The impact of Atlantic and Pacific Ocean sea surface temperature anomalies on the North Atlantic multidecadal variability

Globally forced model simulations with an atmospheric general circulation model of intermediate complexity reveal surface air temperature (SAT) and sea level pressure (SLP) variations at multidecadal time scales. In order to separate the influence of individual ocean basins on the North Atlantic multidecadal variability, we force our model with observed SST data for the period 1856-2000 for Atlantic and Pacific Oceans, separately, while outside the atmosphere is coupled with the ocean via a mixed layer slab model. The experiments indicate the Atlantic Ocean as a principal driver of North Atlantic multidecadal variability, with SAT and SLP highly in phase in the North Atlantic at about 60-70 yr time scale. The Pacific impact is associated to longer period variations in the SLP field over the North Atlantic. We suggest that two distinct physical modes of multidecadal climate variability exist, one of about 70 yr possibly linked with the Atlantic thermohaline circulation, the other linked with the Pacific Ocean and connected to the Atlantic Ocean via Pacific-North America teleconnections. The latter has a time scale of about 80-100 yr.