Preprints
https://doi.org/10.5194/wcd-2021-9
https://doi.org/10.5194/wcd-2021-9

  10 Feb 2021

10 Feb 2021

Review status: this preprint is currently under review for the journal WCD.

Mechanisms driving MJO teleconnection changes with warming in CMIP6

Andrea M. Jenney1, David A. Randall2, and Elizabeth A. Barnes2 Andrea M. Jenney et al.
  • 1Department of Earth System Science, University of California, Irvine, CA, USA
  • 2Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA

Abstract. Teleconnections from the Madden-Julian Oscillation (MJO) are a key source of predictability of weather on the extended time scale of about 10–40 days. The MJO teleconnection is sensitive to a number of factors, including the mean state dry static stability, the mean flow, and the propagation and intensity characteristics of the MJO itself, 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 potential predictability on extended time scales. Current state-of-the-art climate models do not agree on how MJO teleconnections 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 to separate and investigate alternate mechanisms explaining why and how MJO teleconnections over the North Pacific and North America will change in a future climate, and to identify key sources of inter-model uncertainty. We find that decreases to the MJO teleconnection due to increases in tropical dry static stability alone are robust, and that uncertainty in mean state winds are a key driver of uncertainty in future MJO teleconnections. We find no systematic relationship between changes in Rossby wave excitation and the MJO teleconnection. However, we find that models that predict increases (decreases) in the stationary Rossby wave number over the gulf of Alaska also predict stronger (weaker) teleconnections over North America. Uncertainty in future changes to the MJO's intensity, eastward propagation speed, and eastward propagation extent are other important sources of uncertainty in future MJO teleconnections, although to a lesser degree than uncertainty in the mean state. The overall outlook is a reduction of the boreal winter MJO teleconnection across the vast majority of CMIP6 models, especially over the North Pacific, but with some nuance over North America due to larger sensitivity to expansion of the MJO's eastward extent.

Andrea M. Jenney et al.

Status: open (until 24 Mar 2021)

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Andrea M. Jenney et al.

Data sets

Mechanisms driving MJO teleconnection changes with warming in CMIP6: Data for figures Andrea M. Jenney https://doi.org/10.5281/zenodo.4499184

Andrea M. Jenney et al.

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Short summary
Storm activity in the tropics is one of the key phenomena that provide weather predictability on extended time scale of about 10–40 days. The influence of tropical storminess on places like North America is sensitive to the overall average state of the climate system. In this study, we show that global warming will likely lead to decreases in the influence of these storms on weather over the North Pacific, but that there is a lot of uncertainty in how this influence will change.