Multidecadal change of winter cyclonic activity in the Mediterranean associated with AMO and PDO

Abstract

The paper is devoted to analysis of the cold half-year (October to March) frequency of cyclones in the Mediterranean-Black Sea region associated with the global processes in the ocean-atmosphere system-the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO). Firstly, climatic conditions in the North Atlantic-European region during positive and negative phases of these global oscillations were shown using NCEP/NCAR reanalysis data for 1948-2016 and data of the NASA GISS Atlas of Exratropical Strom Tracks in 1961-1998. Mean monthly values/anomalies (composites) for equal periods of the negative and positive AMO and PDO phases were calculated and compared. The results of the study support the idea that the Pacific and Atlantic influence on the climatic (multidecadal) scale is realized via change of the large-scale fields of the North Atlantic anomalies typical for the interannual scale. Then spatial distribution of the frequency of cyclones in the Mediterranean-Black Sea region was obtained using global NCEP/NCAR reanalysis data sets on 1000 hPa geopotential height in 1948-2013. It was shown that during the positive AMO phase, frequency of cyclones in the Mediterranean was higher by absolute values in November to March over the Tyrrhenian and Ionic Seas and lower over the Anatolian peninsula. During the negative PDO phase, frequency of cyclones over the Anatolian peninsula in January to March is significantly higher than in the positive PDO phase.