Revisiting the Physical Mechanisms of East Asian Summer Monsoon Precipitation Changes During the Mid-Holocene: A Data–model Comparison

Abstract The mid-Holocene (MH; 6 ka) is one of the benchmark periods for the Paleoclimate Modeling Intercomparison Project (PMIP) and provides a unique opportunity to study monsoon dynamics and orbital forcing (i.e., mostly precession) that differ significantly from the present day. We conducted a data–model comparison along with a dynamic analysis to investigate monsoonal (i.e., East Asian summer monsoon; EASM) precipitation changes over East Asia during the MH. We used the three phases of the PMIP simulations for the MH, and quantitatively compared the model results with pollen-based climate records. The data–model comparison shows an overall increase in precipitation, except for a local decrease in EASM precipitation during the MH. Decomposition of the moisture budget into thermodynamic, dynamic components and co-variations in both allowed us to assess the relative role of thermodynamic and dynamic components in controlling EASM precipitation during the MH, and to investigate the precipitation changes obtained from pollen records in terms of physical processes. We show that the dynamic effect, rather than the thermodynamic effect, is the dominant control in increased EASM precipitation during the MH in both the proxy records and models. The dynamic increase in precipitation results mainly from the enhancement of horizontal monsoonal moisture transport that is caused by intensified stationary eddy horizontal circulation over East Asia. In addition, a cloud cooling effect reduced the thermodynamic contribution to the increase in EASM precipitation during the MH.