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CR 28:221-228 (2005)  -  doi:10.3354/cr028221

Thermal effects of the North Atlantic Oscillation on the cold period of the year in Lithuania

Arunas Bukantis1,*, Galina Bartkeviciene2

1Department of Hydrology and Climatology, Vilnius University, M. K Ciurlionio 21, 03101 Vilnius-9, Lithuania
2Department of Terrestrial Ecosystems, Institute of Ecology, Vilnius University, Akademijos 2, 08412 Vilnius-21, Lithuania

ABSTRACT: The impact of the North Atlantic Oscillation (NAO) on long-term air temperature fluctuations in Lithuania was studied for the period 1865 to 2000. Mean monthly values of 2 NAO indices (NAO-1, NAO-2) and air temperatures at 9 Lithuanian meteorological stations were used as references. Synoptic situations, as well as the mean sea level pressure (SLP) and 500 hPa geopotential height field of a total of 265 months, were analysed. NAO conditions were classified as positive, negative or neutral. air temperature fluctuations in Lithuania during the cold period of the year (November to March) are positively correlated with fluctuations of the NAO indices. During periods of extreme NAO indices (| I | > ±1.5σ), a negative NAO phase is usually correlated (75 to 88% of the cases) to negative temperature anomalies, whereas a positive NAO phase is correlated to positive temperature anomalies. In the other cases, reserve impact of positive and negative NAO patterns, the relation between NAO phases and regional temerature anomalies is opposite or not detectable . Also, this study includes the analysis of atypical periods of NAO like circulation: when positive NAO phase was related to negative temperature anomalies and negative NAO phaase to positive temperature anomalies in Lithuania.

KEY WORDS: NAO · Indices · temperature anomaly · Lithuania · synoptic climatology

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