Abstract: In this paper, a "critical perturbation" method is used to study the physical structure of mesoscale symmetric disturbance systems which are far from the equilibrium atmospheric state. The results show that disturbance systems will be in a state far from their equilibrium state if put under the condition of supercritical bifurcation, leading to strong development of the disturbance. The structure is generally consistent with the composite study of tropical cloud clusters by Williams and Gray (1973).