A multi-model analysis of the role of the ocean on the African and Asian monsoon during the mid-Holocene

We investigate the role of the ocean feedback on the climate response to insolation forcing during the mid-Holocene (6000 yr B.P.) using results from seven coupled ocean-atmosphere general circulation models. This leads us to consider how the late summer sea
surface temperature (SST) anomalies dipole in the tropical Atlantic increases the length of the African monsoon, how this dipole like structure is created and maintained, and how the late summer SST warming in the northwest Indian ocean impacts the monsoon retreat in this sector. Even though the coupled models we consider do not accurately
represent all the characteristics of modern climate in the tropics, several robust mechanisms are found. They involve a strong wind evaporation feedback and changes in the mixed layer depth that enhance the insolation forcing, as well as increased Ekman
transport in the Atlantic that contributed to sharpen the Atlantic dipole like pattern. We also consider changes in interannual variability over Sahara West Africa and the Indian Ocean. It is found that teleconnection between variations in SST and Sahel precipitation are in favor of a larger impact of the Atlantic dipole mode in this region. In
the Indian Ocean, the strengthening of the Indian dipole likestructure in autumn has a damping effect on the Indian dipole mode at the interannual time scale. These analysis represent preliminary investigations that will continue using more complete simulations within the second phase of the Paleoclimate Modeling Intercomparison Project (PMIP).