Impact of Air–Sea Coupling on MJO Simulation

The MJO (Madden–Julian Oscillation) simulation ability of the numerical experiments from CNRM GCMs (General Circulation Models) participated in the MJOTF/GASS (MJO Task Force/Global Energy and Water Cycle Experiment Atmospheric System Study) project was evaluated by tracking the eastward propagating positive equatorial precipitation anomalies. The GCMs included a fully coupled simulation (CNRM-CM), a half-coupled simulation (CNRM-ACM), and an uncoupled simulation (CNRM-AM) based on 1991–2010 data. The possible impacts of air–sea coupling on the MJO simulation were investigated. The CNRM-CM showed the highest ability in simulating the MJO characteristics, in terms of the occurrence frequency, amplitude, and propagation range. The climatological sea surface temperature (SST) of the CNRM-CM and CNRM-ACM showed a distinct cold bias over the Indo–Pacific warm pool region, compared with that of the CNRM-AM. The cold bias did not strongly impact the MJO simulation ability compared with the impacts on the MJO simulation abilities of the CNRM-ACM and CNRM-AM. The zonal gradient of the intraseasonal SST was significant in the CNRM-CM, with a strong positive intraseasonal SST anomaly to the east of the MJO convection center and a negative intraseasonal SST anomaly to the west of the MJO convection center when the MJO was over the Indian Ocean. In contrast, such a gradient was lost in the CNRM-ACM and CNRM-AM. The results indicate that the impact of the air–sea coupling on the MJO simulations by the CNRM GCMs was mainly through the influences on the intraseasonal SST variability.