Projected Future Changes in Equatorial Wave-modes in CMIP6

The simulation of the MaddenJulian Oscillation (MJO) and convectively coupled equatorial waves 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 velocity at 250 mbar (u250), and consider the historical and end-of-century conditions for the SSP245 and SSP585 scenarios. The models simulate a spectrum quantitatively resembling that observed, though systematic biases exist: the OLR low frequency variance is too strong while higher frequencies are too weak. A noticeable exception occurs in low frequencies and low positive wavenumbers: some models do not seem to have bias for MJO, while the others present lower variance than observations. The models project a future increase in power for the MaddenJulian oscillation (MJO) and Kelvin waves, and weaker power values for other wavenumber-frequency combinations. Models with a smaller bias in their historical simulation of the MJO tend to simulate a larger increase in MJO power, and models with a smaller bias in their historical simulation of the Kelvin wave tend to simulate a small increase in Kelvin power.