Interdecadal variations in winter extratropical anticyclones in East Asia and their impacts on the decadal mode of East Asian surface air temperature

Abstract

The interdecadal variations in extratropical anticyclone activity over East Asia during the winters of 1958–2013 were analysed using an objective identification and tracking algorithm for anticyclones. The influence of the interdecadal variation in anticyclone activity over the Mongolian Plateau on the interdecadal variation in East Asian surface air temperature and its possible mechanism was studied. The results showed that the Mongolian Plateau is the key region of anticyclonic activity in East Asia, and the occurrence frequency of anticyclones presented significantly opposite distribution forms in the higher and lower latitudes. An abrupt change in anticyclone activity over the Mongolian Plateau occurred in the late 1970s. From 1958 to the late 1970s, the main anticyclone activity occurred farther northward, whereas the activity was farther southward from the 1980s to 2013. Further study showed that in the period when the anticyclone occurrence frequency in the higher latitudes north of 50°N was lower (higher), while that in the lower latitudes south of 50°N was higher (lower), the surface air temperature of most parts of East Asia, especially the middle and high latitudes, was abnormally high (low). This was due to the anticyclonic activities, the Siberian high faded in the northwest part and expanded in southeast, while the East Asia trough and Ural Mountain blocking high weakened. This was also manifested as the variation in the geopotential height tendency forcing by transient waves. As the anticyclonic wave-breaking intensifies from western Mongolia to Northeast China, the high-frequency momentum flux over this area was significantly enhanced, strengthening the west wind in the higher latitudes from the north side and weakening the west wind in the middle latitudes from the south side. Under the combined force of the above activity, the southward movement of polar cold air was weakened, and the warm air in the middle and low latitudes was more easily transported to the north, resulting in warmer surface air temperatures over most parts of East Asia.