Abstract
The seasonal and the intraseasonal behaviors of the deep convective clouds are investigated by using the activity index devised in Part I of this paper. The monthly mean distributions for the period from May through August 1979 have revealed many seasonal characteristics which have been inferred in the past from the cloudiness or from the outgoing longwave radiation (OLR). The latitudinal change of the distribution has clearly shown the northward advance of the convective area over the Southeast Asia, the formation of the highly convective area which brings the Bai-u (Mei-yu in Chinese) rain, and the northward shift of the convective belt associated with ITCZ over the western Pacific.
The latitude-time section of the above activity has revealed the existence of the major intraseasonal variation with the 30- to 40-day periodicity. Over the Indo-China peninsula and the Bay of Bengal, it appears in the form of the repetitive progressions from the equatorial South Indian Ocean. The more detailed analysis using the band-pass filter has revealed that there also exists a southward-progressing component which comes down from the Tibetan Plateau. Moreover, it turned out that the similar situation also occurs over the western Pacific. The composite analysis performed on the wind variation at 850mb level verified that the above 30- to 40-day variation is associated with the active/break cycle of the Indian monsoon. When the monsoon westerly is most intensified over India, the enhanced deep convection appears over the region ranging from the northeastern India to the Philippines. In contrast, the suppressed condition appears over the equatorial Indian Ocean and the Tibetan Plateau. Furthermore, it turned out that the convective activity associated with ITCZ is also intensified at this stage over the tropical western Pacific.
