CLIMATE SIGNALS OF THE NORTH ATLANTIC OSCILLATION DETECTED IN THE CARPATHIAN BASIN

Abstract

North Atlantic Oscillation (NAO) can be considered as the primary large scale atmospheric driver of the European climate, especially in winter. In the present paper, first, NAO effects on regional circulation represented by the circulation patterns (CP) using the Hess-Brezowsky Grosswetterlagen (HBGWL) and Peczely classification systems are analyzed. Our results for the 1901-2000 period suggest that the zonal/meridional CP classes occur more often during NAO+/NAO- phase in all seasons in case of both classification systems. Furthermore, Cyclonic/Anticyclonic CP types are more/less frequent in NAO- phase, and less/more frequent in NAO+ phase than in case of normal conditions. Then, NAO and CP joint effects on local temperature and precipitation time series are evaluated for the 20th century. In general, NAO- phase is associated with cold and wet winters, whereas NAO+ phase implies warm and dry winters in the Carpathian basin. If considering cyclone or anticyclone dominance over the region, NAO+ is associated with dry and warm winters, and dry summers in case of Anticyclonic CP class, whereas NAO- phase implies wet and cold winters and autumns in the Carpathian basin (either for the Peczely or the HBGWL classification systems). When Cyclonic CP class occurs using the HBGWL classification system (i) winters tend to be drier and warmer than usual, springs tend to be drier and colder than usual in NAO+ phase; (ii) springs and autumns tend to be wetter than usual, winters tend to be colder than usual in NAO- phase. If the Peczely classification system is used then Cyclonic CP class is associated with (i) significantly warmer winters and colder springs during NAO+ phase; (ii) significantly wetter and colder winters, and wetter autumns during NAO- phase.