Mellado-Cano, J., Barriopedro, D., García-Herrera, R., Trigo, R. M., & Hernández, A. (2019). Examining the North Atlantic Oscillation, East Atlantic pattern and jet variability since 1685. Journal of Climate. https://doi.org/10.1175/JCLI-D-19-0135.1
Recent studies have stressed the key role of the East Atlantic (EA) pattern and its interactions with the North Atlantic Oscillation (NAO) in Euro-Atlantic climate variability. However, instrumental records of these leading patterns of variability are short, hampering a proper characterization of the atmospheric circulation beyond the mid-19th century. In this work, we present the longest (1685-2014) observational-based records of winter NAO and EA indices as well as estimates of the North Atlantic eddy-driven jet stream speed and latitude for the same period. The time series display large variability from interannual to multidecadal time scales, with e.g. positive (negative) EA (NAO) phases dominating before 1750 (during much of the 19th century). By identifying winters with different combinations of NAO/EA phases in the 20th century, our results highlight the additional role of EA in shaping the North Atlantic action centers and the European climate responses to NAO. The EA interference with the NAO signal is stronger in precipitation than in temperature and affects areas with strong responses to NAO such as Greenland and the western Mediterranean, which prevents against simplistic relationships of natural proxies with NAO. The last three centuries uncover multidecadal periods dominated by specific NAO/EA states and substantial interannual to centennial variability in the North Atlantic jet stream, thus providing new evidences of the dynamics behind some outstanding periods. Transitions in the NAO/EA phase space have been recurrent and pin down long-lasting anomalies, such as the displacement of the North Atlantic action centers in the late 20th century, besides some disagreements between NAO indices.