The Kelvin wave-CISK theory of the Madden-Julian oscillations in the tropical troposphere is reexamined by introducing a phase lag between the maximum cloud heating and the maximum convergence of the Kelvin wave. The study was motivated by the observations in the equatorial Pacific that clouds in the Kelvin waves are organized into westward propagating mesoscale cloud clusters. Since this phase lag depends on the propagation speed of the Kelvin waves, the waves become dispersive, and this leads to a favored growth of long waves. The results of this study suggest that the presence of organized mesoscale cloud systems needs to be parameterized directly into those climate models that cannot adequately describe their dynamics.
