The impact of subgrid-scale gravity waves on the Brewer-Dobson circulation

The Brewer-Dobson circulation (BDC) is a meridional circulation mainly driven through mean-flow forcing by Rossby-wave breaking that is, however, also influenced by gravity waves (GW). As some part of GW dynamics is subgrid-scale in numerical climate and weather prediction models, an appropriate wave parameterization and later an accurate separation of the drivers are necessary to understand the impact of the subgrid-scale GWs on the BDC.

Polichtchouk et al. (2018) explored the sensitivity of BDC to the parameterized GW drag by separating the drivers of the residual circulation using the downward-control principle. Even in relatively high-resolution simulations, the parameterized drags are found to significantly contribute to the BDC in the lower stratosphere, especially for northern hemisphere winter-pole downwelling.

We parameterize subgrid-scale GWs in the Lagrangian ray-tracing scheme Multi-Scale Gravity-Wave Model (MS-GWaM) (Bölöni et al. 2021; Kim et al. 2021). MS-GWaM includes interactions between the GW field and the resolved flow, which are neglected in the traditional GW parameterization schemes. It has been implemented successfully into of the Icosahedral Non-hydrostatic (ICON) model in its upper-atmosphere configuration. Using the MS-GWaM output, we diagnose the sensitivity of the BDC using the downward-control principle.