Drivers of uncertainty in future projections of Madden–Julian Oscillation teleconnections

Abstract

Abstract. Teleconnections from the Madden–Julian Oscillation (MJO) are a key source of predictability of weather on the extended timescale of about 10–40 d. The MJO teleconnection is sensitive to a number of factors, including the mean dry static stability, the mean flow, and the propagation and intensity characteristics of the MJO, which are traditionally difficult to separate across models. Each of these factors may evolve in response to increasing greenhouse gas emissions, which will impact MJO teleconnections and potentially impact predictability on extended timescales. Current state-of-the-art climate models do not agree on how MJO teleconnections over central and eastern North America will change in a future climate. Here, we use results from the Coupled Model Intercomparison Project Phase 6 (CMIP6) historical and SSP585 experiments in concert with a linear baroclinic model (LBM) to separate and investigate alternate mechanisms explaining why and how boreal winter (January) MJO teleconnections over the North Pacific and North America may change in a future climate and to identify key sources of inter-model uncertainty. LBM simulations suggest that a weakening teleconnection due to increases in tropical dry static stability alone is robust across CMIP6 models and that uncertainty in mean state winds is a key driver of uncertainty in future MJO teleconnections. Uncertainty in future changes to the MJO's intensity, eastward propagation speed, zonal wavenumber, and eastward propagation extent are other important sources of uncertainty in future MJO teleconnections. We find no systematic relationship between future changes in the Rossby wave source and the MJO teleconnection or between changes to the zonal wind or stationary Rossby wave number and the MJO teleconnection over the North Pacific and North America. LBM simulations suggest a reduction of the boreal winter MJO teleconnection over the North Pacific and an uncertain change over North America, with large spread over both regions that lends to weak confidence in the overall outlook. While quantitatively determining the relative importance of MJO versus mean state uncertainties in determining future teleconnections remains a challenge, the LBM simulations suggest that uncertainty in the mean state winds is a larger contributor to the uncertainty in future projections of the MJO teleconnection than the MJO.

Quantifying the Effect of Climate Change on Midlatitude Subseasonal Prediction Skill Provided by the Tropics

“…Our results are supported by recent research on changes to MJO and ENSO teleconnections. In particular, the increase in skill along the west coast of North America is consistent with the projected eastward shift of MJO and ENSO teleconnections in the future (e.g., Beverley et al., 2021; Fredriksen et al., 2020; Jenney et al., 2021; J. Wang et al., 2022). In addition, our results suggest there is a contribution from both subseasonal and seasonal variability changes to the increase in prediction skill in the North Atlantic.…”

“…Our results are supported by recent research on changes to MJO and ENSO teleconnections. In particular, the increase in skill along the west coast of North America is consistent with the projected eastward shift of MJO and ENSO teleconnections in the future (e.g., Beverley et al, 2021;Fredriksen et al, 2020;Jenney et al, 2021;J. Wang et al, 2022).…”

Effect of the Quasi‐Biennial Oscillation on the Madden Julian Oscillation Teleconnections in the Southern Hemisphere

“…The background flow during QBOW may be more conducive to wave propagation than for QBOE as under QBOW the zonal flow is displaced poleward, whereas for QBOE it is displaced equatorward (e.g., Elsbury et al., 2021). Differences in the basic state zonal flow have been suggested as influencing the position of the MJO teleconnections in the Northern Hemisphere (e.g., Jenney et al., 2021; Toms et al., 2020). In our experiments, there are significant differences in the zonal wind at 200 hPa, depending on the QBO phase in the AMIP‐TROP experiments as seen in Figure S8 in Supporting Information .…”

Projected future changes in equatorial wave spectrum in CMIP6

“…Exploring this possibility is left for future work, and in particular we note the recent study of Jenney et al (2021) who find that changes in the subtropical mean state may be more important than changes in the MJO itself for future changes in MJO teleconnections.…”