Abstract
Interdecadal variations of precipitation over the tropical Pacific and Indian Oceans and their relationships with SST are investigated by using surface and satellite observation data. The analyses of surface precipitation indicated that the precipitation in the tropical central-eastern Pacific was increased during the period from the mid 1970s to the 1980s in accordance with the increase of SST in these regions. On the other hand, the precipitation in the tropical western Pacific was rather decreased during this period probably due to changes of tropical east-west circulations affected by the enhanced convection in the central-eastern Pacific. The precipitation in the South Indian Ocean was increased since the mid 1970s corresponding to the increase of SST over the Indian Ocean, but it was nearly constant in spite of gradual increase of SST before that period. Monthly mean high-cloud amount data derived from the GMS-IR observations during 16 years from April 1978 to February 1994 are analyzed to obtain long-term trend of the convective activity in the tropical western Pacific. The computation of the linear trend of the high-cloud amount for the 16 years reveals that decreasing trends dominate over most of the tropical western Pacific, but increasing trends can be seen in the equatorial central Pacific around the dateline. These results suggest that El Nino-like environmental conditions such as enhanced convection in the central Pacific, but suppressed convection in the western Pacific prevail over the tropical Pacific during recent decades. These findings are consistent with previous studies demonstrating that there occurred decadal scale changes in atmosphere-ocean systems in the tropical Pacific during the 1970s-1980s period. The results in this study support the scenario suggested by Nitta and Yamada (1989) that large atmospheric anomaly circulations in the North Pacific Ocean appeared in recent decades might be generated by the enhanced convective activity in the tropical central-eastern Pacific due to the increase of the tropical SST.
