Impacts of Winter Arctic Oscillation on the Siberian High, the East Asian Winter Monsoon, and Sea-Ice Extent

Using the NCEP/NCAR reanalysis dataset for a 40-year period from January 1958 to December 1997, we investigate relationships between winter Arctic Oscillation (AO) and Siberian High (SH), and the East Asian winter monsoon (EAWM). The results indicate that winter AO not only influences climate variations in the Arctic and the North Atlantic sector, but also significantly affects winter SH, and further influences EAWM. When winter AO is in its positive phase, winter SH and EAWM are weaker than normal. Thus, the northern SH drops about 1-3 hPa, while its southern part rises less than 2 hPa. Correspondingly, air temperature from near the surface to the middle troposphere is about 0.5-2(C higher than normal in the southeastern Siberia and the East Asian coast, including eastern China, Korea, and Japan. When AO reaches its negative phase, an opposite scenario can be observed. This study also indicates that winter SH have no significant effects on climate variations in Arctic and the North Atlantic sector. Its influence intensity and extent are obviously weaker than AO, exhibiting 'local' feature compared with AO.

The study further reveals the mechanism of how the winter AO relates to winter SH. It is found that winter SH has closely association with both dynamic processes and air temperature from the surface to the middle troposphere. The western SH mainly depends on dynamic processes associated with AO, and its eastern part is more closely related with air temperature. The maintaining of winter SH mainly depends on downward motion of airflow of the nearly entire troposphere. The airflow originates from the North Atlantic sector, and its variation is influenced by the AO. When AO is in its positive (negative) phase, downward motion remarkably weakened (strengthened), which further influences winter SH.

Key words: Arctic Oscillation (AO), Siberian High, East Asian Winter Monsoon