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); and (ii) the effect of enhanced and suppressed MJO-related convection on the poleward extent of the local Hadley circulations and, thus, the strengths and positions of the subtropical jets. We examine these effects in ERA-Interim reanalysis by decomposing the vertical mass flux into zonal and meridional components. We show for the first time, that as the envelope of enhanced convection moves eastwards from Africa to the Central Pacific the local Hadley circulation is enhanced. The regional Walker circulation in the Pacific is strengthened when the envelope of active MJO convection is located over the Maritime Continent and weakened when the region of suppressed convection is located there. In regions of anomalous upper-level divergence the subtropical jet is enhanced. The core of the subtropical jet over Asia shifts eastwards with the progression of the MJO and shifts farther poleward in regions of anomalous upper-level divergence linked with enhanced convection. The region of either enhanced or suppressed convection over the Maritime Continent strengthens or weakens the local Hadley circulation, producing disturbances in the subtropical jet. These disturbances then force midlatitude Rossby waves that propagate across the Pacific Ocean in both hemispheres.