Interannual teleconnection between Ural-Siberian blocking and East Asian winter monsoon

During boreal winter, the persistence of atmospheric blocking over Ural-Siberia (Ural-Siberia blocking, hereafter USB) favours successive development of the Siberian high, which potentially results in a long-lasting cold period in East Asia. Its significant contribution to some recent extremely cold episodes within the region, such as the persistent snowstorm taking place in southern China in early 2008, has aroused the concern of more in-depth analysis regarding the underlying physical mechanisms responsible for USB. Basically, the formation and maintenance of a USB involves an interaction between a cyclone coming from the Euro-Atlantic region and the Siberian high. In this study, the focus is put on how the extratropical and tropical climate factors collaborate to the dynamic linkage between USB and East Asian winter monsoon (EAWM) on interannual timescales.

We concern the combined effect of Arctic Oscillation (AO) and El Niño/Southern Oscillation (ENSO). The former factor plays a dominant role in the extratropical climate variability, including the occurrence of USB. When both the two factors are of the same polarity, their combined effect tends to enhance the USB-EAWM relationship. In particular, there is a distinct blocking frequency peak near the Ural Mountains and a consistent sign of temperature anomaly in the majority of EAWM. On the contrary, the USB-EAWM tends to be weaker when the two factors are out of phase. Under inconsistent forcing exerted by the extratropics and the tropics, the strength of the monsoonal flow in the northern and southern part of the EAWM diverges, which shows a stronger linkage with the AO and the ENSO respectively. In addition, the occurrence of blocking tends to be more distinguishable over the Euro-Atlantic region in lieu of the Ural-Siberia region. These results are vital for the predictability of the EAWM.