vertical gradients of many compounds in the UT/LS region small inaccuracies in the advection scheme may significantly affect their concentration levels (Bregman et al, 2001). The downward flux of ozone from the stratosphere to the troposphere is particularly sensitive to the formulation of transport and to upper (stratospheric) boundary conditions.…”

“…The models involved in TRADEOFF have contributed to numerous previous studies on the impact of aircraft emissions (Penner et al, 1999;Brasseur et al, 1998;Grewe et al, 2001;Meijer et al, 2000;Rogers et al, 2000;Pitari and Mancini, 2001) and participated in previous evaluation studies (Bregman et al, 2001;Law et al, 2000;Rogers et al, 2000;Penner et al, 1999;Brasseur et al, 1998;Houghton et al, 2001). Recently, Law et al (2000) compared monthly mean ozone fields of five CTMs with data from the MOZAIC program, in which ozone is measured continuously from passenger aircraft (Marenco et al, 1998).…”

“…Recently, Law et al (2000) compared monthly mean ozone fields of five CTMs with data from the MOZAIC program, in which ozone is measured continuously from passenger aircraft (Marenco et al, 1998). Another model intercomparison using data from MOZAIC and ozone soundings to evaluate seasonal mean profiles in the lower stratosphere was presented by Bregman et al (2001). Grewe et al (2001) used the extensive data set of NO x observations from the NOXAR project, obtained onboard a Swissair B-747 aircraft over the course of more than one year, to evaluate the NO x distributions calculated by two C-GCMs (E39/C and ULAQ GCM) and to investigate the importance of different sources.…”

Intercomparison of tropospheric ozone models: Ozone transport in a complex tropopause folding event

“…The models generally showed good agreement with observations but often failed to capture sharp ozone concentration gradients in the tropopause region and between extra-tropical and tropical regions. A third intercomparison of ozone models focused on the seasonality of LS ozone and the role of vertical transport [Bregman et al, 2001]. It was found that chemistry-transport models may simulate highly different vertical transport efficiencies in the LS, even when they apply meteorological data from the same source to calculate advection, e.g., from ECMWF analysis.…”

Model evaluation of CO2 and SF6 in the extratropical UT/LS region

“…However, the spatial gradients are small in the UT/LS, which complicate the model evaluation. To overcome this problem, model evaluations were performed with short-lived species (e.g., CO,O 3 , NO x , OH, 14 CO,222 Rn/ 210 PB), which show much stronger spatial gradients [Bregman et al, 2001;Jöckel et al, 2002;Rotman et al, 2004;Brunner et al, 2003Brunner et al, , 2005.…”