Representation of the Atlantic Meridional Mode By Climate Models: Influence of Mean Biases and Feedback Processes

The Atlantic Meridional Mode (AMM) is investigated in a set of coupled simulations performed by a sub-ensemble of CMIP5 models. The SST and wind anomalies associated with the AMM are captured reasonably well by models, though the amplitude of the SST inter-hemispheric gradient is clearly underestimated by models. 

The representation the WES (Wind-evaporation-SST) feedback mechanism, key process to create the inter-hemispheric SST variability, is also investigated in models and several observational datasets. Results show that some parts of the WES feedback are well reproduced by models. However, SSTs in models seem to over-react to latent flux anomalies, comparing to observational datasets.

In the last part of the work, links between SST mean errors and AMM are investigated in the Tropical Atlantic. As SST mean biases are very similar amongst CMIP5 models, these links are very difficult to assess. For this reason, a anomaly coupling experimental protocol has been implemented on only one CMIP5 model. The results of some idealized experiments in which climatology of solar heat flux and wind stress are constraint to the observed state are presented and discussed.