HadCM3 Thermohaline Circulation 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. The Thermohaline Circulation (THC) simulation output contained in this dataset was used to investigate the response of the Atlantic THC and the climate to increased freshwater fluxes of 0.1 Sv (1 Sv=10**6 m**3 s*-1) and 1.0 Sv for a period of 100 years. The increased freshwater fluxes were then stopped to determine if the decline in THC would reverse. All other forcing and bounday conditions were as for the hadCM3 control simulation. 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).