HadCM3--Coupled atmosphere-Ocean general circulation model HadCM3 is a coupled atmosphere-ocean general circulation model (AOGCM) developed at the Hadley Centre and described by gordon et al (2000) and Pope et al(2000). Unlike earlier AOGCMs at the Hadley Centre and elsewhere(including HadCM2), HadCM3 does not need flux adjustment(additional"artificial heat and freshwater fluxes at the ocean surface)to produce a good simulation. The higher ocean resolution of HadCM3 is a major factor in this. HadCM3 has been run for over a thousand years, showing little drift in ts surface climate The atmospheric component of HadCM3 has 19 levels with a horizontal resolution of 2.5 of latitude 3.75 of longitude, which produces a global grid of 96x 73 grid cells. This is equivalent to a surfa resolution of about 417 km x 278 km at the Equator, reducing to 295 km x 278 km at 45 of latitude (comparable to a spectral resolution of T42) A new radiation scheme is included with 6 and 8 spectral bands in the solar(shortwave) and terrestrial thermal (longwave) wavelengths. The radiative effects of minor greenhouse gases as well as CO2, water vapour and ozone are explicitly represented(Edwards and Slingo, 1996). A simple parametrization of background aerosol( Cusack et al 1998)is also included A new land surface scheme(Cox et al 1999)includes a representation of the freezing and melting of soil moisture, as well as surface runoff and soil drainage, the formulation of evaporation includes the dependence of stomatal resistance on temperature, vapour pressure and CO2 concentration. The surface bedo is a function of snow depth, vegetation type and also of temperature over snow and ice A penetrative convective scheme( Gregory and Rowntree, 1990) is used, modified to include an explicit down-draught, and the direct impact of convection on momentum( Gregory et al 1997). Parametrizations of orographic and gravity wave drag have been revised to model the effects of anisotropic orography, high drag states, flow blocking and trapped lee waves(Milton and Wilson 1996: Gregory et al 1998). The large-scale precipitation and cloud scheme is formulated in terms of an explicit cloud water variable following Smith(1990). The effective radius of cloud droplets is a function of cloud water content and droplet number concentration( Martin et al 1994) The atmospheric component of the model also optionally allows the emission, transport, oxidation and deposition of sulphur compounds(dimethylsulphide, sulphur dioxide and ammonium sulphate) to be simulated interactively. This permits the direct and indirect forcing effects of sulphate aerosols to be modelled given scenarios for sulphur emissions and oxidants The oceanic component of HadCM3 has 20 levels with a horizontal resolution of 1.25 x 1.25. At this resolution it is possible to represent important details in oceanic current structures Horizontal mixing of tracers uses a version of the Gent and Mc Williams(1990) adiabatic diffusion scheme with a variable thickness diffusivity(Wright 1997, Visbeck et al. 1997) is used. There is no explicit horizontal diffusion of tracers. The along-isopycnal diffusivity of tracers is 1000 m2 S-l and horizontal omentum viscosity varies with latitude between 3000 and 6000 m2 S-1 at the poles and equator1 HadCM3--Coupled atmosphere - Ocean general circulation model HadCM3 is a coupled atmosphere-ocean general circulation model (AOGCM) developed at the Hadley Centre and described by Gordon et al (2000) and Pope et al (2000). Unlike earlier AOGCMs at the Hadley Centre and elsewhere (including HadCM2), HadCM3 does not need flux adjustment (additional "artificial" heat and freshwater fluxes at the ocean surface) to produce a good simulation. The higher ocean resolution of HadCM3 is a major factor in this. HadCM3 has been run for over a thousand years, showing little drift in its surface climate. The atmospheric component of HadCM3 has 19 levels with a horizontal resolution of 2.5° of latitude by 3.75° of longitude, which produces a global grid of 96 x 73 grid cells. This is equivalent to a surface resolution of about 417 km x 278 km at the Equator, reducing to 295 km x 278 km at 45° of latitude (comparable to a spectral resolution of T42). A new radiation scheme is included with 6 and 8 spectral bands in the solar (shortwave) and terrestrial thermal (longwave) wavelengths. The radiative effects of minor greenhouse gases as well as CO2, water vapour and ozone are explicitly represented (Edwards and Slingo, 1996). A simple parametrization of background aerosol (Cusack et al 1998) is also included. A new land surface scheme (Cox et al 1999) includes a representation of the freezing and melting of soil moisture, as well as surface runoff and soil drainage; the formulation of evaporation includes the dependence of stomatal resistance on temperature, vapour pressure and CO2 concentration. The surface albedo is a function of snow depth, vegetation type and also of temperature over snow and ice. A penetrative convective scheme (Gregory and Rowntree, 1990) is used, modified to include an explicit down-draught, and the direct impact of convection on momentum (Gregory et al 1997). Parametrizations of orographic and gravity wave drag have been revised to model the effects of anisotropic orography, high drag states, flow blocking and trapped lee waves (Milton and Wilson 1996; Gregory et al 1998). The large-scale precipitation and cloud scheme is formulated in terms of an explicit cloud water variable following Smith (1990). The effective radius of cloud droplets is a function of cloud water content and droplet number concentration (Martin et al 1994). The atmospheric component of the model also optionally allows the emission, transport, oxidation and deposition of sulphur compounds (dimethylsulphide, sulphur dioxide and ammonium sulphate) to be simulated interactively. This permits the direct and indirect forcing effects of sulphate aerosols to be modelled given scenarios for sulphur emissions and oxidants. The oceanic component of HadCM3 has 20 levels with a horizontal resolution of 1.25 x 1.25°. At this resolution it is possible to represent important details in oceanic current structures. Horizontal mixing of tracers uses a version of the Gent and McWilliams (1990) adiabatic diffusion scheme with a variable thickness diffusivity (Wright 1997; Visbeck et al. 1997) is used. There is no explicit horizontal diffusion of tracers. The along-isopycnal diffusivity of tracers is 1000 m2 s-1 and horizontal momentum viscosity varies with latitude between 3000 and 6000 m2 s-1 at the poles and equator respectively