17 Nov 2023
 | 17 Nov 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Crucial role of obliquely propagating gravity waves in the quasi-biennial oscillation dynamics

Young-Ha Kim, Georg Sebastian Voelker, Gergely Bölöni, Günther Zängl, and Ulrich Achatz

Abstract. In climate modelling, the reality of simulated flows in the middle atmosphere is largely affected by the model's representation of gravity wave processes that are unresolved, while these processes are usually simplified to facilitate computations. The simplification commonly applied in existing climate models is to neglect wave propagation in horizontal direction and time. Here we use a model that fully represents the propagation of unresolved waves in all directions, thereby elucidating its dynamical effect upon the climate mode in the tropical stratosphere, namely the quasi-biennial oscillation. Our simulation shows that the waves at the equatorial stratosphere, which are known to drive this climate mode, can originate far away from the equator in the troposphere. The obliquely propagating waves toward the equator are found to play a huge role in the phase progression of the quasi-biennial oscillation as well as in its penetration into the lower stratosphere. Such waves will require further attention, given that current climate models are struggling to simulate the quasi-biennial oscillation down to the lower stratosphere to reproduce its observed impacts on the surface climate.

Young-Ha Kim et al.

Status: open (until 29 Dec 2023)

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  • CC1: 'SAO vs QBO comment on egusphere-2023-2663', Paul PUKITE, 23 Nov 2023 reply

Young-Ha Kim et al.

Young-Ha Kim et al.


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Short summary
The quasi-biennial oscillation, which governs the tropical stratospheric circulation, is driven mainly by small-scale wave processes. We employ a novel method to realistically represent the wave processes in a global model, thereby revealing an aspect of the oscillation that could not be identified before. We found that oblique propagation of waves, a process that existing climate models cannot account for, plays a pivotal role in the stratospheric circulation and its oscillation.