Abstract/Summary

This paper reports a consistent seesaw relationship between interdecadal precipitation variability over North China and the Southwest United States (US), which can be found in observations and simulations with several models. Idealized model simulations suggest the seesaw could be mainly driven by the Interdecadal Pacific Oscillation (IPO), through a large-scale circulation anomaly occupying the entire northern North Pacific, while the Atlantic Multidecadal Oscillation (AMO) contributes oppositely and less. Modulation of precipitation by the IPO tends to be intensified when the AMO is in the same phase. The warm IPO phase is associated with an anomalous cyclone over the northern North Pacific and consequently, anomalous southwesterly winds bring more moisture and rainfall to the southwest US, while northwesterly wind anomalies prevail over North China with negative rainfall anomalies. The east-west seesaw of rainfall anomalies reverses sign when the circulation anomaly becomes anticyclonic during the cold IPO phase. The IPO-related tropical SST anomalies affect the meridional temperature gradient over the North Pacific and adjacent regions and the mean meridional circulation. In the northern North Pacific, the atmospheric response to IPO forcing imposes an equivalent barotropic structure throughout the troposphere. An important impliciation from this study is the potential predictability of drought-related water stresses over these arid and semiarid regions, with the progress of our understanding and prediction of the IPO and AMO.