The role of ocean thermodynamics and dynamics in Asian summer monsoon changes during the mid-Holocene |
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Authors: | R Ohgaito A Abe-Ouchi |
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Institution: | (1) Frontier Research Center for Global Change, JAMSTEC, Yokohama 236-0001, Japan;(2) Center for Climate System Research, The University of Tokyo, Kashiwa 277-8568, Japan |
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Abstract: | Studies of climate change 6,000 years before present using atmospheric general circulation models (AGCMs) suggest the enhancement
and northward shift of the summer Asian and African monsoons in the Northern Hemisphere. Although enhancement of the African
monsoonal precipitation by ocean coupling is a common and robust feature, contradictions exist between analyses of the role
of the ocean in the strength of the Asian monsoon. We investigated the role of the ocean in the Asian monsoon and sought to
clarify which oceanic mechanisms played an important role using three ocean coupling schemes: MIROC, an atmosphere–ocean coupled
general circulation model C]; an AGCM extracted from MIROC coupled with a mixed-layer ocean model M]; and the same AGCM,
but with prescribed sea surface temperatures A]. The effect of “ocean dynamics” is quantified through differences between
experiments C] and M]. The effect of “ocean thermodynamics” is quantified through differences between experiments M] and
A]. The precipitation change for the African and Asian monsoon area suggested that the ocean thermodynamics played an important
role. In particular, the enhancement of the Asian monsoonal precipitation was most vigorous in the AGCM simulations, but mitigated
in early summer in ocean coupled cases, which were not significantly different from each other. The ocean feedbacks were not
significant for the precipitation change in late summer. On the other hand, in Africa, ocean thermodynamics contributed to
the further enhancement of the precipitation from spring to autumn, and the ocean dynamics had a modest impact in enhancing
precipitation in late summer. |
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Keywords: | |
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