To gain insight into the atmospheric teleconnections associated with the AMV, we perform idealized experiments using Community Earth System Model version 1 (CESM1) in which North Atlantic SSTs are restored to a time-independent spatial pattern corresponding to an estimate of the internal component of the observed AMV anomaly (see Ruprich-Robert et al. (2017) for more details). CESM1 uses nominal 1˚ horizontal resolution in all its components. Because we aim to assess the effects of internal variability, all experiments use pre-industrial conditions where external forcings are kept fixed at levels corresponding to either calendar year 1850. The restoring is fully applied between 8°−65°N in the North Atlantic, linearly diminishing to zero within 8° buffer zones at the northern and southern boundaries, so that the constrained region is confined between the Equator and 73°N. Outside of this region, the models evolve freely, allowing a full response of the climate system to the AMV–related SST anomalies. To obtain reliable estimates of the AMV impacts, we perform large ensemble simulations with 30 members. SST anomalies corresponding to one standard deviation of the AMV index are added to or subtracted from the models daily climatological SST over the North Atlantic region for the positive (AMV+) or negative (AMV-) AMV experiments, respectively. The restoring time scale is 5 days over 10 m.
