The Madden Julian Oscillation is the dominant intraseasonal signal in rainfall and atmospheric circulation in the tropics. Characteristics of the MJO have been difficult to explain, and consensus has been difficult to reach on its most fundamental dynamics. This presentation will illustrate the complexity of the basic dynamics of the atmospheric circulation patterns associated with the MJO. MJO convection tends to move eastward at roughly 1-9 ms^-1, and its spatial scales vary across the population of events. Further, the structure of its associated global atmospheric circulation patterns varies with the phase speed. The phase speed of the MJO might be regulated by many different factors. Previous works have suggested that moist processes govern the phase speed. Yet, convection and rainfall tend to be less intense in MJO events propagating more slowly than 5 ms⁻¹ than for MJO events moving at around 5 ms⁻¹. Analysis suggests dynamical feedbacks that might influence MJO phase speed associated with Rossby wave breaking and blocking. A real-valued wavelet filter is applied to extract time series characterized by selected zonal wavenumbers and frequencies at select equatorial base longitudes, and linear regression is applied to identify the associated circulation structures at different phase speeds. Surprisingly, results show that blocking tends to occur east of fast events and west of slow events. Examination of terms in the momentum budget suggests that blocking dynamics dominate over forcing from convection in determining the phase speed and the circulation structures observed in the slowest events.