Regionalisation of the precipitation pattern in the Baltic Sea drainage basin and its dependence on large-scale atmospheric circulation

Regionalisation of precipitation in the Baltic Sea drainage basin was realised using the principal component analysis of gridded monthly precipitations during 1900-1996 obtained from the global land precipitation dataset created in the University of East Anglia. Four main precipitation regions were determined for the Baltic Sea drainage basin: northern, eastern, southern and western. The latter contains also the Baltic Sea. Significant relationships were found between atmospheric circulation and precipitation, being the strongest in winter and the weakest in summer. Circulation variables indicating the intensity of westerlies were usually positively correlated with precipitation in windward regions during the cold part of the year. The area with the highest correlation was located in the Scandinavian Mountains. Lower positive correlations were revealed also in Denmark, southwestern Sweden, Lithuania, Latvia, Estonia, Finland and northwestern Russia. A different relationship was typical to the leeward side of westerlies in most of Sweden. Even a negative correlation was found with the circulation variables describing the intensity of westerlies. Precipitation in Sweden was mostly related to the airflow from the Baltic Sea expressed by the circulation form E. The teleconnection patterns (North Atlantic oscillation, East Atlantic, Polar/Eurasia, East Atlantic/West Russia, Scandinavian) had high correlations in specific regions at certain seasons.