Abstract
This study investigates the response of large-scale atmospheric circulation over the Asian-Pacific sector and precipitation over eastern China to transient orbital changes during the Holocene summer using an intermediate-complexity climate model. Corresponding to variations in the incoming solar radiation, the eddy sea level pressure (SLP) exhibited an out-of-phase relationship between the North Pacific and the Eurasian landmass that was similar to the present-day Asia-Pacific Oscillation (APO) pattern and was defined as the paleo-APO. Its index presented an increasing trend, which implies the enhancement of a zonal thermal contrast between Asia and the North Pacific. Associated with the strengthening of the paleo-APO was the westward shift in North Pacific high pressure. Accordingly, there was less/more summer precipitation over both the middle reach of the Yangtze River and Southwest China/over North China. The high-resolution stalagmite δ18O records further support this decrease in the model precipitation. Along with the strengthening of paleo-APO from the early Holocene to the present, the eddy SLP anomalies exhibited a decreasing/increasing trend over the Eurasian landmass/the North Pacific, with a phase change of approximately 4.5 ka BP, and they both moved westward. Meanwhile, a less rainfall belt over eastern China exhibited northward propagation from southern China.
Highlights
The paleo-APO index exhibits an upward trend during the Holocene, which indicates an increase in the zonal thermal contrast between the North Pacific and Eurasia
Such a trend is possibly due to a decrease in the PU′ over the Eurasian landmass and an increase in the PU′ over the North Pacific, and there is a larger varying range over Eurasia than over the North Pacific. This result suggests that the response of atmospheric circulation over the Eurasian landmass to orbital forcing is larger than that over the North Pacific, possibly playing a more important role in modulating the zonal thermal contrast between Eurasia and the North Pacific
During the early Holocene, the paleo-APO pattern presents a negative phase with positive SLP anomalies over the Eurasian landmass and negative SLP anomalies over the North Pacific
Summary
The paleo-APO index exhibits an upward trend during the Holocene, which indicates an increase in the zonal thermal contrast between the North Pacific and Eurasia. This result suggests that the response of atmospheric circulation over the Eurasian landmass to orbital forcing is larger than that over the North Pacific, possibly playing a more important role in modulating the zonal thermal contrast between Eurasia and the North Pacific. There is more precipitation over northern China and less rainfall over the middle and lower reaches of the Yangtze River during the summer.
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