Interdecadal Variations of Wintertime Anticyclonic Activity in the Mongolian Plateau and Iranian Plateau

The NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis data from 1948 to 2013 is employed to investigate wintertime anticyclone activity and its decadal variability over Eurasia using an improved objective anticyclone detection and tracking algorithm. The results reveal that the high frequency distribution areas of the anticyclones are also areas of large climatic change of the anticyclones, especially in the Mongolian Plateau and Iranian Plateau, where the anticyclone activity is the most active. Therefore, both the decadal variability and long term trends are important features of climate change for extratropical anticyclones in Eurasia. The frequencies of the anticyclones in the Mongolian Plateau and the Iranian Plateau show obvious interdecadal variations. The occurrence frequency of the anticyclones shows significant periods of 2-6 years and 16-30 years in Eurasia, while the period often varies with time. The leading EOF (empirical orthogonal function) modes of the anticyclones in the Mongolian Plateau and Iranian Plateau for the 1948-2013 periods show a significant dipole-like distribution. The anticyclone activity has decreased in lower latitudes but increased in higher latitudes. The change in the intensity of anticyclones in the Mongolian Plateau can reflect the change in the intensity of the anticyclones over the Eurasian continent. The interdecadal variability of the movement of the distribution center of the anticyclones and their intensity in Eurasia can be explained by interdecadal variations of the position and intensity of the baroclinic front, which is mainly dominated by meridional temperature gradient in the lower troposphere. The influence of the baroclinic front on anticyclones in Eurasian is a regional phenomenon. The extratropical anticyclone changes in the Mongolian Plateau show a dipole-like structure with increases to the north of 50°N during 1960-1975 and to the south of 50°N during 1990-2005, which is associated with the southward shift of the baroclinic front from 55°N to 45°N within 80°-120°E of the region. However, the decadal latitudinal change in the baroclinic front within 30°-80°E cannot fully explain the dipole-like structure of changes in anticyclones over the Iranian Plateau. Since the middle 2000s, the intensified Eurasian anticyclones are caused by the intensified baroclinic front.