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Abstract:
The Eddy Driven Jet (EDJ) is a major driver of extreme weather events occurring in the mid-latitudes in the Northern Hemisphere. A ubiquitous approach to quantifying the variability of the North Atlantic EDJ, is to locate the position of the maximum zonal wind over the North Atlantic sector. This identifies three ‘regimes’ of the jet representing a Southern, Northern and Central jet position.However, the process of zonal averaging leads to smoothing of distinct features, such as the tilted structure of the jet, seen in the winter climatology.In this work we propose a new feature-based method to diagnose the North Atlantic EDJ and its variability, based on 2-D maps of the low-level zonal wind field. We identify jet ‘objects’ based on contours of a minimum zonal wind threshold. By calculating moments of the objects, we can compute the jet latitude, tilt, intensity, and size. We show this method characterizes the North Atlantic jet structure more accurately and more robustly than the jet latitude index. We discuss insights into the morphology of the jet, brought to light by this new method. Most significantly, the distribution of jet latitudes shows a unimodal distribution rather than a trimodal structure, casting doubt on earlier interpretations of regime behavior in the North Atlantic EDJ. We further examine relationships between teleconnections and EOF-based circulation regimes with the jet morphology. Our approach provides a new, insightful diagnostic for EDJ dynamics.
