Linkage between the East Asian January temperature extremes and the preceding Arctic Oscillation

This study investigated the potential connection of the October-December Arctic Oscillation (AO-OND) with the following January East Asian temperature extremes and the possible mechanisms. It was found that the extreme cold (warm) events are less (more) frequent in January over East Asia following a positive phase of AO-OND, which might be attributed to the intrinsic persistence of AO-OND in stratosphere and the memory of Eurasian snow cover. It is revealed that the barotropic structure of AO-OND could extend to stratosphere. By the following January, wave activities propagate from stratosphere downwards to upper troposphere, then bent equatorwards to mid-latitudes. Consequently, the January circumpolar jet (polar vortex) gets strengthened (colder) because the equatorward-pointing (upwards) wave activities correspond to poleward meridional eddy momentum (eddy heat) flux. In such a way, the anomalous AO-OND persists into the following January. On the other hand, positive phase of AO-OND causes significant surface warming in most parts of Eurasia, leading to Eurasian snow melt. The October-December snow melt has intrinsic climatic memory and further weakens the January Siberian High through reducing surface albedo. Besides, the surface warming in North Europe because of reduced surface albedo caused by snow melt could stimulate a Rossby wave train propagating eastwards across Eurasia, which restrains the blocking events around Ural region. In such a context, the incidence of extreme warm (cold) events over East Asia is more (less) frequent.