Rieke, Ole (2018) The nonstationarity of the summer east Atlantic pattern and its tropical-extratropical teleconnection. (Bachelor thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 51 pp.

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Abstract

Over the last 40 years, the Summer East Atlantic pattern has been the second most dominant mode of interannual variability in summer season over the North Atlantic European region after the Summer North Atlantic Oscillation. Previous studies found that the pattern has high impact on precipitation and temperature in Europe, causing very hot summers in central Europe when in its positive state. The pattern was also found to be related to tropical forcing by diabatic heating anomalies in the tropical Pacific and Caribbean that might be associated with the developing El Niño, resulting in a certain amount of predictability of the pattern. The aim of this thesis was to investigate the pattern in a preindustrial control run of the Max-Planck-Institue Earth System Model with a length of 700 years. It was found that, although the results could be verified in general, the Summer East Atlantic pattern itself, but also its impact on European climate and its tropical forcing, are highly nonstationary over time. Evidence is provided that the latest 40 years rather represent the current state of the Earth System than a constant condition, suggesting that future developments of the pattern might be different. Based on the finding that the last 40 years represent the maximum of tropical forcing and impact of the Summer East Atlantic pattern that was found in the model run, a future decrease of both its influence and its tropical forcing can be expected. Further mechanisms and possible reasons for this lack of robustness are presented. Furthermore, the influence of anomalies in sea surface temperature that are already present in the preceding spring on the pattern is analysed suggesting that this relation is connected to the tropical forcing by diabatic heating.

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