A Lagrangian analysis of midlatitude air-sea interaction associated with mesoscale oceanic eddies

Air-sea interaction in the middle latitudes is scale-dependent. At horizontal scales of 100 km or larger, which is the typical grid-size for global climate models, atmospheric forcing of oceanic variability tends to dominate at the air-sea interface. At smaller spatial scales, the forcing of the atmosphere by oceanic eddies becomes the dominant signal at the air-sea interface. This scale dependence is evident in the correlation between sea surface temperature (SST) and surface wind speed, which tends to be negative at larger spatial scales, because strong atmospheric winds tend to cool the ocean, and positive at smaller spatial scales, as the oceanic eddies alter the atmospheric boundary layer.

In this study, we carry out a Lagrangian analysis of the atmospheric response to mesoscale eddies in the Gulf Stream region of the North Atlantic. An objective eddy-recognition algorithm based on sea surface height data is used to identify oceanic features in eddy-resolving coupled simulations carried out using both the NCAR CESM and a coupling of WRF-ARW with ROMS. The atmospheric state overlying the cyclonic and anticyclonic ocean eddies is composited separately to assess the impact of the different SST anomalies on the atmospheric boundary layer. Our analysis shows that anticyclonic eddies have a clear atmospheric signature, with warmer SST associated with increased precipitation, stronger surface winds, and greater boundary layer heights. Cyclonic eddies show the opposite pattern compared to a weighted mean.