Strengthening Causal Connections Between the MJO and the North Atlantic in Future Climate Projections

Abstract:

Whilst the Madden Julian Oscillation (MJO) is well known to have an influence on midlatitude circulation and its predictability in the subseasonal-to-seasonal (S2S) timescales, little is known about the expected behavior of these teleconnections under anthropogenic warming. This study investigates MJO related teleconnections, the causal pathways of these connections (i.e., as tropospheric or stratospheric), and their changes, focusing primarily on impacts on the North Atlantic Oscillation (NAO) in boreal winter. Here we utilize data from the historical and SSP585 climate change projections of the CESM2 coupled climate model along with several novel data-driven approaches, namely the STRIPES (Sensitivity to the Remote Influence of Periodic EventS) index (Jenny et al. 2019) and graphical causal models. These approaches collectively indicate that the MJO’s influence on the North Atlantic strengthens in the future, which appears to be consistent with an extended North Pacific jet as discussed in Zhou et al. (2020). In addition, the graphical causal model approach allows us to distinguish the causal wave propagation pathways associated with the teleconnections. While the study shows that both the stratospheric and tropospheric pathways connect the MJO to the North Atlantic, it suggests that the strengthening of the MJO-NAO causal connection in the 21st century is due exclusively to the tropospheric pathway.

References:

• Jenney, A. M., Randall, D. A., & Barnes, E. A. (2019). Quantifying regional sensitivities to periodic events: Application to the MJO. Journal of Geophysical Research: Atmospheres, 124, 3671– 3683. https://doi.org/10.1029/2018JD029457
• Zhou, W., Yang, D., Xie, S., & Ma, J. (2020). Amplified Madden–Julian oscillation impacts in the Pacific–North America region. Nat. Clim. Chang. 10, 654–660. https://doi.org/10.1038/s41558-020-0814-0