HadCM3 Separable Fluxes Model Intercomparison Experiment

The Hadley Centre Coupled Model Version 3 was developed from the earlier HadCM2 model. Various improvements were applied to the 19 level atmosphere model and the 20 level ocean model and as a result the model requires no artificial flux adjustments to prevent excessive climate drift. The atmosphere and ocean exchange information once per day, heat and water fluxes being conserved exactly. Momentum fluxes are interpolated between atmosphere and ocean grids so are not conserved precisely, but this non-conservation is not thought to have a significant effect. The main differences from the previous HadCM2 model are a significantly more sophisticated radiation scheme; the inclusion of the direct impact of convection on momentum; and the inclusion of a new land surface scheme that includes a better representation of evaporation, freezing and melting of soil moisture. This model experiment was performed to compare the response of the Atlantic thermohaline circulation (THC) to time-dependent climate change caused by increasing atmospheric CO2 concentration. It partners the HadCM3-THCMIP simulation but the focus in this case was to investigate the relative impact of surface water fluxes and surface heat fluxes on THC. It comprises several simulations all of a 140 year duration which can be compared with the HadCM3 control experiment. The simulation runs used a variety of combinations of 1% compound growth in CO2 and daily water fluxes (control and a 1% increase) as described in Gregory et al. (2005). These simulation data were intercompared with equivalent outputs from other climate models as an activity of the World Climate Research program (WCRP) Coupled Model InterComparison Project (CMIP). -->