Impact of the August Asian–Pacific Oscillation on Autumn Precipitation in Central Eastern China

The August Asian–Pacific Oscillation (APO) plays an important role in the variability of autumn (September ~ October mean) precipitation in central eastern China (CEC). Using observational and reanalysis data, the impact of the August APO on autumn CEC precipitation from 1960 to 2016 was studied. The statistical result showed that August APO is closely linked to the autumn precipitation anomalies in CEC with a significant positive correlation (r = 0.45). Further analysis revealed that when the APO is strong, the strengthened East Asian trough and the North Pacific high / vertical shear occur in the mid-lower / upper troposphere, resulting in anomalous southerly along the East Asia coast, which are favorable for strengthening the anomalous convergence and upward movement of moist warm air from the northwestern Pacific and arid cold air from the north China, introducing more precipitation, but that this configuration became much diminished during weak APO years. The possible mechanism can be explained as the thermal effect in the mid-upper troposphere can last from August until autumn, and the corresponding concurrent thermal effect would lead to anomalies in both atmospheric circulation and precipitation. Additionally, though an evidently negative relationship between preceding Niño indices and autumn CEC precipitation was revealed, the August APO induced changes in autumn CEC precipitation is greater than those of Niño indices, whether interannual or interdecadal changes, further indicating that the APO is an effective signal for precipitation prediction in CEC.