The simulation of the Madden–Julian Oscillation (MJO) and convectively coupled equatorial waves (CCEWs) is considered in 13 state-of-the-art models from phase 6 of the Coupled Model Intercomparison Project (CMIP6). We use frequency–wavenumber power spectra of the models and observations for Outgoing Longwave Radiation (OLR) and zonal winds at 250 hPa (U250), and consider the historical simulations and end of twenty-first century projections for the SSP245 and SSP585 scenarios. The models simulate a spectrum quantitatively resembling that observed, though systematic biases exist. MJO and Kelvin waves (KW) are mostly underestimated, while equatorial Rossby waves (ER) are overestimated. Most models project a future increase in power spectra for the MJO, while nearly all project a robust increase for KW and weaker power values for most other wavenumber–frequency combinations, including higher wavenumber ER. In addition to strengthening, KW also shift toward higher phase speeds (or equivalent depths). Models with a more realistic MJO in their control climate tend to simulate a stronger future intensification.
Bibliographical noteFunding Information:
C. I. G. and H. B. are supported by the ISF-NSFC joint research program (Grant No. 3259/19) and by the European Research Council starting grant under the European Union’s Horizon 2020 research and innovation program (Grant Agreement 677756). J. R. is supported by the National Natural Science Foundation of China (42175069). The authors have no competing interests to declare that are relevant to the content of this article.
Interpolated OLR data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/data/gridded/data.interp_OLR.html. CMIP6 data is available from the ESGF website at https://esgf-node.llnl.gov/projects/cmip6/. The authors thank Paul Roundy and the two anonymous reviewers for their constructive comments.
© 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
- Convectively coupled equatorial waves
- Kelvin waves
- Madden–Julian Oscillation
- Tropical spectrum