Extended-Range Precursors for Summer Consecutive Extreme Rainfall in the Yangtze River Valley Related to Intraseasonal Variations of the Pacific-Japan Teleconnection

In summer, the Yangtze River valley (YRV) in central-eastern China frequently suffers consecutive extreme rainfall (CER) events, causing floods and huge damages. On the daily timescale, our previous study has shown that the Pacific-Japan (PJ) teleconnection is related to the CER events over the YRV, and is a source for long-term (lead time of about 10 days) forecasts of CER events. To facilitate extended-range (lead time of about 20 days) prediction of CER, in the present study, we use the band-pass filter for the PJ teleconnection to keep only the prolonged atmospheric circulation information at the intraseasonal timescale and try to identify more advanced precursors for the CER events over the YRV. Power spectrum analysis was implemented on 9-day sliding mean of the precipitation anomalies. It is found that summer precipitation in YRV has significant 10-40-day oscillations, and the CER events over the YRV are affected by the intraseasonal oscillation (ISO) of the PJ teleconnection. When the ISO of the PJ teleconnection enters its positive phase, it is favorable for CER events to occur. Dynamic diagnoses and model experiments demonstrate that the ISO of the PJ teleconnection is attributed to the intraseasonal convective activities and diabatic heating around the Philippines, which generate significant northward energy dispersion and propagation of Rossby waves up to 16 days prior to occurrences of the CER events in the YRV. The ISO of the PJ teleconnection and the convective activities in the tropical South Asia provide significant and earlier precursors for extended-range forecasts of the CER events along the YRV.