This study compares the tropical and extratropical circulation anomalies that affect the extreme rainfall over the Yangtze River basin (YRB) in summer. In the lower troposphere, the tropical circulation anomalies manifest as an anticyclonic anomaly over the tropical western North Pacific (WNP) and the extratropical circulation anomalies are characterized by northeasterly anomalies to the north of the YRB. It is found that the tropical and extratropical circulation anomalies tend to be independent of each other. Compared to the tropical ones, the extratropical circulation anomalies can more efficiently induce extreme rainfall, as the associated rainfall anomalies are more intensified. By contrast, the tropical ones favor more the persistence of enhanced rainfall. This is because the tropical WNP anticyclonic anomaly exhibits notable quasi-biweekly feature and provides a favorable background for the enhanced YRB rainfall. By contrast, the northeasterly anomalies are dominated by synoptic variability, in association with a mid-latitude and a high-latitude wave train. The concurrent occurrence of the tropical and extratropical circulation anomalies is more prone to extreme and persistent rainfall.

atmospheric circulation,Extreme rainfall,anomalies