• Principal component analysis;
  • Weather types;
  • Atmospheric circulation;
  • Climatic change


Principal component analysis is applied to annual weather type frequencies for the British Isles. The results objectively define characteristic relationships between the different types, and are used to determine changes in the atmospheric circulation in the region of the British Isles over the period 1861 to 1980. It is shown that, as far as annual frequencies are concerned, only six (of the 27) weather types are needed to define and monitor changes in the atmospheric circulation.

The component amplitudes are correlated with temperature and rainfall data, and physically reasonable relationships are identified. The analysis is extended to the period 1781 to 1785, and similarities are found between the extremes experienced during that period and during the 1970s.