Previous: Ext. Abst. Next: Experiment design Up: Ext. Abst.

1. Model description

MA-ECHAM/CHEM is a spectral General Circulation Model with interactive chemistry from surface to a height of about 80 Km, based on the 'Middle Atmosphere version of the European Centre model in HAMburg' (Roeckner et al, 1996). The horizontal resolution is T30, with 39 vertical layers (top at 0.01 hPa) and time step set to 15 minutes. The model incorporates the parameterisation of gravity wave effects from Manzini and McFarlane (1998) and uses the Spitfire advection scheme.

The chemistry module CHEM (Steil et al, 1998) contains chemical processes required to describe stratospheric ozone chemistry and tropospheric background chemistry. 18 species are transported individually or as families, and diagnostic methane oxidation is calculated. 110 photochemical reactions are taken into account, and the photolysis rates are calculated 'on-line' using the accurate and computationally effective scheme of Landgraf and Crutzen (1998) which also includes changes in clouds and ozone. The concentration of the long lived species is prescribed at the surface, while for the short lived species their emissions and dry deposition are prescribed also at the surface. At the top, only the NOx concentration is prescribed using observations from UARS/HALOE, varying with latitude, height and season. Heterogeneous reactions on Polar Stratospheric Clouds (PSCs) of type I and II and on sulphate aerosol are included. The model is fully interactive, i.e. changes in chemistry have a feedback into dynamics through their influence on radiation.