Annual Cycle in Rainfall of the Indo–Pacific Region

Abstract

Rainfall is analyzed for the Indian and west Pacific Oceans. The analysis uses a multichannel scheme to retrieve open-ocean rain rate from brightness temperatures measured between 1979 and 1986 by the Nimbus-7 Scanning Multichannel Microwave Radiometer. Rain rates were averaged over calendar months for 1° boxes. These rain rates were checked against two published climatologies. They were analyzed in light of historical climatologies of rainfall over the Indian and west Pacific Oceans. Except for the Somali jet, the scheme adequately represented ambient conditions over the Indian and west Pacific Oceans. Rain tended to fall in two bands paired across the equator. Over the Indian Ocean, the southern member consistently dominated the northern member. Over the west Pacific Ocean, at times through the course of the year, each member dominated the other. Close to the East Indies northern and southern members merged. Bands were modulated by a pair of wavelike conglomerates. Following the sun, each wave conglomerate strengthened on the poleward legs of its track and weakened on the equatorward legs. One wave conglomerate appeared to follow a clockwise loop connecting waters near Madagascar with the Arabian Sea, India, and the Bay of Bengal. The other appeared to follow a counterclockwise loop connecting Austral?Melanesian waters with the Philippine Sea, the South China Sea, and the Bay of Bengal. Converging in boreal spring on northbound legs, the wave conglomerates appeared to merge over South Asia.