Mesoscale Signature of the North Atlantic Oscillation and Its Interaction With the Ocean

This observational study uses high‐resolution data to investigate mesoscale signatures of the North Atlantic Oscillation (NAO) in the atmosphere and ocean. The production of spatially high‐pass (“mesoscale”) filtered kinetic energy by buoyancy and shear effects in the atmosphere, along with sea surface temperature and surface currents in the ocean is described, and a difference with NAO phase is found. In positive NAO winters, an extension of the Gulf Stream warm core is observed, along with a displacement and acceleration of surface currents. Mesoscale activity in the atmosphere appears to follow this extension of the warm core of the Gulf Stream. This, we suggest, is a new feature of NAO air‐sea interactions which is embedded within the basin‐scale NAO patterns discussed previously in the literature. Further downstream, mesoscale activity seems to reflect more passively the general poleward migration of synoptic activity in positive NAO conditions. Robust atmospheric mesoscale signals are embedded within basin‐scale NAO variability in the western North AtlanticThis mesoscale variability might be a response to changes in the temperature and velocity structure of the Gulf Stream driven by the NAOStudy examines the new high‐resolution ERA5 atmospheric reanalysis