A Transient Modeling Study of the Latitude Dependence of East Asian Winter Monsoon Variations on Orbital Timescales

Abstract

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.