Abstract
Abstract. Recent observational and modeling studies suggest that stratospheric ozone depletion not only influences the surface climate in the Southern Hemisphere (SH), but also impacts Northern Hemisphere (NH) spring, which implies a strong interaction between dynamics and chemistry. Here, we systematically analyze the importance of interactive chemistry with respect to the representation of stratosphere–troposphere coupling and in particular the effects on NH surface climate during the recent past. We use the interactive and specified chemistry version of NCAR's Whole Atmosphere Community Climate Model coupled to an ocean model to investigate differences in the mean state of the NH stratosphere as well as in stratospheric extreme events, namely sudden stratospheric warmings (SSWs), and their surface impacts. To be able to focus on differences that arise from two-way interactions between chemistry and dynamics in the model, the specified chemistry model version uses a time-evolving, model-consistent ozone field generated by the interactive chemistry model version. We also test the effects of zonally symmetric versus asymmetric prescribed ozone, evaluating the importance of ozone waves in the representation of stratospheric mean state and variability. The interactive chemistry simulation is characterized by a significantly stronger and colder polar night jet (PNJ) during spring when ozone depletion becomes important. We identify a negative feedback between lower stratospheric ozone and atmospheric dynamics during the breakdown of the stratospheric polar vortex in the NH, which contributes to the different characteristics of the PNJ between the simulations. Not only the mean state, but also stratospheric variability is better represented in the interactive chemistry simulation, which shows a more realistic distribution of SSWs as well as a more persistent surface impact afterwards compared with the simulation where the feedback between chemistry and dynamics is switched off. We hypothesize that this is also related to the feedback between ozone and dynamics via the intrusion of ozone-rich air into polar latitudes during SSWs. The results from the zonally asymmetric ozone simulation are closer to the interactive chemistry simulations, implying that under a model-consistent ozone forcing, a three-dimensional (3-D) representation of the prescribed ozone field is desirable. This suggests that a 3-D ozone forcing, as recommended for the upcoming CMIP6 simulations, has the potential to improve the representation of stratospheric dynamics and chemistry. Our findings underline the importance of the representation of interactive chemistry and its feedback on the stratospheric mean state and variability not only in the SH but also in the NH during the recent past.
Highlights
Ozone is a key constituent of the stratosphere and is important for stratospheric chemistry, and for transport and dynamics
We identify a negative feedback between lower stratospheric ozone and atmospheric dynamics during the breakdown of the stratospheric polar vortex in the Northern Hemisphere (NH), which contributes to the different characteristics of the polar night jet (PNJ) between the simulations
In this study we systematically investigated the effect of interactive chemistry on the characteristics of the stratospheric polar vortex in CESM1(WACCM) during the second half of the 20th century and the beginning of the 21st century with a focus on the NH climatology as well as on its interannual variability
Summary
Ozone is a key constituent of the stratosphere and is important for stratospheric chemistry, and for transport and dynamics. Depending on the strength of the PNJ, upward planetary wave propagation and dissipation can either be enhanced or diminished (Charney and Drazin, 1961) This has opposing effects on the state of the polar vortex and can lead to either positive or negative feedbacks between ozone depletion and stratospheric dynamics (B and C in Fig. 1) (e.g., Mahlman et al, 1994; Manzini et al, 2003; Lin et al, 2017). Gillett et al (2009), for example, showed that the NH polar stratospheric vortex is warmer when using zonally asymmetric ozone compared with zonal mean ozone in the radiation scheme In their model setup feedbacks between dynamics and zonal mean ozone concentrations were possible, only the effects of ozone waves were inhibited. We conclude the paper with a discussion of our results
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