Institute of Computer Science, Academy of Sciences of the Czech Republic
Pod vodárenskou vezí 2, 182 07 Prague 8, Czech Republic
Institute of Atmospheric Physics, Academy of Sciences of the Czech Republic
Bocni II/1401, 141 31 Prague 4, Czech Republic
Daily mean near-surface air temperature series from seven European locations were processed in order to obtain reliable estimates of instantaneous phases of the annual cycle as an objective measure of timing of seasons. The recent changes of the latter do not depart from the range of natural phase fluctuations observed in the historical temperature records. Significant, geographically dependent correlations of the phase fluctuations with the North Atlantic Oscillation index, as well as weaker, negative correlations with the El Nino Southern Oscillation index have been observed.