A 30-35-year cycle period in cyclonic activity and rainfall regime for southeast Europe in 1948-2013 interval modulated by Atlantic Multidecadal Oscillation, North Atlantic Oscillation and Arctic Oscillation

The main goal of this study was to investigate the cyclonic activity and rainfall regime for the southeastern Europe in relation with large-scale oscillations like Atlantic Multidecadal Oscillation (AMO), North Atlantic Oscillation (NAO) and Arctic Oscillation (AO), between 1948 and 2013. Using the empirical orthogonal functions (EOF) analysis, simultaneously applied to daily average geopotential field time series at four different pressure levels (200, 300, 500 and 850hPa) during warm (April-September) seasons and over a synoptic spatial domain centred on Europe, the principal dynamic trait of the four mean geopotential fields was obtained. The analysis has shown that the first four eigenvectors describe about 81% of explained variance. The first eigenvector describes a positive relation between the upper and the lower geopotential fields in the western part of Europe and a negative relation in the southeastern part, in direct relation with the AMO. His projections evolution shows that, each year, the AMO phase modulates the changes in the geopotential fields from spring to summer and from summer to autumn. Positive AMO increases the summer period and negative AMO decreases it. NAO is being reflected in the second eigenvector, which describes a strong phase vertical oscillation of upper and lower geopotential field in northwestern Europe coupled with a smaller one in northeastern Europe in the first part of considered period and in both the second and third eigenvectors in the last part. The AO influence appears in the combination of the third and fourth eigenvectors in the middle part of the period. The combined dynamics of these four eigenvectors highlight a different dynamics of cyclonic activity and rainfall regime for Europe between 1948 and 1983, 1973 and 2006 and 1981 and 2013.