On the Relationship between the Madden-Julian Oscillation and the Hadley and Walker Circulations

This study investigates: (i) how the local meridional (Hadley) and zonal (Walker) circulations change in each phase of the Madden-Julian Oscillation (MJO); (ii) the effect of the propagation of the envelope of enhanced and suppressed convection on the poleward extent of the local Hadley circulations and, thus, the strengths and positions of the midlatitude jets; and (iii) the effect of the El Nino Southern Oscillation (ENSO) on the local Hadley and Walker circulations in each MJO phase. We examine these effects in the ERA-Interim by objectively decomposing the three-dimensional vertical mass flux into a zonal and meridional component, which allows us to investigate regional overturning circulations. We show that as the envelope of enhanced convection moves eastwards from Africa to the Central Pacific the local Hadley circulation is enhanced. The local Walker circulation is enhanced in region of enhanced convection and weakened in regions of suppressed convection. Midlatitude wave trains emanate from the region of either enhanced or suppressed convection over the Maritime Continent with the strongest wave pattern occurring in the winter hemisphere. The midlatitude jet is strengthened in regions of anomalous upper-level divergence due to enhanced convection and is weakened in regions of anomalous upper-level divergence. The analysis of the response of the local Hadley and Walker circulations in different phases of ENSO and the MJO suggests that the combined response is a linear combination of both phenomena.