Abstract
Abstract
Ural blocking (UB) generally induces wintertime cooling over the Yangtze River basin (YRB), but the precipitation response varies among events. This study investigates the circulation processes underlying wet and dry YRB responses to UB events during 1979–2020. Although wet and dry UB events have comparable peak intensity, they differ markedly in extratropical evolution and tropical–subtropical circulation backgrounds. Wet UB events feature coherent downstream Rossby wave propagation, a quasi-stationary negative geopotential height anomaly over eastern Central Asia and western China, and an anticyclonic anomaly over the western North Pacific (WNP). This circulation configuration is accompanied by enhanced southwesterly moisture transport and meridional moisture convergence over the YRB, consistent with the enhanced precipitation after the UB peak. In contrast, dry UB events are preceded by a zonally extensive positive geopotential height anomaly spanning Eurasia and the North Pacific, which favors early cold-air intrusion into the YRB. Subsequent wave activity follows both midlatitude and subtropical pathways, accompanied by a deepened East Asian trough and a WNP cyclonic anomaly. These conditions weaken low-latitude moisture transport and convergence, consistent with the suppressed precipitation. The wet–dry contrast is also associated with tropical backgrounds. Suppressed Maritime Continent convection is evident before the precipitation response in wet UB events. Dry UB events preferentially occur during La Niña winters and are associated with enhanced Maritime Continent convection, and an MJO-related signal on the intraseasonal time scale. These results indicate that UB-related YRB precipitation depends on the joint configuration of extratropical evolution and tropical–subtropical circulation backgrounds.