Influence of the Southern Hemisphere Circulations on the Active-Break Cycle of the Indian Summer Monsoon

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During the northerm summer monsoon period, the cloudiness fluctuation over and around India shows a predominant periodicity of 30 to 40 days as a major active-break cycle of monsoon activity, and this fluctuation appears as a northward phase shift of maximum (or minimum) cloudiness from the equatorial Indian Ocean toward the Himalayas (T. YASUNARI : J. Meteorol. Soc. Jpn, 57,227,1979; ibid., 58,225,1980). It has also been revealed that the northward movement of the cloudiness with this periodicity is triggered by the cold air outbreak toward the equator, associated with the large-scale westerly wave motions such as an index cycle in the Southern Hemisphere mid-latitudes (T. YASUNARI : J. Meteorol. Soc. Jpn, 59,336,1981). In addition, the analysis of the temperature fluctuation at 500mb over Syowa Station, East Antarctica, showed the dominant periodicity of the same period range (30-40 days) especially in the winter season. These results lead to a tentative idea that the major active-break cycle of Asian summer monsoon is closely linked with the hemispheric-scale wave motions in the Southern Hemisphere including the circumpolar vortex over Antarctica.
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