The intensifying relationship between heatwaves in the mid-lower reaches of the Yangtze River valley and the upstream atmospheric wave train after the 2000s

The frequency and duration of heatwaves are rapidly increasing worldwide under the background of global warming. This trend is also observed in the mid-lower reaches of the Yangtze River valley (MLYRV), raising great public concern due to its significant impacts. This study identifies a wave train involving the positive phase of the North Atlantic Oscillation (NAO), the Ural blocking (UB), and an anticyclone over the MLYRV, which is closely linked to MLYRV heatwaves during 1970-2023. Our findings indicate that the development of the anticyclone over the MLYRV is associated with the energy dispersion of the UB under the regulation of the North Atlantic jet (NAJ). Further analyses reveal that the correlation of heatwave frequency with the NAO index and UB days is significantly stronger during 2001-2023 (P2) compared to 1970-2000 (P1). This strengthening may be attributable to the northeastward extension of the NAJ to northern Eurasia during P2, modulated by the positive phase of the Atlantic Multidecadal Oscillation (AMO). Such strong zonal winds over high latitudes of Eurasia are expected to favor low-latitude UB, and its robust downstream energy dispersion enhances the development of heatwaves during P2. In contrast, the weaker zonal winds over high latitudes of Eurasia during P1 favor highlatitude UB under the regulation of the negative phase of the AMO, and the correlation between the UB and heatwaves is less significant due to weak energy dispersion from the high-latitude UB to the MLYRV. Consequently, the UB acts as a crucial bridge within this wave train, facilitating the energy transfer necessary for heatwave formation.