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

The Energy Exascale Earth System Model version 1 (E3SMv1) is a new global model that can generate a weakened tropical easterly jet (TEJ) during the easterly quasi‐biennial oscillation (EQBO) and a strengthened TEJ during the westerly QBO (WQBO), which is referred to as the QBO‐TEJ teleconnection. Although the longitudinal structure of the QBO‐TEJ teleconnection is different between reanalysis and simulations, we hypothesize that simulations can still provide insights into the observed long‐term changes in the QBO‐TEJ teleconnection. The Atmospheric Model Intercomparison Project historical simulations (AMIP‐historical) generate a strengthened trend in the correlation between the QBO and TEJ indices in the period of 1950–2014 as in reanalysis. The comparison of the AMIP‐historical and the Coupled Model Intercomparison Project coupled historical simulations (coupled‐historical) shows that the warming of the Indian Ocean has played a vital role in the strengthened QBO‐TEJ teleconnection over the past six decades. Plain Language Summary 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. 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. Key Points E3SMv1 produces a weakened/strengthened tropical easterly jet (TEJ) during the easterly/westerly QBO The correlation between quasi‐biennial oscillation (QBO) and TEJ is stronger in the recent past than pre‐1980 in ERA5 and