Relative Influence of Extratropical Northern and Southern Hemisphere on the MJO

The MJO is influenced by extratropics among other factors such as internal dynamics. However, how the Northern (NH) and Southern Hemispheres (SH) influence the MJO in different seasons are not known. To explore the relative roles of NH and SH on the MJO structure and its propagation, a set of idealized AGCM experiments, using ECHAM4, is designed. The “control” simulation is forced by the climatological monthly sea surface temperature. To suppress the extratropical forcing from the NH (SH) named the N Exp (S Exp), model prognostic variables are relaxed in the 20-30 degree north (south) latitude zones. A third sensitivity test combines N and S experiments (NS Exp).

We document the MJO's horizontal and vertical structures and its propagation in different seasons under the above experiments using the matrix provided by the U.S. CLIVAR MJO Working Group. The results indicate that the SH has a more prominent role in influencing the MJO structure compared to the NH. The relative influences will be further quantified by moisture and momentum budget analysis over different seasons. The limitations and implications of the results will be discussed.