A Strengthened Teleconnection of the Quasi-Biennial Oscillation and Tropical Easterly Jet in the Past Decades in E3SMv1

The stratospheric quasi-biennial oscillation (QBO) has a significant influence on the tropical troposphere. The tropical easterly jet (TEJ) is a component of the Asian summer monsoon. The Energy Exascale Earth System Model version 1 (E3SMv1) can generate the QBO internally and simulate the cooling of the temperature near the tropopause during the easterly QBO (EQBO). E3SMv1 reveals that during the EQBO the stability in the upper troposphere over the Indian Ocean (IO) is decreased more than over the western Pacific, resulting in anomalous upward motions over the IO and anomalous downward motions over the western Pacific, which is potentially contributing to the westerly wind anomalies in the TEJ. The opposite occurs during the westerly QBO (WQBO). In the AMIP-historical simulations forced by significantly warmer IO sea surface temperature, a stronger correlation between the QBO and TEJ indices is observed in the recent decades compared to the period before 1980, which is closer to reanalysis. A possible explanation is that the long-term changes in both stability and upward motion in the upper troposphere over the IO are important factors to influence the change in the teleconnection between the QBO and TEJ. The comparison of the AMIP-historical and the ocean-coupled historical simulations shows that the warming of the Indian Ocean has played a vital role in the strengthened QBO-TEJ teleconnection over the past six decades.