Abstract
Canonical understanding based on general circulation models (GCMs) is that the atmospheric circulation response to midlatitude sea‐surface temperature (SST) anomalies is weak compared to the larger influence of tropical SST anomalies. However, the ∼100‐km horizontal resolution of modern GCMs is too coarse to resolve strong updrafts within weather fronts, which could provide a pathway for surface anomalies to be communicated aloft. We utilize variable-resolution capabilities within the CESM2 global climate model to investigate the influence of increased resolution over the North Atlantic, from a typical ~100-km resolution up to a 14-km resolution that better resolves weather fronts, on large-scale atmosphere-ocean coupling. The highest resolution simulations show a large positive response of the wintertime North Atlantic Oscillation (NAO) to specified positive SST anomalies in the Gulf Stream, including those that occur as part of a tripole pattern in response to prior NAO forcing. The lower‐resolution simulations show a weaker response with a different spatial structure. The enhanced large‐scale circulation response at higher resolution results from an increase in resolved vertical motions at the mesoscale and the associated increase in vertical eddy heat and momentum transport in the free troposphere. Our results imply that conventional coarse-resolution climate models underestimate the positive feedback of midlatitude North Atlantic SSTs on the NAO and that increased model resolution offers a pathway towards improved prediction on seasonal-to-decadal timescales.