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 equator
1 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
Near-surface vertical mixing is parametrized partly by a Kraus-Turner mixed layer scheme for tracers Kraus and Turner 1967), and a K-theory scheme(Pacanowski and Philander 1981)for momentum. Below the upper layers the vertical diffusivity is an increasing function of depth only. Convective adjustment is nodified in the region of the Denmark Straits and Iceland-Scotland ridge better to represent down-slope ixing of the overflow water is allowed to find its proper level of neutral buoyancy rather than ixing vertically with surrounding water masses. The scheme is based on Roether et al (1994) Mediterranean water is partially mixed with Atlantic water across the Strait of Gibraltar as a simple representation of water mass exchange since the channel is not resolved in the model The sea ice model uses a simple thermodynamic scheme including leads and snow-cover. Ice is advected by the surface ocean current, with convergence prevented when the depth exceeds 4 m( Cattle and Crossley 1995) There is no explicit representation of iceberg calving, so a prescribed water flux is returned to the ocean at a rate calibrated to balance the net snowfall accumulation on the ice sheets, geographically distributed within regions where icebergs are found. In order to avoid a global average salinity drift, surface water fluxes are converted to surface salinity fluxes using a constant reference salinity of 35 PSU The model is initialized directly from the Levitus et al (1994, 1995)observed ocean state at rest, with a suitable atmospheric and sea ice state. The atmosphere and ocean exchange information once per day. Heat and water fluxes are conserved exactly in the transfer between their different grids References Cattle, H. and J. Crossley, 1995: Modelling Arctic climate change. Phil Trans R Soc London A352 201-213 Cox, P,R Betts, C. Bunton, R. Essery, P.R. Rowntree, and J. Smith, 1999: The impact of new land surface physics on the gCM simulation of climate and climate sensitivity. Climate Dynamics 15: 183-203 climatology on the hadley Centre ccm. uart j, o Meteor. Soc 124 2517-25926. simple aerosol Edwards, J M. and A. Slingo, 1996: Sudies with a flexible new radiation code. I: Choosing a configuration for a large scale model. Quart. J. Roy. Meteor. Soc. 122: 689-719 Gent, P.R. and J C. Mc Williams, 1990: Isopycnal mixing in ocean circulation models. J. Phys. Oceanogr 20:150-155 Gordon, C, C. Cooper, C.A. Senior, H. Banks, J M. Gregory, T.C. Johns, J F B. Mitchell and R.A. Wood 2000: The simulation of SST, sea ice extents and ocean heat transports in a version of the Hadley Centre coupled model without flux adjustments. Climate Dynamics 16: 147-168
2 Near-surface vertical mixing is parametrized partly by a Kraus-Turner mixed layer scheme for tracers (Kraus and Turner 1967), and a K-theory scheme (Pacanowski and Philander 1981) for momentum. Below the upper layers the vertical diffusivity is an increasing function of depth only. Convective adjustment is modified in the region of the Denmark Straits and Iceland-Scotland ridge better to represent down-slope mixing of the overflow water, which is allowed to find its proper level of neutral buoyancy rather than mixing vertically with surrounding water masses. The scheme is based on Roether et al (1994). Mediterranean water is partially mixed with Atlantic water across the Strait of Gibraltar as a simple representation of water mass exchange since the channel is not resolved in the model. The sea ice model uses a simple thermodynamic scheme including leads and snow-cover. Ice is advected by the surface ocean current, with convergence prevented when the depth exceeds 4 m (Cattle and Crossley 1995). There is no explicit representation of iceberg calving, so a prescribed water flux is returned to the ocean at a rate calibrated to balance the net snowfall accumulation on the ice sheets, geographically distributed within regions where icebergs are found. In order to avoid a global average salinity drift, surface water fluxes are converted to surface salinity fluxes using a constant reference salinity of 35 PSU. The model is initialized directly from the Levitus et al (1994, 1995) observed ocean state at rest, with a suitable atmospheric and sea ice state. The atmosphere and ocean exchange information once per day. Heat and water fluxes are conserved exactly in the transfer between their different grids. References: Cattle, H. and J. Crossley, 1995: Modelling Arctic climate change. Phil Trans R Soc London A352: 201-213. Cox, P., R. Betts, C. Bunton, R. Essery, P.R. Rowntree, and J. Smith, 1999: The impact of new land surface physics on the GCM simulation of climate and climate sensitivity. Climate Dynamics 15: 183-203. Cusack S., A. Slingo, J.M. Edwards, and M. Wild, 1998: The radiative impact of a simple aerosol climatology on the Hadley Centre GCM. Quart. J. Roy. Meteor. Soc. 124: 2517-2526. Edwards, J.M. and A. Slingo, 1996: Sudies with a flexible new radiation code. I: Choosing a configuration for a large scale model. Quart. J. Roy. Meteor. Soc. 122: 689-719. Gent, P.R. and J.C. McWilliams, 1990: Isopycnal mixing in ocean circulation models. J. Phys. Oceanogr. 20: 150-155. Gordon, C., C. Cooper, C.A. Senior, H. Banks, J.M. Gregory, T.C. Johns, J.F.B. Mitchell and R.A. Wood, 2000: The simulation of SST, sea ice extents and ocean heat transports in a version of the Hadley Centre coupled model without flux adjustments. Climate Dynamics 16: 147-168
Gregory, D.,R. Kershaw and P.M. Inness, 1997: Parametrization of momentum transport by convection. II tests in single column and general circulation models. Quart. J. Roy. Meteor. Soc. 123: 1153-1183 regory, D, G.J. Shutts and J.R. Mitchell, 1998: A new gravity wave drag scheme incorporating anisotropic orography and low level wave breaking: Impact upon the climate of the UK Meteorological Office Unified Model. Quart. J. Roy. Meteor. Soc. 124: 463-493 Kraus, E B and J.S. Turner, 1967: A one dimensional model of the seasonal thermocline. Part Il. Tellus, 19 98-105 Levitus, S. and TP Boyer, 1994: World Ocean Atlas 1994, Volume 4: Temperature. NOAA/NESDIS E/OC21, US Department of Commerce, Washington, DC, 117pp vitus,S, R Burgett, and T P. Boyer, 1995: World Ocean Atlas 1994, Volume 3: Salinity. NOAA/NESDIS E/OC2l, US Department of Commerce, Washington, DC, 99pp Martin, G.M., D W. Johnson and A. Spice, 1994: The measurement and parametrization of effective radius of droplets in warm stratocumulus clouds. J. Atmos. Sci. 51: 1823-1842 Milton, S.F. and C A. Wilson, 1996: The impact of parametrized sub-grid scale orographic forcing on systematic errors in a global NWP model. Mon. Weath. Rev. 124: 2023-2045 Pacanowski, R.C. and S.G. Philander, 1981: Parametrization of vertical mixing in numerical models of opical oceans. J Phys Oceanogr. 11: 1443-1451 Pope, V.D., M. L. Gallani, P. R. Rowntree and R. A Stratton, 2000: The impact of new physical parametrizations in the Hadley Centre climate model--HadAM3. Climate Dynamics, 16: 123-140 Roether, W.,V.M. Roussenov and R. Well, 1994: A tracer study of the thermohaline circulation of the eastern Mediterranean. In: Ocean Processes in Climate Dynamics: Global and Mediterranean Example pp. 371-394. Eds. P Malanotte-Rizzoli and A R. Robinson, Kluwer Academic Press Smith, R.N. B, 1990: A scheme for predicting layer clouds and their water content in a general circulation model. Quart. J. Roy. Meteor. Soc. 116: 435-460 Visbeck, M.,J. Marshall, T. Haine and M. Spall, 1997: On the specification of eddy transfer coefficients coarse resolution ocean circulation models. J. Phys Oceanogr. 27: 381-402 Wright, D K a new eddy mixing parametrization and ocean general circulation model International WOCE newsl 6:27-29
3 Gregory, D., R. Kershaw and P.M. Inness, 1997: Parametrization of momentum transport by convection. II: tests in single column and general circulation models. Quart. J. Roy. Meteor. Soc. 123: 1153-1183. Gregory, D., G.J. Shutts and J.R. Mitchell, 1998: A new gravity wave drag scheme incorporating anisotropic orography and low level wave breaking: Impact upon the climate of the UK Meteorological Office Unified Model. Quart. J. Roy. Meteor. Soc. 124: 463-493. Kraus, E.B. and J.S. Turner, 1967: A one dimensional model of the seasonal thermocline. Part II. Tellus, 19: 98-105. Levitus, S. and T.P. Boyer, 1994: World Ocean Atlas 1994, Volume 4: Temperature. NOAA/NESDIS E/OC21, US Department of Commerce, Washington, DC, 117pp. Levitus, S., R. Burgett, and T.P. Boyer, 1995: World Ocean Atlas 1994, Volume 3: Salinity. NOAA/NESDIS E/OC21, US Department of Commerce, Washington, DC, 99pp. Martin, G.M., D.W. Johnson and A. Spice, 1994: The measurement and parametrization of effective radius of droplets in warm stratocumulus clouds. J. Atmos. Sci. 51: 1823-1842. Milton, S.F. and C.A.Wilson, 1996: The impact of parametrized sub-grid scale orographic forcing on systematic errors in a global NWP model. Mon. Weath. Rev. 124: 2023-2045. Pacanowski, R.C. and S.G. Philander, 1981: Parametrization of vertical mixing in numerical models of tropical oceans. J. Phys. Oceanogr. 11: 1443-1451. Pope, V. D., M. L. Gallani, P. R. Rowntree and R. A. Stratton, 2000: The impact of new physical parametrizations in the Hadley Centre climate model -- HadAM3. Climate Dynamics, 16: 123-146. Roether, W., V.M. Roussenov and R.Well, 1994: A tracer study of the thermohaline circulation of the eastern Mediterranean. In: Ocean Processes in Climate Dynamics: Global and Mediterranean Example pp.371-394. Eds. P. Malanotte-Rizzoli and A.R. Robinson, Kluwer Academic Press. Smith, R.N.B, 1990: A scheme for predicting layer clouds and their water content in a general circulation model. Quart. J. Roy. Meteor. Soc. 116: 435-460. Visbeck, M., J. Marshall, T. Haine and M. Spall, 1997: On the specification of eddy transfer coefficients in coarse resolution ocean circulation models. J. Phys. Oceanogr. 27: 381-402. Wright, D.K., 1997: A new eddy mixing parametrization and ocean general circulation model. International WOCE newsletter, 26: 27-29
