MJO Energy Budget Residuals in CMIP6: A Focus on Vertical Resolution

Abstract This study investigates the influence of model‐output vertical resolution on the Madden‐Julian Oscillation (MJO)‐related moist static energy (MSE) budget. Using reanalysis data at varying vertical resolutions (raw levels, six standard layers of CMIP6 daily output, fine upper‐tropospheric, and fine lower‐tropospheric), we demonstrate that limiting vertical levels to six leads to substantial budget residuals, mirroring those in CMIP6 daily output. Notably, enhanced upper‐tropospheric resolution captures moist processes more accurately compared with high resolution in the lower troposphere. These budget residuals, which amplify with rainfall anomalies, stem from overestimated vertical MSE advection driven by an unrealistically strong vertical gradient in mean‐state dry static energy (DSE) in the upper troposphere. Sensitivity tests further indicate that including an additional 150 hPa level in the six standard layers substantially reduces the background DSE bias and budget residuals. In CMIP6 models, unrealistic mean DSE gradients also appear in daily output rather than in finer‐resolution monthly output, leading to overestimated vertical MSE advection. These findings suggest that limited vertical resolution in CMIP6 daily output partially contributes to the observed MSE budget residuals.