The dynamical features of air-sea coupling waves and their stabilities in a simple coupled air-sea model in the tropics have been studied with respect to interaction occurring among different types of the free waves in the ocean and in the atmosphere.It is pointed out that there exist a stable and an unstable air-sea interaction modes in the tropical coupled system, respectively.The propagation of the unstable mode relies greatly on the zonal space scale, i.e.only for wave length ranging from 5 000 km to 10 000 km can the disturbance unstably move slowly eastward.The waves that slowly propagate unstably eastward agree well with the observational facts.Finally,it is also proposed that the interaction between Kelvin wave in one medium and Rossby wave in another medium is a necessary condition for the occurrence of destabilization of the coupled air-sea system in the tropics.
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