Impact of Tropical Pacific Precipitation Anomaly on the East Asian Upper-Tropospheric Westerly Jet during the Boreal Winter

The leading mode of boreal winter precipitation variability over the tropical Pacific for the period 1980-2010 shows a west-east dipole pattern with one center over the western North Pacific (WNP) and Maritime Continent and the other center over the equatorial central Pacific (CP). Observational evidence shows that the variability of the East Asian upper-tropospheric subtropical westerly jet (EAJ) has a significant correlation with precipitation anomalies over the WNP and CP and that tropical precipitation anomalies over WNP and CP have a distinct influence on the variation of the EAJ. A series of numerical experiments based on a linear baroclinic model are performed to confirm the influence of the heating anomalies associated with precipitation perturbations over the WNP and CP on the EAJ. The results of numerical experiments indicate that a heat source over the WNP can excite a northward-propagating Rossby wave train in the upper troposphere over East Asia and facilitate a poleward eddy momentum flux. It results in the acceleration of the westerlies between 30 degrees and 45 degrees N, which favors a northward displacement of the EAJ. The response induced by a heat sink over the CP features a zonal easterly band between 25 degrees and 40 degrees N, suggesting that the response to heat sink associated with negative precipitation anomalies over the CP may weaken the EAJ. A strengthened relationship was found between tropical Pacific precipitation and the EAJ since 1979. The modeling results suggest that the shift of mean states might be responsible for the strengthened EAJ-rainfall relationship after 1979.