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

Abstract

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.

Simulating the Midlatitude Atmospheric Circulation: What Might We Gain From High-Resolution Modeling of Air-Sea Interactions?

“…The impact of warmer SST anomalies north of the separated Gulf Stream on the strength of the Icelandic Low, although with a different sign, was highlighted in earlier studies of decadal variability in the Atlantic in long instrumental records (e.g., [124,125]) 9 . The dynamics is certainly complex, as studies using high-resolution reanalysis dataset (ERA5, with 25 km resolution) have emphasized the presence of tropospheric mesoscale signals set by the Gulf Stream warm core [127], in addition to the non-linear effects suggested in some LAM studies (e.g., [65], see the BComparison With the Simulated Response of AGCMs to Prescribed Extra-Tropical SST Anomalies^section).…”

Oceanic maintenance of atmospheric blocking in wintertime in the North Atlantic

“…Once the supply of negative or low PV air mass has been cut off, the block begins to decay. This negative feedback process is also seen in Cobb and Czaja (2019) in which the reduction (extension) of the warm core of the Gulf Stream, as a result of consecutive negative (positive) NAO periods, resulted in less (more) negative PV air masses occurring in the atmospheric boundary layer of this region. The timescale of this negative feedback driven by air-sea interactions in our study is about 3 months.…”