The Sensitivity of the African-Asian Monsoonal Climate to Orbital Parameter Changes for 9000 Years B.P. in a Low-Resolution General Circulation Model

J. E. Kutzbach Center for Climatic Research and Department of Meteorology, University of Wisconsin. Madison 53706

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B. L. Otto-Bliesner Center for Climatic Research and Department of Meteorology, University of Wisconsin. Madison 53706

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Abstract

The earth's orbital parameters, precession, obliquity and eccentricity, produce solar radiation differences (compared to present) of ∼7% at the solstices 9000 years before present (B.P.): more radiation in June-July-August, less in December-January-February. When this amplified seasonal cycle of solar radiation is used to drive a low-resolution general circulation model, an intensified monsoon circulation is simulated for Northern Hemisphere summer. The annual- and global-average land surface temperature and the annual- and global-average precipitation are the same for the simulated 9000 years B.P. climate and the present climate. Certain features of the simulated monsoon climate from this orbital-parameter sensitivity experiment agree with the paleoclimatic evidence.

Abstract

The earth's orbital parameters, precession, obliquity and eccentricity, produce solar radiation differences (compared to present) of ∼7% at the solstices 9000 years before present (B.P.): more radiation in June-July-August, less in December-January-February. When this amplified seasonal cycle of solar radiation is used to drive a low-resolution general circulation model, an intensified monsoon circulation is simulated for Northern Hemisphere summer. The annual- and global-average land surface temperature and the annual- and global-average precipitation are the same for the simulated 9000 years B.P. climate and the present climate. Certain features of the simulated monsoon climate from this orbital-parameter sensitivity experiment agree with the paleoclimatic evidence.

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