Frequency of the winter temperature extremes over Siberia dominated by the Atlantic Meridional Overturning Circulation

Abstract

Widespread observed and projected increases in warm extremes, along with decreases in cold extremes, have been confirmed as being consistent with global and regional warming. Here we disclosed that the decadal variation in the frequency of the surface air temperature (SAT) extremes over Siberia in winter was primarily dominated by the Atlantic Meridional Overturning Circulation (AMOC) rather than anthropogenic forcing. The stronger AMOC induced more warm and cold extremes through increasing the variance of winter SAT over Siberia while the direct effect of external forcings, especially anthropogenic greenhouse gases, had little impact on the summation of warm and cold extremes due to equivalent effects on the increases in warm extremes and decreases in cold extremes. The possible mechanism can be deduced that the stronger AMOC stimulated the propagation of the wave train originated in the North Atlantic Ocean, across mid- to high latitudes, thereby increasing the variabilities in the circulations over the Ural blocking region and Siberia, which are critical to the SAT extremes there.