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climate change
climate variability
orbital forcing
ocean impact
Asian summer monsoon
simulation
MODELING INTERCOMPARISON PROJECT
GENERAL-CIRCULATION MODEL
LAST
GLACIAL MAXIMUM
AFRICAN MONSOON
ATMOSPHERIC CIRCULATION
INTERANNUAL
VARIABILITY
GLOBAL MONSOONS
MIDDLE HOLOCENE
CLIMATE
MIDHOLOCENE
Abstract:
The importance of orbital forcing and ocean impact on the Asian summer monsoon in the Holocene is investigated by comparing simulations with a fully coupled ocean-atmosphere general circulation model (FOAM) and with the atmospheric component of this model (FSSTAM) forced with prescribed modem sea-surface temperatures (SSTs). The results show: (1) the ocean amplifies the orbitally-induced increase in African monsoon precipitation, makes somewhat increase in southern India and damps the increase over the southeastern China. (2) The ocean could change the spatial distribution and local intensity of the orbitally-induced latitudinal atmospheric oscillation over the southeastern China and the subtropical western Pacific Ocean. (3) The orbital forcing mostly enhances the Asian summer precipitation in the FOAM and FSSTAM simulations. However, the ocean reduces the orbitally-induced summer precipitation and postpones the time of summer monsoon onset over the Asian monsoon region. (4) The orbital forcing considerably enhances the intensity of upper divergence, which is amplified by ocean further, over the eastern hemisphere. But the divergence is weaker in the FOAM simulations than in the FSSTAM simulations when the orbital forcing is fixed. (5) The orbital forcing can enhance the amplitude of precipitation variability over the subtropical Africa, the southeastern China and northwestern China, inversely, reduce it over central India and North China in the FOAM and FSSTAM simulations. The ocean obviously reduces the amplitude of precipitation variability over most of the Asian monsoon regions in the fixed orbital forcing simulations. (6) The areas characterized by increased summer precipitation in the long-term mean are mostly characterized by increased amplitude of short-term variability, whereas regions characterized by decreased precipitation are primarily characterized by decreased amplitude of short-term variability. However, the influences of orbital forcing or dynamical ocean on regional climate depend on the model. Crown Copyright (c) 2007 Published by Elsevier B.V. All rights reserved.
