The annual cycle and interannual variability in the tropical Pacific and Indian Ocean regions.

Abstract

The annual cycle of outgoing longwave radiation (OLR), clouds, precipitation and sea level pressure is studied from satellite and station data in the tropical Indian and Pacific sectors. A region of heavy convection, termed the tropical convective maximum, moves from N to S and W to E in the Indian and Pacific sectors as the mean annual cycle proceeds from N summer to N winter. To study interannual fluctuations of the annual cycle in these regions, Indian monsoon rainfall is chosen as an indicator of precipitation and convection in the summer monsoon region. The dynamically coupled ocean-atmosphere system in the Indian-Pacific region is involved with producing Southern Oscillation-type signals in atmosphere and ocean in these sets of years, with extremes in the system being manifested as Warm and Cold Events. This is associated with the alternate strengthening and weakening of the mean W-to-E exchange of mass from the Indian to Pacific sectors in the atmosphere, and the interactive response of the ocean in helping reinforce and maintain those anomalies. These results point out that processes in the Indian-Pacific region are continually evolving from one annual cycle to the next and that Warm and Cold Events are not discrete occurrences but are extremes of patterns which appear in many other years as part of the dynamically coupled air-sea system in this region.-from Author