The eddy-driven jet (EDJ) over the North Atlantic drives variability in weather and climate over Europe, yet its characterisation has relied on zonally averaged diagnostics that mask its full spatio-temporal complexity. This thesis develops and applies a novel two-dimensional object-based framework to extract key EDJ features such as the latitude, strength, and tilt measured using the daily 850hPa zonal wind fields. The object method shows a unimodal climatologtical distribution of EDJ latitude, in contrast to the trimodal distribution found for the conventional Jet Latitude Index (JLI). The difference is shown to be partly due to the poor performance of the JLI when the jet is weak, broad, tilted or split.
Using this new framework, I demonstrate robust links between EDJ configurations and large-scale modes of atmospheric variability: southerly, weak, and positively tilted jets coincide with negative NAO/East-Atlantic phases and enhanced surface blocking; conversely, northerly, strong, and negatively tilted jets coincide with positive NAO conditions and zonal flow. Using data from the seasonal forecasting model GloSea5, I show that models have skill in predicting the winter EDJ latitude but have no skill for the EDJ tilt and strength. The skillful forecasts for the EDJ latitude exhibit a weak signal-to-noise ratio comparbale to what has been found for the winter NAO.
Finally, I investigate the influence of teleconnections from ENSO, QBO, and MJO with the new methodology. El Niño favours early winter poleward, stronger, westward tilted jets, while La Niña produces the opposite shifts; easterly QBO phases promote persistent equatorward, weakened jets; and certain MJO phases modulate EDJ onset and tilt on subseasonal timescales. These results underscore the importance of multidimensional jet diagnostics for improved understanding and prediction of mid-latitude climate variability and extremes.
