Quantitative assessment of Southern Hemisphere ozone in chemistry-climate model simulations

Abstract

Abstract. Stratospheric ozone recovery in the SouthernHemisphere is expected to drive pronounced trends in atmospheric temperature and circulation from the stratosphere to the troposphere in the 21st century; therefore ozone changes need to be accounted for in future climate simulations. Many climate models do not have interactive ozone chemistry and rely on prescribed ozone fields, which may be obtained from coupled chemistry-climate model (CCM) simulations. However CCMs vary widely in their predictions of ozone evolution, complicating the selection of ozone boundary conditions for future climate simulations. In order to assess which models might be expected to better simulate future ozone evolution, and thus provide more realistic ozone boundary conditions, we assess the ability of twelve CCMs to simulate observed ozone climatology and trends and rank the models according to their errors averaged across the individual diagnostics chosen. According to our analysis no one model performs better than the others in all the diagnostics; however, combining errors in individual diagnostics into one metric of model performance allows us to objectively rank the models. The multi-model average shows better overall agreement with the observations than any individual model. Based on this analysis we conclude that the multi-model average ozone projection presents the best estimate of future ozone evolution and recommend it for use as a boundary condition in future climate simulations. Our results also demonstrate a sensitivity of the analysis to the choice of reference data set Correspondence to: A. Yu. Karpechko (alexey.karpechko@fmi.fi) for vertical ozone distribution over the Antarctic, highlighting the constraints that large observational uncertainty imposes on such model verification.

Middle atmosphere response to the solar cycle in irradiance and ionizing particle precipitation

“…This is reflected in the SH stratosphere temperature field where the warm anomaly in middle and high latitudes disappears in the presence of EPP (Fig. 19, top right vs. bottom right), in better agreement with observations (Keckhut et al, 2005). The polar ozone buildup with increasing solar activity in the absence of EPP modifies the evolution of the polar vortex during the initial stages of its development so as to make it weaker around 60 • S by reducing the meridional temperature gradient.…”

“…Given that the model ozone in the troposphere is within 10 % of observations any radiative impact on the dynamics and transport is limited. This is borne out by the reasonable climate and sensitivity of the model (Eyring et al, 2006;Karpechko et al, 2010). Neither the lack of wet removal nor additional air quality chemistry in the model should change the fact that GCR leads to a net increase of tropospheric NO y and ozone.…”

Quantitative evaluation of ozone and selected climate parameters in a set of EMAC simulations

“…The weights w ij k are proportional to the area of the (i, j ) gridbox and to the length of each month k. The weight are normalized by their sum W . This metric has been considered (among others) by Taylor (2001), Jöckel et al (2006), Gleckler et al (2008), Reichler and Kim (2008), Karpechko et al (2010) and Yokoi et al (2011). While Taylor (2001) and Yokoi et al (2011) did not consider any weighting, Gleckler et al (2008), Reichler and Kim (2008) and Karpechko et al (2010) use the weighting described above.…”

“…This metric has been considered (among others) by Taylor (2001), Jöckel et al (2006), Gleckler et al (2008), Reichler and Kim (2008), Karpechko et al (2010) and Yokoi et al (2011). While Taylor (2001) and Yokoi et al (2011) did not consider any weighting, Gleckler et al (2008), Reichler and Kim (2008) and Karpechko et al (2010) use the weighting described above. Additionally, Reichler and Kim (2008) weighted the sum also by a factor indirectly proportional to the variance from the observation (thus stressing the variables with lower variance), and Karpechko et al (2010) by a factor indirectly proportional to the uncertainty in the observed variable (thus laying stress on more accurate observations).…”

Attribution of observed changes in stratospheric ozone and temperature

“…The projections of future ozone evolution contained in the recent WMO Ozone Assessment (WMO, 2011) rely heavily on three-dimensional chemistry-climate models, and on the realism of their simulated ozone response to greenhouse changes. However, while historical trends in total column ozone simulated in response to combined ODS and greenhouse gas forcings have been shown to be reasonably consistent with observations, (Chapter 3 of SPARC CCMVal, 2010; Karpechko et al, 2010), the simulated stratospheric temperature and ozone response to greenhouse gases in these models has not previously been directly tested against observations. ODSs have been the dominant driver of past stratospheric ozone changes, and ozone changes have been the dominant driver of lower stratospheric temperature changes (WMO, 1999;Shine et al, 2003;Santer et al, 2003;Cordero and Forster, 2006;Ramaswamy et al, 2006).…”