Connections between Eurasian teleconnection and concurrent variation of the upper-level jets over East Asia

Abstract:

The variation of East Asian jet streams (EAJS) associated with the Eurasian teleconnection (EU) pattern is investigated using 60-yr NCEP/NCAR daily reanalysis dataset over the period (1951-2010). The EAJS consists of three components: the polar front jet (PFJ), the plateau subtropical jet (PSJ), and the ocean subtropical jet (OSJ). Of the three jets over East Asia, the EU pattern exhibits significant influence on the PFJ and OSJ. There is a simultaneous negative correlation between the EU pattern and PFJ. A significant positive correlation is found between the EU pattern and OSJ with the EU leads the OSJ by about 5 days. There is no obvious correlation between the EU pattern and PSJ. The positive EU phase is accompanied by a weakened and poleward shifted PFJ, which coincides with an intensified OSJ. Meanwhile, the PFJ also moves westward while the OSJ migrates eastward. In negative EU phase, the PFJ is unusually strong and moves more southward, merging with the PSJ. A possible mechanism for the variation of EAJS during different EU phases is explored via analyzing the effects of 10-day high- and low-frequency eddy forcing. The zonal wind tendency due to high-frequency eddy forcing contributes to the simultaneous negative correlation between the EU and PFJ as well as the northward/southward shift of PFJ. Low-frequency eddy forcing is responsible for the westward/eastward shift of PFJ in company with the evolution of EU. High- and low-frequency eddy forcing are both responsible for the positive correlation between the EU and OSJ but only high-frequency eddy contributes to the lagged variation of the OSJ relative to EU. The negative correlation between the EU and temperature/precipitation anomalies in northern/eastern China sustains only when the PFJ and OSJ are out of phase with each other. Thus, the EAJS plays an important role in transmitting the EU signal to temperature and precipitation anomalies in East Asia.