18th Conference on Climate Variability and Change


Relative cooling of the N. Indian Ocean: Its relation to aerosols and Indian/sub-Saharan Africa rainfall trends

C. E. Chung, SIO/Univ. of California, La Jolla, CA; and V. Ramanathan

Sea surface temperatures (SSTs) in the equatorial Indian Ocean (EIO) have warmed by about 0.6 to 0.8 K during the last 50 years accompanied by very little warming or even a slight cooling trend over the N. Indian Ocean (NIO) . This relative cooling of the NIO has resulted in a dramatic weakening of the north-south SST gradient in summer, to the extent that the gradient has nearly vanished in the recent years. Experiments with an atmospheric-general circulation model (A_GCM) reveal that the negative trend in the NIO_SST gradient has weakened the summer monsoonal circulation with less monsoon rainfall over India and excess rainfall in sub-Saharan Africa. Coupled ocean-atmosphere GCM (OA_GCM) simulations suggest that while greenhouse gas forcing is the major contributing factor for the equatorial warming, surface cooling due to manmade aerosols have masked the greenhouse warming in the NIO, thus weakening the SST gradient. The results here imply that the sooty aerosols have contributed to the poor Indian monsoon, while preventing the sub-Saharan region from becoming too dry. .

Session 9, Climate Model Analysis and Improvement
Thursday, 2 February 2006, 11:00 AM-4:30 PM, A314

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