Amendments to FAFMIP experimental design agreed in April 2019

At our meeting in April 2019, we decided to add three experiments:

• faf-heat-NA50pct experiment in Tier 1. This experiment has exactly the same design as the faf-heat experiment, except that within part of the North Atlantic ocean the heat flux perturbation is multiplied by 0.5. It has been carried out with several AOGCMs and it produces an AMOC weakening that is similar to that in 1pctCO2, whereas the original faf-heat experiment gives a greater weakening because of the redistribution feedback. We will retain the original faf-heat experiment in tier 1 as well.
• faf-heat-NA0pct experiment in Tier 2. This is like faf-heat-NA50pct, with zero perturbation in the North Atlantic region.
• faf-antwater-stress experiment in Tier 2, at the request of the Southern Ocean Model Intercomparison Project (SOMIP). This experiment simultaneously applies the momentum flux perturbation, as in faf-stress, and a freshwater flux of 0.1 Sv in total to be applied uniformly around the coast of Antarctica, in whatever way is most suitable in the model.

We agreed also that it would be useful to add passive heat, using the surface flux of the faf-heat and faf-passiveheat experiments, in the faf-stress and faf-water experiments. Passive heat has no effect on the evolution (because it's passive!), but would give us information about the effect of the other surface fluxes on passive heat uptake processes. These effects are probably relevant to the heat uptake which occurs in faf-heat or in a conventional AOGCM CO2-forced experiment, in which all the surface fluxes are perturbed.