The role of ocean thermodynamics and dynamics in Asian summer monsoon changes during the mid-Holocene
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.
KeywordsIndian Ocean Asian Monsoon Precipitation Change Ocean Dynamic Ocean Coupling
We thank Tomonori Segawa for running simulations and help with the analysis tools. We also thank Takashi Sakamoto, Julia C. Hargreaves, Kotaro Sakai, Shigenori Murakami, and the staff of FRCGC/JAMSTEC for their support and helpful discussions. The MIROC development team is appreciated for their valuable endeavour. The anonymous reviewers are greatly thanked for their constructive comments to improve the manuscript. The model simulations were performed on the Earth Simulator at JAMSTEC. This work was partially supported by the Project for Sustainable Coexistence of Humans, Nature and Earth promoted by the Ministry of Education, Culture, Sports, Science and Technology of Japan, and by JSPS Grant-in-Aid for Scientific Research (B) no. 16340136.
- Joussaume S, Taylor KE, Braconnot P, Mitchell JFB, Kutzbach JE, Harrison SP, Prentice IC, Broccoli AJ, Abe-Ouchi A, Bartlein PJ, Bonfils C, Dong B, Guiot J, Herterich K, Hewitt CD, Jolly D, Kim JW, Kislov A, Kitoh A, Loutre MF, Masson V, McAvaney B, McFarlane N, de Noblet N, Peltier WR, Peterschmitt JY, Pollard D, Rind D, Royer JF, Schlesinger ME, Syktus J, Thompson S, Valdes P, Vettoretti G, Webb RS, Wyputta U (1999) Monsoon changes for 6000 years ago: Results of 18 simulations from the Paleoclimate Modeling Intercomparison Project (PMIP). Geophys Res Lett 26(7):859–862CrossRefGoogle Scholar
- K-1 model developers (2004) K-1 coupled model (MIROC) description. K-1 technical report, 1. In: Hasumi H, Emori S (eds) Center for climate system research, University of Tokyo, Japan, p 34Google Scholar