Abstract
This paper presents the effect of the North Atlantic Oscillation (NAO) on the thermal characteristics of lakes in Poland. In the analysis, the use was made of monthly air temperatures recorded at fifteen meteorological stations, water temperatures of twelve lakes, and Hurrell’s winter NAO indices. Over the study period (1971–2010), there was a marked increase in the temperatures of both, air and lake waters. Depending on the NAO phase, water temperatures were observed to depart from mean values, being markedly higher than average (even by 1°C) in the positive winter NAO phase. The differences in water temperatures were statistically significant in the winter-spring season. In turn, in the negative NAODJFM phase lake water temperatures in winter and spring were markedly lower than average (in March even by 1.0°C). The unique response of some lakes depends on their morphometric parameters, including their mean depth.
Highlights
The pattern of processes and phenomena occurring in lakes results from global range-factors, local conditions in their catchments, and their individual morphometric parameters
The distribution of air temperatures obtained in the study period (1971-2010) for the fifteen weather stations shows annual means to decrease from west to east, which is connected with a stronger impact of the continental climate in the east of Poland, as observed by Ewert (1973)
The research has proved the North Atlantic Oscillation to have a big influence on the temperature of both, air and lake waters in the study area
Summary
The pattern of processes and phenomena occurring in lakes results from global range-factors (air circulation, radiation level), local conditions in their catchments (use pattern, hypsometry, etc.), and their individual morphometric parameters (area, depth, etc.). The NAO affects climatic conditions the strongest in winter, and in the other seasons high values of its index are accompanied by higher-than-average air temperatures in western Europe (Carleton 1988, Rogers 1997, Trigo et al 2002) It determines climatic conditions in Poland by causing an increase in temperature in the cold season of the year (Marsz and StyszyĔska 2001, Przybylak et al 2003) and influencing radiation and humidity conditions (BryĞ and BryĞ 2002), precipitation (StyszyĔska 2001, Wibig 2001), as well as the duration and thickness of snow cover (Falarz 2007). Changes in the heat balance of lakes brought about by the NAO transform the conditions of biological life in those ecosystems (Straile and Adrian 2000, Ottersen et al 2001)
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