Future Arctic ozone recovery: the importance of chemistry and dynamics

Abstract

Abstract. Future trends in Arctic springtime total column ozone, and its chemical and dynamical drivers, are assessed using a seven-member ensemble from the Met Office Unified Model with United Kingdom Chemistry and Aerosols (UM-UKCA) simulating the period 1960-2100. The Arctic mean March total column ozone increases throughout the 21st century at a rate of ∼ 11.5 DU decade −1 , and is projected to return to the 1980 level in the late 2030s. However, the integrations show that even past 2060 springtime Arctic ozone can episodically drop by ∼ 50-100 DU below the corresponding long-term ensemble mean for that period, reaching values characteristic of the near-present-day average level. Consistent with the global decline in inorganic chlorine (Cl y ) over the century, the estimated mean halogeninduced chemical ozone loss in the Arctic lower atmosphere in spring decreases by around a factor of 2 between the periods 2001-2020 and 2061-2080. However, in the presence of a cold and strong polar vortex, elevated halogen-induced ozone losses well above the corresponding long-term mean continue to occur in the simulations into the second part of the century. The ensemble shows a significant cooling trend in the Arctic winter mid-and upper stratosphere, but there is less confidence in the projected temperature trends in the lower stratosphere (100-50 hPa). This is partly due to an increase in downwelling over the Arctic polar cap in winter, which increases transport of ozone into the polar region as well as drives adiabatic warming that partly offsets the radiatively driven stratospheric cooling. However, individual winters characterised by significantly suppressed downwelling, reduced transport and anomalously low temperatures continue to occur in the future. We conclude that, despite the projected long-term recovery of Arctic ozone, the large interannual dynamical variability is expected to continue in the future, thereby facilitating episodic reductions in springtime ozone columns. Whilst our results suggest that the relative role of dynamical processes for determining Arctic springtime ozone will increase in the future, halogen chemistry will remain a smaller but non-negligible contributor for many decades to come.

Deriving Global OH Abundance and Atmospheric Lifetimes for Long‐Lived Gases: A Search for CH3CCl3 Alternatives

“…Model simulation descriptions are included in Text S1 and Table S1 in the supporting information. The six models are divided into two groups according to how tropospheric OH was treated: (i) GEOSCCM (Pawson et al, 2008) and GSFC2D (Fleming et al, 2011) did not include a detailed tropospheric chemistry scheme but prescribed their tropospheric OH with recommended 3-D monthly values from Spivakovsky et al (2000) and (ii) SOCOL (Revell et al, 2015), ULAQ (Pitari et al, 2014), UMUKCA (Bednarz et al, 2016), and WACCM (Garcia et al, 2007) used fully coupled stratosphere-troposphere chemistry schemes, which calculated interactive OH abundance in the troposphere based on surface emissions of NO x , CO, and nonmethane hydrocarbons from the Coupled Model Intercomparison Project Representative Concentration Pathways 4.5 scenario (Lamarque et al, 2011). We also include atmospheric OH abundance and trace gas lifetime estimates from a 12-box Bayesian inversion model (IM) (Rigby et al, 2013).…”

Chemical and dynamical impacts of stratospheric sudden warmings on Arctic ozone variability

“…Bednarz et al . [] found that ozone depletion contributed ~30% to March Arctic ozone variability in a 100 year simulation with the UM‐UKCA chemistry climate model, concluding as we do that dynamical variability is the primary contributor to interannual variations in Arctic spring column O 3 .…”

Review of the global models used within phase 1 of the Chemistry–Climate Model Initiative (CCMI)

“…The chemistry in UMUKCA-UCAM is based on a similar scheme as was used in the UMUKCA models in CCMVal-2 (focusing on the chemistry of stratosphere; Bednarz et al, 2016), but with an explicit treatment of halogen source gases, i.e. no lumping.…”