Detailed features of heavy rainfalls in three medium-scale disturbances developed in Baiu front over the southwestern Japan Islands have been studied basing on time series of 10-min rainfall amounts and 3-radar PPI composite photographs. For rainfall analysis, the rainfalls were classified into two categories, continuous and convective rains, according to intensity fluctuation and intensity threshold (2mm/10min).Results revealed that the wave-shaped echo system associated with one medium-scale disturbance consists of thin weak widespread echo in the front and in the north of the disturbance and of convective echo cells distributed around the crest or the trailing portion of the wave. The convective echo cells are mostly organized into mesoscale echo clusters arranged with 100-150km spacing.Results also revealed that the wave-shaped medium-scale rainfall system consists of two specified areas. The one characterized by continuous rain spreads to north and east of the wave crest, corresponding to thin weak widespread echo area. The other characterized by convective rain is the heavy rainfall zone in the crest or the trailing portion of the wave, corresponding to the areas of convective echoes organized into mesoscale cluster.Applying spectral analysis method to time series of 10-min rainfall amounts, it isconfirmed objectively that the rainfalls in the heavy rainfall zone are due to mesoscale pulsations of convective rain.The stratification over the convective rain area is evidently different from that over the continuous rain area, i.e., the lower layer is unstable in the convective rain area (southern convective echo area), while stable in the continuous rain area (northern thin weak widespread echo area).
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