| Summary: | The North Atlantic Oscillation (NAO) is generally regarded to largely be a product of processes internal to the troposphere. This thesis investigates various aspects of how the NAO and related climatical fields are influenced by two of the tropospheric boundary components; the stratosphere above and the ocean below. The thesis consists of five manuscripts, three considering the role of the stratosphere, and two considering the role of the ocean. Data provided by the NCEP/NCAR re-analyses is used to investigate how anomalies in the stratospheric circulation relate to subsequent anomalies in various important climatic fields. The mean storm tracks are found to shift meridionally, although not symmetrically between the Pacific and the Atlantic regions (paper I). Following events of anomalously weak stratospheric circulation, a statistically significant shift in the storm track is found only over the Atlantic. The spatial temperature distribution is found to go through several spatially and temporally distinct stages (paper II). In key regions, including northern Asia, Europe and the oceanic areas off the east coast of North America, the probability of cold air outbreaks increases by 50 – 80% at various stages relative to the negative stratospheric circulation anomaly peak. The strongest cold air outbreak appears in Northern Asia several weeks before the stratospheric anomaly peaks. This cooling is associated with cold, northwesterly winds due to a strong high pressure anomaly centered above Northern Scandinavia. In a separate study (paper III), it is shown that this high pressure anomaly is a typical precursor of negative stratospheric circulation anomalies. It is found that it is associated with enhanced vertical wave propagation – which is known to favour negative stratospheric circulation anomalies. When the Scandinavian high precedes negative stratospheric circulation anomalies, the stratospheric anomalies become more intense, and stronger subsequent surface climate signals arise compared to events without a ...
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