Relative Roles of Circumnavigating Waves and Extratropics on the MJO and Tropical Mean State

A set of atmospheric GCM experiments is designed to explore the relative roles of the circumnavigating waves and the extratropics on the MJO. In a ‘control' simulation, the model is forced by the climatological monthly sea surface temperature for 20 years. In the first sensitivity experiment, the model prognostic variables are relaxed in the tropical Atlantic region (80°W-0°, 20°S-20°N) toward the ‘controlled' climatological annual cycle to suppress the influences from the circumnavigating waves. In the second sensitivity experiment, the model prognostic variables are relaxed in the 20°-30° latitude zones toward the ‘controlled' climatological annual cycle to suppress the influences from the extratropics or the tropics-extratropics interactions. The numerical results demonstrate that the extratropics play a more important role in maintaining the MJO variance than the circumnavigating waves. The simulations further show that both the tropical mean precipitation and the intraseasonal precipitation variability are reduced when the extratropical influences are suppressed. The interactions between the mean state and the MJO is further explored by conducting a moisture budget analysis. This study is the first attempt to quantitatively separate the effects of the circumnavigating waves and the extratropics on the MJO. Implications and limitations of the present study will be discussed in the meeting.