The Influence of Upper Level Jet Streams in East Asia on Climatic Effects of Eurasian Teleconnection Pattern in the Winter

Monthly NCEP/NCAR reanalysis dataset and temperature/precipitation data collected at 735 stations in China are used to investigate variations of Eurasian Teleconnection pattern (EU) and East Asian jet streams (EAJSs). The EU pattern shows a quasi-barotropic structure with obvious geopotential height anomalies at 250 hPa. In the positive EU phase, the East Asian polar front jet (PFJ) tends to be weakened and shifts northward; the subtropical jet (SJ) intensifies, inducing two well-separated branches. In the meantime, the Siberian High, the Aleutian Low, and the East Asian trough all strengthen. The situations in the negative EU phase are opposite to those in the positive phase. The close relationship between the EU and EAJSs plays an important role in the climatic effect of EU pattern. In positive EU phase, cold air from the high-latitudes moves southward due to strong meridional winds in the PFJ region and the winter temperature in China tends to be colder than normal. The warm air brought by the strong SJ and the cold air brought by the PFJ influence the distribution of precipitation anomalies in China. The concurrent variation of PFJ and SJ is the main mechanism for the EU to influence temperature/precipitation anomalies in China. After removing the years when the PFJ or SJ is strong, the obvious correlation between EU pattern and temperature/precipitation in China disappears. This result indicates that EAJSs can act as a bridge that links the EU signal with the variation of temperature/precipitation in China. Further study finds that the relationship between the EU and PFJ is more stable than that between EU and SJ. The configuration of PFJ and SJ is different even in the same EU phase. The non-unique configuration of EAJSs in the same EU phase provides an opportunity for EAJSs to influence the climatic effects of the EU pattern.