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Abstract:
The uncertainty in gravity wave (GW) parameterizations in conventional general circulation models has so far prevented a conclusive answer on how GWs, their interaction with the quasi-biennial oscillation (QBO), and the QBO itself may change in a warming climate. In this study, we therefore performed short explicit simulations of the QBO for different idealized climate states with the deep convection-permitting model ICON, which does not employ a parameterization of either deep convection or GWs. Thus, the QBO is entirely driven by explicitly resolved waves. Thereby, our simulations allow us to provide a very first direct estimate of how tropical GWs and the QBO may change in a warming climate.We find that a warmer climate results in a more vigorous generation of GWs by deep convection, resulting in a substantial increase of the lower-stratospheric GW momentum flux at phase speeds relevant for the QBO. As a consequence, the QBO downward propagation accelerates in the warmer climate states. Additionally, the dominant phase speed of the GW spectrum tends to increase in the warmer climate states, accompanied by a strengthening of the QBO jets in the upper QBO domain.We conclude that our results have qualitatively constrained potential changes in stratospheric GW momentum flux due to a warming climate and in view of this a warming-induced acceleration of the QBO seems to become increasingly likely. In a next step, we plan to extend some simulations to a longer time period to get a more comprehensive assessment of potential QBO changes in a warming climate.
