  A dynamic equation for a large scale convective event in the tropical
atmosphere similar to the Madden--Julian Oscillation (MJO) is suggested based
on the meridional vorticity equation with buoyancy parametrized by Convective
Available Potential Energy (CAPE). The propagation is determined by the
nonlinear Burgers equation with a stationary solution describing a kink moving
towards the moisture source. In this conceptual model, the propagation speed
depends on the asymmetry in the zonal surface winds which is observed in the
boundary layer in the vicinity of an MJO event and attributed to Rossby and
Kelvin waves. Furthermore, the model predicts convection at the equator in the
east of the MJO which is not correlated with Kelvin and Rossby waves.
