The North Atlantic Oscillation (NAO) is the major mode of atmospheric winter variability over the North Atlantic. Its current state has long been described by the station‐based NAO Index. This index has been shown to represent winter temperature anomalies over Northern Europe well. Nonetheless, its positions of measurement are stationary and may not catch the moving NAO-pattern’s characteristics sufficiently well to best represent the Scandinavian winter temperature anomalies. A new index based on North Atlantic maximum and minimum sea level pressure (SLP) is introduced in this study (called NAOE Index). The points of NAOE Index are therefore moving over the North Atlantic SLP‐field and may better catch atmospheric processes affecting Scandinavian winter temperature anomalies. NAOE Index correlation with Scandinavian winter temperature anomalies is analyzed through NASA’s (National Aeronautics and Space Administration) MERRA‐data (Modern Era‐Retrospective analysis forResearch and Applications). This study shows that NAOE Index represents the Scandinavian winter temperature anomalies almost as well as NAO Index from observed values does. The indices are alsowell correlated with each other. The direct difference between maximum and minimum SLP is also analyzed with regard to the Scandinavian winter temperature anomalies. The SLP‐differences are class‐divided and their correlations to the class‐mean temperature anomaly are shown to be very high. This correlation issignificantly higher than the correlations of temperature and each index. Hence, the results from this study suggest that an index based on the direct extreme‐SLP‐difference is preferred for representing the NAO’s impact on Scandinavian winter temperature anomalies. This study gives additionally a comprehensive view of NAO. Studies concerning the NAO’s history of research, dynamics, temperature connections and secondary impacts are reviewed.

No description available.

Winter storms can have devastating social and economic impacts in Europe. The severity of storms and the region they influence (southern or northern Europe) is related to the index of the North Atlantic Oscillation (NAO). However recent findings indicate that over the last millennium the relationship between the NAO and storminess varied and the forcings over centennial timescales are debated. Therefore in this research storminess has been reconstructed from NAO-sensitive regions of southern Europe (Galicia, Spain) and northern Europe (Outer Hebrides, Scotland), to investigate the Late Holocene NAO-storminess relationship and the causes of observed variability. Reconstructions were based on measurements of aeolian sand deposits within ombrotrophic peat bogs and a lake sedimentary archive from the Hebrides. The elemental composition of the lake sediments were analysed (using ITRAX XRF core scanning) to identify aeolian/in-washed sediment resulting from storms, as confirmed by correlations with instrumental data. As this is a relatively new technique there was a methodological focus on assessing its applicability for storm reconstructions and the maximum resolution achievable. It is concluded the reconstruction had a 10-year resolution (equivalent to 2-5 mm sampling resolution). The peat bog reconstructions span 4000 cal yr BP to present and indicate that there was a Late Holocene northward storm track shift. The results suggest that storminess was high in Galicia between 4000-1800 cal yr BP, after which it decreased and then gradually increased in the Outer Hebrides after 1500 cal yr BP. Comparison with an NAO reconstruction supports a consistent NAO-storm relationship through the Late Holocene. Orbital forcing is suggested as causing a steepening of the latitudinal temperature gradient and increasingly zonal circulation. Superimposed on this trend are centennial variations, which spectral analysis and visual comparisons suggest are primarily the result of solar minima (suggested as causing a weakened latitudinal temperature gradient and meridional circulation patterns), with some additional forcing from volcanic and oceanic changes. Therefore there has been a consistent storm-NAO relationship through the Late Holocene; however there appear to have been millennial and centennial shifts as the result of hemispheric circulation reorganisations.

Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xvii, 147 p.: ill. Includes abstract and vita. Advisor: David H. Bromwich, Dept. of Geography. Includes bibliographical references (p. 140-147).

The Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) are the most pronounced modes of extratropical atmospheric wintertime variability in the Northern Hemisphere. This thesis investigates different aspects of the AO and NAO on the in traseasonal and seasonal time scales. First, the question of how the differences between the AO and NAO are influenced by the choice of the definitions of the NAO and to what extent the AO and NAO differ from each other is investigated using the daily NCEP/NCAR reanalysis data spanning 51 boreal winters. One AO index and four different NAO indices are used in this study. It is found that the AO and NAO are quite similar to each other when both are defined using pattern-based indices, while some notable differences are observed between them when the NAO is defined using a station/gridpoint-based index. Then the predictability of the AO and NAO is examined using a simple general circulation model (SGCM). Numerical experiments are performed to determine the sensitivity of the setup processes of the AO and NAO to the details of the initial conditions. The predictive skills for the AO and NAO are compared to each other. Finally, the potential role of tropical Pacific forcing in driving the seasonal variability of the AO is explored using both observations and the SGCM. The results indicate that a negative thermal forcing over the western tropical Pacific and a positive forcing north of the equatorial mid-Pacific play important roles in producing an AO-like atmospheric response.

Thesis (M.S.)--University of Delaware, 2008. / Principal faculty advisor: Daniel J. Leathers, Dept. of Geography. Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xv, 200 p.; also includes graphics. Includes bibliographical references (p. 173-184).

Thesis (M.Sc.). / Written for the Dept. of Atmospheric and Oceanic Sciences. Title from title page of PDF (viewed 2009/06/23). Includes bibliographical references.

No description available.

Waves in the North Atlantic are strongly seasonal, and peak in the winter season. The west coast of Portugal is exposed to winter swell, generated by wind associated with North Atlantic extratropical cyclones. The track of these storms, generated near the North America east coast, is strongly influenced by the North Atlantic Oscillation (NAO). When the NAO is in its positive phase they normally track northeast and reach Western Europe well north of the Iberian Peninsula, in the British Islands or Scandinavia. However, in the negative NAO situation,the track of the storms is more zonal and south than usual, due to a weakened NAO. The characteristics of wave regime in Portugal are shown to be strongly related to the NAO phase and corresponding storm tracking. Positive NAO storms, tracking northeast towards the north of Europe, drive longer period swell from the northwest, whereas negative NAO storms have associated shorter period swell arriving to Portugal from a more westerly direction. The relation between the NAO phase and the storm tracks and the characteristics of the wave regime is investigated with ten year observations from four directional waverider coastal buoys, located off the coast of Portugal.