Modulation of the Arctic Oscillation and the East Asian winter climate relationships by the 11-year solar cycle

The modulation of the relationship between the Arctic Oscillation (AO) andthe East Asian winter climate by the 11-year solar cycle was investigated.During winters with high solar activity (HS), robust warming appeared innorthern Asia in a positive AO phase. This result corresponded to anenhanced anticyclonic flow at 850 hPa over northeastern Asia and a weakenedEast Asian trough (EAT) at 500 hPa. However, during winters with low solaractivity (LS), both the surface warming and the intensities of theanticyclonic flow and the EAT were much less in the presence of a positiveAO phase. The possible atmospheric processes for this 11-year solar-cyclemodulation may be attributed to the indirect influence that solar activityinduces in the structural changes of AO. During HS winters, the sea levelpressure oscillation associated with the AO became stronger, with thesignificant influence of AO extending to East Asia. In the meantime, theAO-related zonal-mean zonal winds tended to extend more into thestratosphere during HS winters, which implies a stronger coupling to the stratosphere. Thesetrends may have led to an enhanced AO phase difference; thus the associatedEast Asian climate anomalies became larger and more significant. The situation tended toreverse during LS winters. Further analyses revealed that the relationship between the winterAO and surface-climate anomalies in the following spring is also modulated by the 11-year solarcycle, with significant signals appearing only during HS phases. Solar-cycle variation shouldbe taken into consideration when the AO is used to predict winter and spring climate anomaliesover East Asia.