Simulated and observed atmospheric response to oceanic mesoscale eddies in the Gulf Stream region

The availability of high-resolution satellite measurements has highlighted the role of the impact of oceanic mesoscale eddies in midlatitude air-sea interaction. The observational data clearly identify near-surface aspects of this interaction, such as the positive correlation at smaller spatial scales between sea surface temperature (SST) anomalies and surface wind speed. The question of how deep the impact of oceanic eddies penetrates into the troposphere remains an open question. Satellite observations cannot really address this question and it is not clear if atmospheric reanalysis have adequate horizontal resolution to fully resolve the impact of oceanic eddies.

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 is used to identify oceanic features in high-resolution global and regional coupled model simulations as well as atmospheric reanalyses. Composite analysis is used to assess the vertical structure of the atmospheric response to oceanic mesoscale eddies. Consistent with other studies, our results show that anticyclonic eddies increase surface winds, cloud cover, and rainfall rates, with cyclonic eddies having an opposing effect. The vertical momentum mixing mechanism is evident as the primary driver of the surface wind response to SST anomalies. This vertical mixing causes the strongest atmospheric response to occur slightly downstream of the eddy center. Clouds, rainfall, and vertical motion also exhibit a downstream response in the model simulations. Low-level clouds form beyond the boundary layer up to 800 hPa, with increased vertical motion seen up to the 600 hPa level. Atmospheric reanalyses are indeed able to capture some aspects of the response to oceanic eddies.