Determinacy of Temporal Variability of Cyclone Frequency in the Black Sea–Mediterranean Region

This paper investigates features of seasonal variability of cyclonic activity and estimates the separate and combined contribution of quasi-periodic climatic processes of interannual-multidecadal scale to the variability of cyclone frequency. Such knowledge is important for the diagnosis and prediction of weather and climate anomalies. Cyclone parameters are obtained for the Black Sea region and the Western and Eastern Mediterranean using four-term data sets of 1000-hPa geopotential height from the NCEP/NCAR reanalysis in 1951–2017 and M.Yu. Bardin’s methodology. Analysis of the spatiotemporal distribution of climatic values shows that cyclonic activity increases in winter, decreases in summer, while in the Black Sea region, the maximum frequency of cyclones is shifted to spring (April). High cyclonic activity throughout the year with the lowest variance is observed in the Western Mediterranean, and the greatest spread in cyclone parameters is mainly in the Black Sea region. In the Eastern Mediterranean, the frequency of cyclones is higher in winter and lower in summer than in the other two regions, which causes the maximum amplitude of the annual variation. Using determination coefficients, it is shown how much of the cyclone frequency variance with a time delay of 0–11 months can be explained by the variability of known quasi-periodic climatic processes of interannual-multidecade scale. The predominant individual contribution of the North Atlantic Oscillation, along with the Arctic and East Atlantic oscillations in some months, is shown for the cyclone frequency in the Black Sea region (20–30% of the explained frequency variance in winter). About 10–15% of the frequency variance is explained by the contribution of the Pacific Decadal Oscillation, the Scandinavia pattern, the Mediterranean Oscillation and the Tropical/Northern Hemisphere pattern, as well as the East Atlantic/Western Russia pattern in spring and the Polar/Eurasian pattern in summer and autumn. The main contribution to the variability of the cyclone frequency in the Western Mediterranean is made by the Scandinavia pattern (more than 20% of the variance in spring), East Atlantic/Western Russia pattern, East Atlantic Oscillation (each about 15% of the variance), Mediterranean and Western Mediterranean oscillations (each 10–15% of the variance). About 10% of the variance of the average annual frequency is caused separately by the Pacific/North American and West Pacific patterns; 5–10% of the variance of the winter frequency is caused separately by the El Niño–Southern Oscillation and Tropical/Northern Hemisphere pattern. The variability of the cyclone frequency in the Eastern Mediterranean is mainly determined by the regional Mediterranean patterns; in spring, by the Polar/Eurasian pattern and East Atlantic Oscillation. At the same time, 10–20% of the variance of the annual and winter frequency of cyclones is associated separately by the Pacific/North American, East Pacific/North Pacific and West Pacific patterns; 5–10% of the variance of the spring frequency is the individual contribution of the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation. Analysis of multiple linear regression allowed us to estimate the combined contribution of the considered 15 climatic patterns to the variability of the cyclone frequency, which, even taking into account only linear synchronous manifestations, makes up 60–70% of the explained frequency variance in the winter–spring period and for annual averages.