Atmospheric circulation variability in Europe and northern Asia (1901 to 2010)
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ORIGINAL PAPER
Atmospheric circulation variability in Europe and northern Asia (1901 to 2010) Andreas Hoy & Mait Sepp & Jörg Matschullat
Received: 12 January 2012 / Accepted: 9 September 2012 # Springer-Verlag 2012
Abstract Climate variability in Europe and northern Asia is markedly affected by changes in atmospheric circulation. Two manual catalogues of large-scale circulation patterns, the ‘Grosswetterlagen’ (GWLc) and ‘Vangengeim-Girs’ classifications (VGc), were analysed and compared to detect frequency changes of circulation forms. Results were compared with variations of ‘objective’ references: variations of the North Atlantic Oscillation (NAO) and a hybrid version of the GWLc (SynopVis Grosswetterlagen catalogue, SVGc). Changes were investigated for 1901–2010, focussing on the most recent climate normal (1981–2010). Trends are moderate in the winter half year (WHY), but rather consistent between the approaches. Circulation variability within VGc/NAO and GWLc/SVGc largely agrees. In the summer half year, large trends are visible in VGc and GWLc, but their objective support by the SVGc, showing comparably small changes, is low. Changes in the distribution of circulation patterns likely fostered a larger temperature increase in the investigated regions compared to global average temperatures during the past 30 years in the WHY. The results of this study help further in investigating temperature and precipitation changes in both Europe and northern Asia.
A. Hoy (*) : J. Matschullat Interdisciplinary Environmental Research Centre, TU Bergakademie Freiberg, Brennhausgasse 14, 09599 Freiberg, Germany e-mail: [email protected] M. Sepp Department of Geography, Institute of Ecology and Earth Sciences, University of Tartu, Vanemuise 46, 51014 Tartu, Estonia
1 Introduction Climate variability in Europe and northern Asia is largely affected by atmospheric circulation (Baur et al. 1944; Girs 1971; Girs and Kondratovich 1978; Tveito and Ustrnul 2003). Prevailing westerlies, for instance, cause distinctively higher winter temperatures in Europe (including its Russian territories) than in other parts of the northern hemisphere at similar latitudes. The intensity of westerlies is unstable and fluctuates markedly over time (Hurrell 1995; Sepp and Jaagus 2002; IPCC 2007). Their strength is often described by circulation indices, e.g. the widely used North Atlantic Oscillation (NAO) index. The NAO index is determined by variations of their two centres of action, the Icelandic low and the Azores high (Walker 1924; van Loon and Rogers 1978; Hurrell 1995; Hurrell and van Loon 1997; Hurrell et al. 2003), resulting in large-scale impacts on European and northern Asian climate. Catalogues of atmospheric circulation, on the other hand, allow obtaining a more precise picture of the regional peculiarities of westerlies. Generally, those catalogues are frequently used to investigate climate variability based on a predefined number of circulation patterns (types). Those types are chosen, e.g. according to position and mo
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