Krüger, Julian (2020) Characteristic Jet Stream patterns related to European Heat Waves. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 57 pp.

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Abstract

The 21st century has seen an increase in mid-latitude extreme weather events. This thesis examines whether heat wave occurrences in 2003, 2010, 2015 and 2018 are linked to characteristic jet stream patterns. A potential link between North Atlantic sea surface temperatures (SST’s), the jet stream and European surface temperatures is evaluated with particular emphasis on the heat wave 2018. Previous studies suggested a link between cold North Atlantic SST’s anomalies prior to heat wave occurrences over Europe. Other studies proposed a mechanism, called QRA (Quasi-Resonant Amplification) mechanism, combining a double jet presence with quasi-stationary and highly-amplified Rossby wave events as a response, increasing the likelihood of heat wave conditions. In this thesis the relationship between remarkable anomalies during summer 2018 and both mechanisms is studied. This thesis demonstrates that central and northern Europe have experienced extremely hot and dry conditions during May and July 2018. An anomalously cold North Atlantic from spring to early summer is linked to a strong double jet behaviour evident in the Atlantic-European sector and to the high temperatures over Europe in summer 2018. This thesis confirms via correlation as well as composite analysis of ERA-Interim reanalysis data, that generally persistent cold North Atlantic SST anomalies are more likely to induce the development of a double jet a few weeks afterwards, leading to a strongly undulated jet stream. The jet stream has a preferred phase position in the North Atlantic-European sector. These conditions initiate enhanced surface temperatures over the European continent. The analysis supports that the coexistence of cold SST anomalies and warm surface temperatures over Europe are linked to an amplified and persistent trough-ridge system across the North Atlantic-European sector supporting a relationship between the two proposed mechanisms involving North Atlantic SST anomalies as well as wave resonance and amplification. The analysis reveals similar conditions for previous heat waves in 2003 and 2015. By contrast, the Moscow heat wave in 2010 might had different drivers since no significantly negative North Atlantic SST anomalies and no double jet structure is found. This thesis evaluates and confirms a link between the North Atlantic SST’s and the QRA mechanism for the first time. North Atlantic SST’s are important to investigate since they likely act as a precursor for the generation of the QRA mechanism and thus also for European heat wave occurrences.

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