Relationships Between the Eastward Propagation of the Madden‐Julian Oscillation and its Circulation Structure

The circulation associated with convection of the Madden-Julian Oscillation (MJO) has been suggested to have an impact on its propagation by a number of previous studies. This circulation contains both flanking Rossby waves to the rear and a Kelvin wave leading the convective center. In this study, individual MJO convective envelopes from a 40-year database are tracked, a technique to scale the MJO by its zonal wavelength is employed, and statistical methods are used to assess how the MJO circulation pattern might impact its eastward propagation downstream. Results suggest that continuous eastward propagation of the MJO is favored when a strong Kelvin wave circulation is present east of MJO convection, indicated by both an easterly zonal wind anomaly and negative geopotential height anomaly. In addition to the known significance of having Kelvin wave easterly wind anomalies, the results of this study highlight that the existence of negative geopotential height is important to supporting moistening and MJO propagation. It is found that importance of the Kelvin wave signal to MJO propagation depends on the region that the MJO is located over. Kelvin wave circulation east of MJO convection enhances moistening to support continuous eastward propagation of the MJO, mainly through meridional moisture advection due to the coupling between the Kelvin wave and Rossby-like disturbances east of the active convection. The roles of boundary layer convergence and vertical moistening are also discussed.