Infrared radiance measurements at cloud top by the Japanese Geostationary Meteorological Satellite (GMS) were used to study the structure and propagation of tropical convective systems over the equatorial western Pacific. Results indicate that tropical convection in this region possesses three fundamental periodicities: 1 day, 2--3 days, and 10--15 days. Cloud clusters within these convective systems interact to produce a hierarchy of collective motions covering all of these three basic time scales. The 10- to 15-day time scale is closely related to the intraseasonal (or 30--60 day) oscillations that propagate from the Indian Ocean to the western Pacific along the equator all year round. Large convective complexes known as supercloud clusters (SCC) are found to organize in the 10- to 15-day time scale, especially over the open, warm water of the western/central Pacific (160¿E to 180¿). The SCCs generally propagate eastward, although occasionally they can also propagate westward. The zonal propagation can occur either continuously or intermittently. In both cases the SCC is found to be made up of several well-organized cloud clusters, which are generated at 2- to 3-day intervals and propagate in the opposite direction ot the SCC.

The diurnal variation is most pronounced over the maritime continent, although significant amplitudes are also found over the open ocean. The amplitude of the diurnal cycle is strongly modulated by the 2- to 3-day and 10- to 15-day oscillations. Advanced spectral analysis methods applied to convective indices derived from the radiance data confirm this hierarchical structure in cloud clusters in the ropical western Pacific. In addition to the embedding of well-organized clusters within a SCC in the spatial domain, there is also a similar embedding by successive longer scales in the time domain. Interactions between the major frequency groups appear also to give rise to intermediate frequency variations. A discussion of the present results in the context of equatorial wave dynamics of the moist tropical atmosphere is also presented. ¿1991 American Geophysical Union