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Transient simulations for the last 300,000 years are conducted to identify how orbital insolation, greenhouse gases, and ice sheets affect variations of the East Asia winter monsoon (EAWM). Results show that the southern EAWM's dominant period is 23 kyr in response to variations in boreal winter insolation (primarily from precession), while the northern EAWM's dominant period is 100 kyr and is most strongly modulated by Northern Hemisphere ice sheets, displaying a significant latitude dependence in orbital-scale EAWM variations. The precession-modulated boreal winter insolation can control the southern EAWM by influencing zonal land-sea thermal contrast at low latitudes, while Northern Hemisphere ice sheets during glacial periods can strengthen the northern EAWM by forcing a powerful cyclonic circulation anomaly over northern Pacific. The different responses of southern and northern EAWM to orbital insolation and ice-sheet forcings can further lead to in phase or out phase variations between the southern and northern EAWM.

Plain Language Summary The East Asia winter monsoon (EAWM) has been thought to be stronger during glacial periods and weaker during interglacial periods at orbital timescales; this view highlights the impact of ice sheets at high latitudes on the EAWM but ignores the effects of variable insolation at low latitudes induced by orbital variations. Using long-term climate simulations spanning the last 300,000 years, here we show that variations of the EAWM at orbital scales arise from both and, due to the large meridional extent of the EAWM, exhibit periodicity that varies with latitude. The southern EAWM is mainly controlled by precession-modulated orbital insolation, while the northern EAWM is mainly controlled by Northern Hemisphere ice sheets. Because these two forcings operate on distinct timescales, the joint configurations of orbital insolation and ice-sheet forcings result to in phase or out phase variations between the southern and northern EAWM.