Combined Impacts of the Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation on Summer Precipitation in Eastern China During the Medieval Climate Anomaly and Little Ice Age

We investigate the joint effects of the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) on eastern China summer precipitation (ECSP) during two typical periods in the last millennium [i.e., the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA)] using simulations from five selected climate models. The multimodel mean indicates that the ECSP anomalies under the four combined AMO and PDO phases differ between the MCA and the LIA. During the MCA, the meridional wave train induced by the PDO-related convective heating over the northwestern Pacific is dominant and the zonal wave train related to the AMO is secondary. Independent of the AMO phase, deficient precipitation appears over South China in both PDO+ phases and vice versa. Meanwhile, most areas north of the Yangtze River valley feature positive anomalies in the PDO+/AMO+ phase but deficits in the PDO+/AMO- phase. In comparison, the Huanghe-Huaihe River valley and southern Northeast China receive excessive and deficient precipitation in the PDO-/AMO+ and PDO-/AMO- phases, respectively. During the LIA, the zonal wave train induced by the AMO locates more southeastward than that during the MCA and has an overwhelming impact on the ECSP. Specifically, regardless of the PDO phase, excessive ECSP exists over Northeast China and South China in both AMO+ phases and vice versa. Moreover, precipitation between the two regions is excessive when the PDO is in phase with the AMO but deficient when they are out of phase.