Winter air temperature in Warsaw depending on the NAO index and the regional circulation

The paper discusses the circulation and thermal conditions over Poland and their dependence on the sign and values of the North Atlantic Oscillation (NAO) index (hereinafter NAO+ and NAO-). The input data used in the research consisted of average monthly values of air temperature in Warsaw, NAO index values, and a calendar of atmospheric circulation types according to Litynski (1969). The study comprised the three winter months (December, January,February) from the period 1951-2015. The dependence between the circulatory and thermal conditions was investigated on the basis of 10 months representing each of the winter months with the highest NAO+ and NAO-values and 10 months with the greatest positive and negative temperature deviations from the long-term average (Delta t+, Delta t-), based on the assumption, that they should largely be the same months. In general, the analysis confirmed these assumptions, but it also showed that there are deviations from previously known regularities as regards the effect of the positive or negative phases of the NAO on the thermal conditions in Poland.