A new coupled chemistry–climate model for the stratosphere: The importance of coupling for future O<SUB>3</SUB>-climate predictions

Abstract

SUMMARYWe have created a new interactive model for coupled chemistry-climate studies of the stratosphere. The model combines the detailed stratospheric chemistry modules developed and tested in the SLIMCAT/ TOMCAT off-line chemical transport models (CTM) with a version of the Met Office Unified Model (UM). The resulting chemistry-climate model (CCM), called UMCHEM, has a detailed description of stratospheric gasphase and heterogeneous chemistry. The chemical fields of O 3 , N 2 O, CH 4 and H 2 O are used interactively in the radiative heating calculation.We present results from a series of 10-year 'time-slice' experiments for 2000 and 2050 conditions. The UMCHEM model performs well in reproducing basic features of the stratosphere. The distribution of longlived tracers and 'age of air' compare well with observations. For O 3 , the model tends to underestimate the stratospheric column at high latitudes by ∼20 DU. This is due to an underestimate of poleward transport in the mid-low stratosphere. The UMCHEM reproduces well the seasonal cycle in monthly mean column O 3 at midhigh latitudes, though the variability is slightly smaller than observations and smaller than in the SLIMCAT CTM. Other comparisons with the CTM, which has an identical chemistry scheme, show differences resulting from the models' meteorologies. For example, while the CTM reproduces the observed NO y versus N 2 O correlation, the UMCHEM overestimates the slope by about a factor of 2.Including full chemistry in the UM causes important differences in the model's meteorology. As the zonal mean ozone climatology used in the UM is larger than that calculated in UMCHEM, with a maximum difference of 4 ppmv in the upper stratosphere, the UMCHEM temperature is about 4 K lower in the Antarctic lower stratosphere and 1-6 K higher in the upper stratosphere. The age of air is less in the basic UM by about 1-3 months in the lower stratosphere but slightly greater in the upper stratosphere. Coupling of the more realistic stratospheric chemistry water vapour warms the model stratosphere by ∼1-2 K. This water vapour coupling also results in a decrease in ozone with a maximum difference of about 250 ppbv in the tropical and southern highlatitude upper stratosphere, while in the tropical lower stratosphere ozone concentrations are increased by up to 30 ppbv.For 2050 conditions, the model produces a column O 3 5% higher than present-day values in the tropics, about 15% higher in the Arctic winter/spring and up to 90% higher in the much smaller Antarctic O 3 hole. This large O 3 increase more than offsets the effect of cooling in the Antarctic late spring induced by greenhouse gases.

Interactions of meteoric smoke particles with sulphuric acid in the Earth's stratosphere

“…UMSLIMCAT is based on the UK Met Office Unified Model (UM) with a stratospheric chemistry scheme from the SLIMCAT model (Chipperfield, 2006). The CCM is described in detail elsewhere (Tian and Chipperfield, 2005). Briefly, the model has 64 vertical levels from the surface to 0.01 hPa (∼80 km) and a horizontal resolution of 2.5 • ×3.75 • .…”

Representation of tropical deep convection in atmospheric models – Part 2: Tracer transport

“…UMSLIMCAT is a coupled chemistry-climate model based on the extended middle atmosphere version of UM version 4.5 (Tian and Chipperfield, 2005). Like UMCAM, the horizontal resolution is 2.5 • latitude × 3.75 • longitude but the model has 64 vertical levels between the surface and 0.01 hPa.…”

Influence of the Arctic Oscillation on the Vertical Distribution of Wintertime Ozone in the Stratosphere and Upper Troposphere over the Northern Hemisphere

“…However, interpretation of long-term ozone variation is difficult since the ozone field exhibits not only a complicated trend, forced by changes in ozone-depleting substances superimposed on a changing climate, but also interannual variability related to various meteorological conditions (e.g., Weiss et al 2001;Hadjinicolaou et al 2002;Tian and Chipperfield 2005;Austin et al 2010;Eyring et al 2010;Liu et al 2013;Douglass et al 2014). The World Meteorological Organization (WMO 2007(WMO , 2011 highlighted the fact that meteorology can also significantly influence the long-term trend of total ozone column (TOC); in particular, meteorological variability can explain as much as 20%-50% of TOC variability in the extratropics of the Northern Hemisphere during winter and spring.…”