A global climatology of surface anticyclones, their variability, associated drivers and long-term trends

A global climatology of anticyclones identified at mean sea level pressure is presented based on multiple reanalyses over the period 1960-2016, including assessment of regional and seasonal variations, interannual variability, and long-term trends. Interannual variability is associated with the El Nino-Southern Oscillation (ENSO), particularly in the Pacific region during November-April. Anticyclones vary in phase with the strength and intensity of the local mean subtropical ridge, with anticyclone variability also associated with the Southern Annular Mode (SAM) in the Southern Hemisphere and the Arctic Oscillation (AO) in parts of the Northern Hemisphere, particularly during the cooler months of the year. Long-term climatological trends in anticyclone occurrence are presented, including back to 1960 using 20CR reanalysis data. The strongest trends occur in the Southern Hemisphere, including increases in anticyclone frequency in the latitudes 30-40S and decreases for adjacent latitudes in both seasons, which can be partially attributed to changes in SAM during November-April.