Development of convection along the SPCZ within a Madden-Julian oscillation

A subtropical Rossby-wave propagation mechanism is proposed to account for the poleward and eastward progression of intraseasonal convective anomalies along the South Pacific convergence zone (SPCZ) that is ob-served in a significant proportion of Madden-Julian oscillations (UrOs). Large-scale convection, associated with an MJO, is assumed to be already established over the Indonesian region. The latent heating associated with this convection forces an equatorial Rossby-wave response with an upper-tropospheric anticyclone centred over, or slightly to the west of, the convection. Large potential-vorticity (PV) gradients, associated with the subtropical jet and the tropopause, lie just poleward of the anticyclone, and large magnitude PV air is advected equatorwards on the eastern side of the anticyclone. This 'high ' PV air, or upper-tropospheric trough, is far enough off the equator that it has associated strong horizontal temperature gradients, and it induces deep ascent on its eastern side, at a latitude of about 15-30". If this deep ascent is over a region susceptible to deep convection, such as the SPCZ