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Model description

One of the possible way to identify what part of the observed ozone trend can be explained by the changes in the concentrations of CFCs is to apply a 3-D Atmospheric Chemical-Transport model (ACTM) driven by assimilated circulation fields which supposed to be very close to the real meteorological situation. Such temperature and wind fields are available from the UKMO assimilation data set (Swinbank, 1994) since 1991, and it has been proven by Chipperfield (1999) that the total ozone distribution can be successfully simulated with a state-of-the-art ACTM driven by these winds.

We have estimated the contribution of Montreal Protocol and its Amendments to the modern ozone trends using the UIUC 24-layer Stratospheric Chemical Transport model (UIUC SCTM) (Rozanov et al., 1999a) driven by UKMO assimilated wind and temperature fields for the period 1993-2000. The UIUC SCTM is a global grid-point 24 level model with horizontal resolution of 40° by latitude and 50° by longitude. In the vertical direction the model extends from the Earth's surface to 1 hPa. The chemical part of the model has been updated by including the methane oxidation chain and bromine cycle which were not accounted for in the basic version (Rozanov et al., 1999a). The initial conditions for the trace gas concentrations have been taken from UARS climatological data for August 1992 (http://hyperion.gsfc.nasa.gov/Analysis/UARS/urap/home.html). The Pinatubo aerosol properties have been adopted from Stenchikov et al. (1998). The ground level concentrations of CO2, CH4, N2O, CFC-11 and CFC-12 for each simulated year have been taken from NOAA/CMDL database (http://www.cmdl.noaa.gov/hats/index.html), separately for the Northern and Southern hemispheres as a seasonal data. The surface mixing ratio of CFCs have been scaled to take into account the other sources of active chlorine. The surface fluxes of NOx and CO have been acquired from Müller et al. (1995). The same database has been used for the prescribing of NOx lightning source.