Sensitivity of simulated MJO to model vertical resolution in GAMIL3

The impact of model vertical resolutions on simulation of the Madden–Julian Oscillation (MJO) was investigated using five AMIP simulations by the Grid-point Atmospheric Model of IAP LASG, version 3 (GAMIL3) with different vertical layers. Results showed that higher vertical resolutions produce a stronger and superior eastward propagation, coupled circulation–convection relationship, and MJO strength, as well as other convectively coupled equatorial waves when compared to the lowest vertical resolution. The improvements may be related to a better description of the tropical circulation in the higher vertical resolutions and model top, albeit without the significant improvement of MJO convection and stratospheric quasi-biennial oscillation in all simulations. Among the four tested high resolutions, the simulations with higher vertical resolutions from the surface to about 850 hPa produced better eastward propagation and larger total explained variance of the MJO, indicating the importance of the lower troposphere in simulating the MJO.