A positive atmospheric feedback on the North Atlantic warming hole.

A persistent cooling trend in the subpolar North Atlantic known as the North Atlantic Warming Hole (NAWH) has appeared in sea surface temperature (SST) observations since 1870, and the reasons for its persistence in an era of rapid anthropogenic global warming remain elusive. Here we investigate the response of the atmosphere to the NAWH in a set of model experiments, and further examine the associated feedback mechanisms. In one experiment, the observed warming hole is imposed upon the present-day climatology, and in another we run a sensitivity experiment, shifting the location of the warming hole southward of its observed location to limit its direct interaction with the jet stream. Surprisingly, the response of the jet stream and surface circulation is relatively insensitive to the latitude of the NAWH within the basin. However, the capacity for the atmospheric response to invoke a positive feedback onto the SST forcing does depend on proximity to the midlatitude jet stream. These results distinctly differ from similar coarser resolution experiments but align with observed patterns, highlighting the importance of eddies in determining the response of the midlatitude atmosphere to persistent SST forcing. These findings therefore augment our understanding of the long-term persistence of the NAWH.