Zonal‐Scale of the Madden‐Julian Oscillation and Its Propagation Speed on the Interannual Time‐Scale

While no significant long-term trend in the propagation speed of Madden-Julian Oscillation (MJO) boreal winter is found during past decades, pronounced year-to-year variability MJO phase illustrated by analyzing a century-long record data set. During winters when fast observed, exhibits much larger zonal-scale than that with slow propagation. A broader extension circulation effectively induces stronger and lower-tropospheric moistening (drying) to east (west) through horizontal moisture advection, prompting faster speed. The coincident anomalously increased background sea surface temperatures precipitable water over both western Indian Ocean central/eastern Pacific, reminiscent an expansion Indo-Pacific warm pool. fundamental question remains open regarding key processes determine organization.