Distinct responses of East Asian and Indian summer monsoons to astronomical insolation during Marine Isotope Stages 5c and 5e

Loess and stalagmite records in China show different responses of Asian monsoon to the astronomical insolation during Marine Isotope Stage (MIS) 5c and 5e, raising the question whether the amplitudes of the whole Asian monsoon are linearly controlled by the astronomical summer insolation changes and whether the regional differences exist. In this study, a set of numerical experiments are conducted for these stages to examine the sensitivity of Asian summer monsoon to changes in the astronomical parameters. The results highlight a complicated response changing with regions and signals. The East Asian monsoon is remarkably stronger during MIS-5e, which is characterized by southerly winds, primarily due to the anomalous anticyclone over northwestern Pacific. The intensified East Asian monsoon leads to less precipitation in the eastern China and Japan but more in the further north and northwest. However, the Indian monsoon circulation does not vary significantly while the precipitation over Arabian Sea is significantly promoted by the upward air motion. Change in water vapor sources of Indian and Pacific Oceans qualitatively explains the observed differences in stalagmite δ¹⁸O records, implying that these proxy changes are primarily controlled by the water vapor delivery from oceans, at least on the astronomical timescale.