MJO Simulation in CMIP6 Models: How Much Improvement Has Been Made from CMIP5 to CMIP6?

We evaluate the ability of climate models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) to simulate the Madden-Julian oscillation (MJO) and compare them with CMIP5 models. In the presentation, we will address the following two questions: 1) How much improvement has been made from CMIP5 to CMIP6 models in simulating the MJO?; 2) If there has been any robust improvement, which parameterized physical processes are responsible? The process-oriented MJO simulation diagnostics that focus on moisture-convection coupling, longwave radiation feedback, mean gross moist stability, and moisture mean state will be employed to address the second question. At the time of submitting this abstract, the Historical simulations of nine CMIP6 models have been analyzed. More models will be included as they become available in the CMIP6 archive.

Our preliminary results suggest that the eastward propagation of the MJO is improved in the CMIP6 models as compared to the CMIP5 models. For example, the East/West power ratio of equatorial precipitation is greater than 2 in more than 50% of the CMIP6 models (5 out of 9), while only less than 30% of CMIP5 models exhibit such skill (10 out of 37), which is about 2.6 in observations. We also examine the behavior of the MJO around the Indo-Pacific Maritime Continent (MC). Many of the nine CMIP6 models analyzed reasonably represent the southward detouring of the MJO over the MC. However, a majority of the CMIP5 and CMIP6 models still have difficulty in simulating the “vanguard” precipitation in the MC islands, implying a systematic bias in the interaction of convection in the MC islands with large-scale circulation anomalies.